Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
Fixes: 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified") Cc: stable@vger.kernel.org Signed-off-by: Baoquan He bhe@redhat.com Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Vlastimil Babka vbabka@suse.cz --- mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA + bool managed_dma; +#endif
/* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP;
#ifdef CONFIG_ZONE_DMA + managed_dma = has_managed_dma(); + for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) { + if (!managed_dma) { + kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i]; + continue; + } kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];continue;}
This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Thanks, Hyeonggon.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On 12/13/21 at 01:43pm, Hyeonggon Yoo wrote:
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
The problem is this is a generic issue on x86_64, and will be warned out always on all x86_64 systems, but not on a certain machine or a certain type of machine. If not fixed, we can always see it in kdump kernel. The way things are, it doesn't casue system or device collapse even if dma-kmalloc can't provide buffer or provide buffer from zone NORMAL.
I have got bug reports several times from different people, and we have several bugs tracking this inside Redhat. I think nobody want to see this appearing in customers' monitor w or w/o a note. If we have to leave it with that, it's a little embrassing.
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];continue;}This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
This is a great question. Honestly, no,
On the surface, it's obviously not what we want, We should never give user a zone NORMAL memory when they ask for zone DMA memory. If going to this specific x86_64 ARCH where this problem is observed, I prefer to give it zone DMA32 memory if zone DMA allocation failed. Because we rarely have ISA device deployed which requires low 16M DMA buffer. The zone DMA is just in case. Thus, for kdump kernel, we have been trying to make sure zone DMA32 has enough memory to satisfy PCIe device DMA buffer allocation, I don't remember we made any effort to do that for zone DMA.
Now the thing is that the nothing serious happened even if sr_probe() doesn't get DMA buffer from zone DMA. And it works well when I feed it with zone NORMAL memory instead with this patch applied.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On 12/14/21 06:32, Baoquan He wrote:
On 12/13/21 at 01:43pm, Hyeonggon Yoo wrote:
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
Could have included the warning headline too.
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
The problem is this is a generic issue on x86_64, and will be warned out always on all x86_64 systems, but not on a certain machine or a certain type of machine. If not fixed, we can always see it in kdump kernel. The way things are, it doesn't casue system or device collapse even if dma-kmalloc can't provide buffer or provide buffer from zone NORMAL.
I have got bug reports several times from different people, and we have several bugs tracking this inside Redhat. I think nobody want to see this appearing in customers' monitor w or w/o a note. If we have to leave it with that, it's a little embrassing.
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];
The right side could be just 's'?
continue;}This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
This is a great question. Honestly, no,
On the surface, it's obviously not what we want, We should never give user a zone NORMAL memory when they ask for zone DMA memory. If going to this specific x86_64 ARCH where this problem is observed, I prefer to give it zone DMA32 memory if zone DMA allocation failed. Because we rarely have ISA device deployed which requires low 16M DMA buffer. The zone DMA is just in case. Thus, for kdump kernel, we have been trying to make sure zone DMA32 has enough memory to satisfy PCIe device DMA buffer allocation, I don't remember we made any effort to do that for zone DMA.
Now the thing is that the nothing serious happened even if sr_probe() doesn't get DMA buffer from zone DMA. And it works well when I feed it with zone NORMAL memory instead with this patch applied.
If doesn't feel right to me to fix (or rather workaround) this on the level of kmalloc caches just because the current reports come from there. If we decide it's acceptable for kdump kernel to return !ZONE_DMA memory for GFP_DMA requests, then it should apply at the page allocator level for all allocations, not just kmalloc().
Also you mention above you'd prefer ZONE_DMA32 memory, while chances are this approach of using KMALLOC_NORMAL caches will end up giving you ZONE_NORMAL. On the page allocator level it would be much easier to implement a fallback from non-populated ZONE_DMA to ZONE_DMA32 specifically.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On Tue, 14 Dec 2021, Vlastimil Babka wrote:
If doesn't feel right to me to fix (or rather workaround) this on the level of kmalloc caches just because the current reports come from there. If we decide it's acceptable for kdump kernel to return !ZONE_DMA memory for GFP_DMA requests, then it should apply at the page allocator level for all allocations, not just kmalloc().
