From: Mike Rapoport rppt@linux.ibm.com
Hi,
@Andrew, this is based on v5.11-mmotm-2021-02-18-18-29 with the previous version reverted
Commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") exposed several issues with the memory map initialization and these patches fix those issues.
Initially there were crashes during compaction that Qian Cai reported back in April [1]. It seemed back then that the problem was fixed, but a few weeks ago Andrea Arcangeli hit the same bug [2] and there was an additional discussion at [3].
I didn't appreciate variety of ways BIOSes can report memory in the first megabyte, so previous versions of this set caused all kinds of troubles.
The last version that implicitly extended node/zone to cover the complete section might also have unexpected side effects, so this time I'm trying to move in forward in baby steps.
This is mostly a return to the fist version that simply merges init_unavailable_pages() into memmap_init() so that the only effective change would be more sensible zone/node links in unavailable struct pages.
For now, I've dropped the patch that tried to make ZONE_DMA to span pfn 0 because it didn't cause any issues for really long time and there are way to many hidden mines around this.
I have an ugly workaround for "pfn 0" issue that IMHO is the safest way to deal with it until it could be gradually fixed properly:
https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/commit/?h=mem...
v7: * add handling of section end that span beyond the populated zones
v6: https://lore.kernel.org/lkml/20210222105728.28636-1-rppt@kernel.org * only interleave initialization of unavailable pages in memmap_init(), so that it is essentially includes init_unavailable_pages().
v5: https://lore.kernel.org/lkml/20210208110820.6269-1-rppt@kernel.org * extend node/zone spans to cover complete sections, this allows to interleave the initialization of unavailable pages with "normal" memory map init. * drop modifications to x86 early setup
v4: https://lore.kernel.org/lkml/20210130221035.4169-1-rppt@kernel.org/ * make sure pages in the range 0 - start_pfn_of_lowest_zone are initialized even if an architecture hides them from the generic mm * finally make pfn 0 on x86 to be a part of memory visible to the generic mm as reserved memory.
v3: https://lore.kernel.org/lkml/20210111194017.22696-1-rppt@kernel.org * use architectural zone constraints to set zone links for struct pages corresponding to the holes * drop implicit update of memblock.memory * add a patch that sets pfn 0 to E820_TYPE_RAM on x86
v2: https://lore.kernel.org/lkml/20201209214304.6812-1-rppt@kernel.org/): * added patch that adds all regions in memblock.reserved that do not overlap with memblock.memory to memblock.memory in the beginning of free_area_init()
[1] https://lore.kernel.org/lkml/8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw [2] https://lore.kernel.org/lkml/20201121194506.13464-1-aarcange@redhat.com [3] https://lore.kernel.org/mm-commits/20201206005401.qKuAVgOXr%akpm@linux-found...
Mike Rapoport (1): mm/page_alloc.c: refactor initialization of struct page for holes in memory layout
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
From: Mike Rapoport rppt@linux.ibm.com
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com --- mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } }
+#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/* + * Only struct pages that correspond to ranges defined by memblock.memory + * are zeroed and initialized by going through __init_single_page() during + * memmap_init_zone(). + * + * But, there could be struct pages that correspond to holes in + * memblock.memory. This can happen because of the following reasons: + * - phyiscal memory bank size is not necessarily the exact multiple of the + * arbitrary section size + * - early reserved memory may not be listed in memblock.memory + * - memory layouts defined with memmap= kernel parameter may not align + * nicely with memmap sections + * + * Explicitly initialize those struct pages so that: + * - PG_Reserved is set + * - zone and node links point to zone and node that span the page + */ +static u64 __meminit init_unavailable_range(unsigned long spfn, + unsigned long epfn, + int zone, int node) +{ + unsigned long pfn; + u64 pgcnt = 0; + + for (pfn = spfn; pfn < epfn; pfn++) { + if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) { + pfn = ALIGN_DOWN(pfn, pageblock_nr_pages) + + pageblock_nr_pages - 1; + continue; + } + __init_single_page(pfn_to_page(pfn), pfn, zone, node); + __SetPageReserved(pfn_to_page(pfn)); + pgcnt++; + } + + return pgcnt; +} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn, + int zone, int node) +{ + return 0; +} +#endif + void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone); + static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn; + u64 pgcnt = 0;
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE); + + if (hole_pfn < start_pfn) + pgcnt += init_unavailable_range