Also you mention above you'd prefer ZONE_DMA32 memory, while chances are this approach of using KMALLOC_NORMAL caches will end up giving you ZONE_NORMAL. On the page allocator level it would be much easier to implement a fallback from non-populated ZONE_DMA to ZONE_DMA32 specifically.
Well this only works if the restrictions on the physical memory addresses of each platform make that possible.
On Tue, Dec 14, 2021 at 11:09:23AM +0100, Vlastimil Babka wrote:
On 12/14/21 06:32, Baoquan He wrote:
On 12/13/21 at 01:43pm, Hyeonggon Yoo wrote:
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
Could have included the warning headline too.
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
The problem is this is a generic issue on x86_64, and will be warned out always on all x86_64 systems, but not on a certain machine or a certain type of machine. If not fixed, we can always see it in kdump kernel. The way things are, it doesn't casue system or device collapse even if dma-kmalloc can't provide buffer or provide buffer from zone NORMAL.
I have got bug reports several times from different people, and we have several bugs tracking this inside Redhat. I think nobody want to see this appearing in customers' monitor w or w/o a note. If we have to leave it with that, it's a little embrassing.
Okay Then, Do you care if it just fails (without warning) or is allocated from ZONE_DMA32?
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];The right side could be just 's'?
continue;}This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
This is a great question. Honestly, no,
On the surface, it's obviously not what we want, We should never give user a zone NORMAL memory when they ask for zone DMA memory. If going to this specific x86_64 ARCH where this problem is observed, I prefer to give it zone DMA32 memory if zone DMA allocation failed. Because we rarely have ISA device deployed which requires low 16M DMA buffer. The zone DMA is just in case. Thus, for kdump kernel, we have been trying to make sure zone DMA32 has enough memory to satisfy PCIe device DMA buffer allocation, I don't remember we made any effort to do that for zone DMA.
Now the thing is that the nothing serious happened even if sr_probe() doesn't get DMA buffer from zone DMA. And it works well when I feed it with zone NORMAL memory instead with this patch applied.
If doesn't feel right to me to fix (or rather workaround) this on the level of kmalloc caches just because the current reports come from there. If we decide it's acceptable for kdump kernel to return !ZONE_DMA memory for GFP_DMA requests, then it should apply at the page allocator level for all allocations, not just kmalloc().
I think that will make it much easier to manage the code.
Also you mention above you'd prefer ZONE_DMA32 memory, while chances are this approach of using KMALLOC_NORMAL caches will end up giving you ZONE_NORMAL. On the page allocator level it would be much easier to implement a fallback from non-populated ZONE_DMA to ZONE_DMA32 specifically.
Hello Baoquan and Vlastimil.
I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve this problem. Devices that requires ZONE_DMA is rare but we still support them.
If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels, the problem will be hard to find.
What about one of those?:
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages.
2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc()
3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32 and see what happens
Thanks, Hyeonggon.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On Wed, Dec 15, 2021 at 04:48:26AM +0000, Hyeonggon Yoo wrote:
Hello Baoquan and Vlastimil.
I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve this problem. Devices that requires ZONE_DMA is rare but we still support them.
If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels, the problem will be hard to find.
Sorry, I sometimes forget validating my english writing :(
What I meant:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
Devices that requires ZONE_DMA memory is rare but we still support them.
If we use ZONE_DMA32 memory instead of ZONE_DMA in kdump kernels, It will be hard to the problem when we use devices that can use only ZONE_DMA memory.
What about one of those?:
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32
(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThanks, Hyeonggon.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happens
This is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1, a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
On 12/15/21 08:27, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
My understanding is that kdump kernel can only use physical memory that it got reserved by the main kernel, and the main kernel will reserve some block of memory that doesn't include any pages from ZONE_DMA (first 16MB of physical memory or whatnot). By looking at the "crashkernel" parameter documentation in kernel-parameters.txt it seems we only care about below-4GB/above-4GB split. So it can easily happen that ZONE_DMA in the kdump kernel will be completely empty because the main kernel was using all of it.
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThis is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1, a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory
But if ZONE_DMA is not populated, where will it get the bounce buffer from? I guess nowhere and the problem still exists?
that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
From: Vlastimil Babka
Sent: 15 December 2021 10:34
On 12/15/21 08:27, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
My understanding is that kdump kernel can only use physical memory that it got reserved by the main kernel, and the main kernel will reserve some block of memory that doesn't include any pages from ZONE_DMA (first 16MB of physical memory or whatnot).
...
Is there still any support for any of the very old hardware that could only support 24bit DMA?
I think the AMD PCnet-ISA and PCnet-PCI ethernet (lance) were both 32bit masters. (I don't remember ever having to worry about physical addresses.) I'm sure I remember some old SCSI boards only being able to do 24bit DMA. But I can't remember which bus interface they were. Unlikely to be ISA because it has always been hard to get a motherboard DMA channel into 'cascade mode'.
Might have been some EISA boards - anyone still use those? So we are left with early PCI boards.
It really is worth looking at what actually needs it at all.
David
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On 12/15/21 at 11:34am, Vlastimil Babka wrote:
On 12/15/21 08:27, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
My understanding is that kdump kernel can only use physical memory that it got reserved by the main kernel, and the main kernel will reserve some block of memory that doesn't include any pages from ZONE_DMA (first 16MB of physical memory or whatnot). By looking at the "crashkernel" parameter documentation in kernel-parameters.txt it seems we only care about below-4GB/above-4GB split. So it can easily happen that ZONE_DMA in the kdump kernel will be completely empty because the main kernel was using all of it.
Exactly as you said. Even before below regression commit added, we only have 0~640K reused in kdump kernel. We resued the 1st 640K not because we need it for zone DMA, just the 1st 640K is needed by BIOS/firmwre during early stage of system bootup. So there are tens of or several hundred KB left for managed pages in zone DMA except of those firmware reserved area in the 1st 640K. After below commit, the 1st 1M is reserved with memblock_reserve(), so no any physicall memory added to zone DMA. Then we see the allocation failure.
When we prepare environment for kdump kernel, usually we will customize a initramfs to includes those necessary ko. E.g a storage device is dump target, its driver must be loaded. If a network dump specified, network driver is needed. I never see a ISA device or a device of 24bit addressing limit is needed in kdump kernel.
6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified")
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThis is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1, a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory
But if ZONE_DMA is not populated, where will it get the bounce buffer from? I guess nowhere and the problem still exists?
Agree. When I investigated other ARCHs, arm64 has a fascinating setup for zone DMA/DMA32. It defaults to have all low 4G memory into zone DMA, but empty zone DMA32. Only if ACPI/DT reports <32 bit addressing devices, it will set it as limit of zone DMA.
ZONE_DMA ZONE_DMA32 arm64 0~X X~4G (X is got from ACPI or DT. Otherwise it's 4G by default, DMA32 is empty)
that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
On Wed, Dec 15, 2021 at 08:27:10AM +0100, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThis is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1,
Hmm I think step 1) will be needed if someone is allocating pages from DMA zone not using kmalloc or DMA API. (for example directly allocating from buddy allocator) is there such cases?
a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
That's good. this cleanup will also remove unnecessary limitations.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
On 12/17/21 at 11:38am, Hyeonggon Yoo wrote:
On Wed, Dec 15, 2021 at 08:27:10AM +0100, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThis is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1,
Hmm I think step 1) will be needed if someone is allocating pages from DMA zone not using kmalloc or DMA API. (for example directly allocating from buddy allocator) is there such cases?
I think Christoph meant to take off the warning. I will post a patch to mute the warning if it's requesting page from DMA zone which has no managed pages.
a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
That's good. this cleanup will also remove unnecessary limitations.
I searched and investigated several callsites where kmalloc(GFP_DMA) is called. E.g drivers/scsi/sr.c: sr_probe(). The scsi sr driver doesn't check DMA supporting capibility at all, e.g the dma limit, to set the dma mask or coherent_dma_mask. If we want to convert the kmalloc(GFP_DMA) to dma_alloc* API, scsi sr drvier developer/expert's suggestion and help is necessary. Either someone who knows this well help to change it, or give suggestion how to change so that I can do it.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
On Wed, Dec 15, 2021 at 08:27:10AM +0100, Christoph Hellwig wrote:
On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
What is the problem with zones in kdump kernels?
Devices that requires ZONE_DMA memory is rare but we still support them.
Indeed.
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages. 2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc() 3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
and see what happensThis is the right thing to do, but it will take a while. In fact I dont think we really need the warning in step 1, a simple grep already allows to go over them. I just looked at the uses of GFP_DMA in drivers/scsi for example, and all but one look bogus.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
The way this works is that the dma_map* calls will bounce buffer memory that does to fall into the addressing limitations. This is a performance overhead, but allows drivers to address all memory in a system. If the driver controls memory allocation it should use one of the dma_alloc_* APIs that allocate addressable memory from the start. The allocator will dip into ZONE_DMA and ZONE_DMA32 when needed.
Hello Christoph, Baoquan and I started this cleanup. But we're a bit confused. I want to ask you something.
- Did you mean dma_map_* can handle arbitrary buffer, (and dma_map_* will bounce buffer when necessary) Can we assume it on every architectures and buses?
Reading at the DMA API documentation and code (dma_map_page_attrs(), dma_direct_map_page()), I'm not sure about that.
In the documentation: (dma_map_single) Further, the DMA address of the memory must be within the dma_mask of the device (the dma_mask is a bit mask of the addressable region for the device, i.e., if the DMA address of the memory ANDed with the dma_mask is still equal to the DMA address, then the device can perform DMA to the memory). To ensure that the memory allocated by kmalloc is within the dma_mask, the driver may specify various platform-dependent flags to restrict the DMA address range of the allocation (e.g., on x86, GFP_DMA guarantees to be within the first 16MB of available DMA addresses, as required by ISA devices).
- In what function does the DMA API do bounce buffering?
Thanks a lot, Hyeonggon
On 12/15/21 at 07:03am, Hyeonggon Yoo wrote:
On Wed, Dec 15, 2021 at 04:48:26AM +0000, Hyeonggon Yoo wrote:
Hello Baoquan and Vlastimil.
I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve this problem. Devices that requires ZONE_DMA is rare but we still support them.
If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels, the problem will be hard to find.
Sorry, I sometimes forget validating my english writing :(
What I meant:
I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem.
Yeah, if it's really <32bit addressing limit on device, it doesn't solve problem. Not sure if devices really has the limitation when kmalloc(GFP_DMA) is invoked kernel driver.
Devices that requires ZONE_DMA memory is rare but we still support them.
If we use ZONE_DMA32 memory instead of ZONE_DMA in kdump kernels, It will be hard to the problem when we use devices that can use only ZONE_DMA memory.
What about one of those?:
1) Do not call warn_alloc in page allocator if will always fail to allocate ZONE_DMA pages.
Seems we can do like below.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7c7a0b5de2ff..843bc8e5550a 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4204,7 +4204,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...) va_list args; static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1);
- if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs)) + if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) || + (gfp_mask & __GFP_DMA) && !has_managed_dma()) return;
2) let's check all callers of kmalloc with GFP_DMA if they really need GFP_DMA flag and replace those by DMA API or just remove GFP_DMA from kmalloc()
I grepped and got a list, I will try to start with several easy place, see if we can do something to improve. start with.
3) Drop support for allocating DMA memory from slab allocator (as Christoph Hellwig said) and convert them to use DMA32(as Christoph Hellwig said) and convert them to use *DMA API*
Yes, that will be ideal result. This is equivalent to 2), or depends on 2).
and see what happensThanks, Hyeonggon.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On 12/14/21 at 11:09am, Vlastimil Babka wrote:
On 12/14/21 06:32, Baoquan He wrote:
On 12/13/21 at 01:43pm, Hyeonggon Yoo wrote:
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
Could have included the warning headline too.
Sure, I will paste the whole warning when repost.
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
The problem is this is a generic issue on x86_64, and will be warned out always on all x86_64 systems, but not on a certain machine or a certain type of machine. If not fixed, we can always see it in kdump kernel. The way things are, it doesn't casue system or device collapse even if dma-kmalloc can't provide buffer or provide buffer from zone NORMAL.
I have got bug reports several times from different people, and we have several bugs tracking this inside Redhat. I think nobody want to see this appearing in customers' monitor w or w/o a note. If we have to leave it with that, it's a little embrassing.
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];The right side could be just 's'?
Right, will see if we will take another way, will change it if keeping this way.
continue;}This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
This is a great question. Honestly, no,
On the surface, it's obviously not what we want, We should never give user a zone NORMAL memory when they ask for zone DMA memory. If going to this specific x86_64 ARCH where this problem is observed, I prefer to give it zone DMA32 memory if zone DMA allocation failed. Because we rarely have ISA device deployed which requires low 16M DMA buffer. The zone DMA is just in case. Thus, for kdump kernel, we have been trying to make sure zone DMA32 has enough memory to satisfy PCIe device DMA buffer allocation, I don't remember we made any effort to do that for zone DMA.
Now the thing is that the nothing serious happened even if sr_probe() doesn't get DMA buffer from zone DMA. And it works well when I feed it with zone NORMAL memory instead with this patch applied.
If doesn't feel right to me to fix (or rather workaround) this on the level of kmalloc caches just because the current reports come from there. If we decide it's acceptable for kdump kernel to return !ZONE_DMA memory for GFP_DMA requests, then it should apply at the page allocator level for all allocations, not just kmalloc().
Also you mention above you'd prefer ZONE_DMA32 memory, while chances are this approach of using KMALLOC_NORMAL caches will end up giving you ZONE_NORMAL. On the page allocator level it would be much easier to implement a fallback from non-populated ZONE_DMA to ZONE_DMA32 specifically.
This could be do-able. I count this in when investigate all suggested solutions. Thanks.
On Tue, Dec 14, 2021 at 01:32:53PM +0800, Baoquan He wrote:
On 12/13/21 at 01:43pm, Hyeonggon Yoo wrote:
Hello Baoquan. I have a question on your code.
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
What is problem here?
The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page.
Looking at warn, I don't understand what the problem is.
The problem is this is a generic issue on x86_64, and will be warned out always on all x86_64 systems, but not on a certain machine or a certain type of machine. If not fixed, we can always see it in kdump kernel. The way things are, it doesn't casue system or device collapse even if dma-kmalloc can't provide buffer or provide buffer from zone NORMAL.
I have got bug reports several times from different people, and we have several bugs tracking this inside Redhat. I think nobody want to see this appearing in customers' monitor w or w/o a note. If we have to leave it with that, it's a little embrassing.
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];continue;}This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want?
This is a great question. Honestly, no,
On the surface, it's obviously not what we want, We should never give user a zone NORMAL memory when they ask for zone DMA memory. If going to this specific x86_64 ARCH where this problem is observed, I prefer to give it zone DMA32 memory if zone DMA allocation failed. Because we rarely have ISA device deployed which requires low 16M DMA buffer. The zone DMA is just in case. Thus, for kdump kernel, we have been trying to make sure zone DMA32 has enough memory to satisfy PCIe device DMA buffer allocation, I don't remember we made any effort to do that for zone DMA.
Now the thing is that the nothing serious happened even if sr_probe() doesn't get DMA buffer from zone DMA. And it works well when I feed it with zone NORMAL memory instead with this patch applied.
Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that.
Yeah, I have the same guess too for get_capabilities(), not sure about other callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is the right way to call people when the first name is the same. Correct me if it's wrong), any buffer requested from kmalloc can be used by device driver. Means device enforces getting memory inside addressing limit for those DMA transferring buffer which is usually large, Megabytes level with vmalloc() or alloc_pages(), but doesn't care about this kind of small piece buffer memory allocated with kmalloc()? Just a guess, please tell a counter example if anyone happens to know, it could be easy.
My understanding is any buffer requested from kmalloc (without GFP_DMA/DMA32) can be used by device driver because it allocates continuous physical memory. It doesn't mean that buffer allocated with kmalloc is free of addressing limitation.
the addressing limitation comes from the capability of device, not allocation size. if you allocate memory using alloc_pages() or kmalloc(), the device has same limitation. and vmalloc can't be used for devices because they have no MMU.
But we can map memory outside DMA zone into bounce buffer (which resides in DMA zone) using DMA API.
Thanks, Hyeonggon.
kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,-- 2.17.2
On Fri, Dec 17, 2021 at 11:38:27AM +0000, Hyeonggon Yoo wrote:
My understanding is any buffer requested from kmalloc (without GFP_DMA/DMA32) can be used by device driver because it allocates continuous physical memory. It doesn't mean that buffer allocated with kmalloc is free of addressing limitation.
Yes.
the addressing limitation comes from the capability of device, not allocation size. if you allocate memory using alloc_pages() or kmalloc(), the device has same limitation. and vmalloc can't be used for devices because they have no MMU.
vmalloc can be used as well, it just needs to be setup as a scatterlist and needs a little lover for DMA challenged platforms with the invalidate_kernel_vmap_range and flush_kernel_vmap_range helpers.
But we can map memory outside DMA zone into bounce buffer (which resides in DMA zone) using DMA API.
Yes, although in a few specific cases the bounce buffer could also come from somewhere else.
Hello Christoph.
On Tue, Dec 21, 2021 at 09:56:23AM +0100, Christoph Hellwig wrote:
On Fri, Dec 17, 2021 at 11:38:27AM +0000, Hyeonggon Yoo wrote:
My understanding is any buffer requested from kmalloc (without GFP_DMA/DMA32) can be used by device driver because it allocates continuous physical memory. It doesn't mean that buffer allocated with kmalloc is free of addressing limitation.
Yes.
the addressing limitation comes from the capability of device, not allocation size. if you allocate memory using alloc_pages() or kmalloc(), the device has same limitation. and vmalloc can't be used for devices because they have no MMU.
vmalloc can be used as well, it just needs to be setup as a scatterlist and needs a little lover for DMA challenged platforms with the invalidate_kernel_vmap_range and flush_kernel_vmap_range helpers.
Oh I misunderstood this. Underlying physical address of vmalloc()-allocated memory can be mapped using DMA API, and it needs to be setup as scatterlist because the allocated memory is not physically continuous. Right?
BTW, looking at the API I think the scsi case can be converted to use dma_alloc_pages(). but driver requires 512 bytes of buffer and the API supports allocating by at least page size.
It's not a big problem as it allocates a single buffer but in other cases maybe not. Can't we use dma pool for non-coherent pages?
Thanks, Hyeonggon.
But we can map memory outside DMA zone into bounce buffer (which resides in DMA zone) using DMA API.
Yes, although in a few specific cases the bounce buffer could also come from somewhere else.
On Wed, Dec 22, 2021 at 12:37:03PM +0000, Hyeonggon Yoo wrote:
Oh I misunderstood this. Underlying physical address of vmalloc()-allocated memory can be mapped using DMA API, and it needs to be setup as scatterlist because the allocated memory is not physically continuous. Right?
Yes.
BTW, looking at the API I think the scsi case can be converted to use dma_alloc_pages(). but driver requires 512 bytes of buffer and the API supports allocating by at least page size.
Overallocating is not generally a problem, but if the allocations are for a slow path it might make more sense to stick to dma_map_* and bounce buffer if needed.
It's not a big problem as it allocates a single buffer but in other cases maybe not. Can't we use dma pool for non-coherent pages?
No.
On 12/13/21 6:27 AM, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 Workqueue: events_unbound async_run_entry_fn Call Trace: dump_stack_lvl+0x57/0x72 warn_alloc.cold+0x72/0xd6 __alloc_pages_slowpath.constprop.0+0xf56/0xf70 __alloc_pages+0x23b/0x2b0 allocate_slab+0x406/0x630 ___slab_alloc+0x4b1/0x7e0 ? sr_probe+0x200/0x600 ? lock_acquire+0xc4/0x2e0 ? fs_reclaim_acquire+0x4d/0xe0 ? lock_is_held_type+0xa7/0x120 ? sr_probe+0x200/0x600 ? __slab_alloc+0x67/0x90 __slab_alloc+0x67/0x90 ? sr_probe+0x200/0x600 ? sr_probe+0x200/0x600 kmem_cache_alloc_trace+0x259/0x270 sr_probe+0x200/0x600 ...... bus_probe_device+0x9f/0xb0 device_add+0x3d2/0x970 ...... __scsi_add_device+0xea/0x100 ata_scsi_scan_host+0x97/0x1d0 async_run_entry_fn+0x30/0x130 process_one_work+0x2b0/0x5c0 worker_thread+0x55/0x3c0 ? process_one_work+0x5c0/0x5c0 kthread+0x149/0x170 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Mem-Info: ......
The above failure happened when calling kmalloc() to allocate buffer with GFP_DMA. It requests to allocate slab page from DMA zone while no managed pages in there. sr_probe() --> get_capabilities() --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
The DMA zone should be checked if it has managed pages, then try to create dma-kmalloc.
Fixes: 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified") Cc: stable@vger.kernel.org Signed-off-by: Baoquan He bhe@redhat.com
Acked-by: John Donnelly john.p.donnelly@oracle.com Tested-by: John Donnelly john.p.donnelly@oracle.com
Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Vlastimil Babka vbabka@suse.cz
mm/slab_common.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/slab_common.c b/mm/slab_common.c index e5d080a93009..ae4ef0f8903a 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) { int i; enum kmalloc_cache_type type; +#ifdef CONFIG_ZONE_DMA
- bool managed_dma;
+#endif /* * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) slab_state = UP; #ifdef CONFIG_ZONE_DMA
- managed_dma = has_managed_dma();
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {
if (!managed_dma) {kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];continue;} kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( kmalloc_info[i].name[KMALLOC_DMA], kmalloc_info[i].size,
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
Please just switch the sr allocation to use GFP_KERNEL without GFP_DMA. The block layer will do the proper bounce buffering underneath for the very unlikely case that we're actually using the single HBA driver that has ISA DMA addressing limitations.
Same for the ch drive, btw.
On 12/14/21 10:31 AM, Christoph Hellwig wrote:
On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote:
Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. However, it will fail if DMA zone has no managed pages. The failure can be seen in kdump kernel of x86_64 as below:
Please just switch the sr allocation to use GFP_KERNEL without GFP_DMA. The block layer will do the proper bounce buffering underneath for the very unlikely case that we're actually using the single HBA driver that has ISA DMA addressing limitations.
Same for the ch drive, btw.
Hi,
Is CONFIG_ZONE_DMA even needed anymore in x86_64 ?
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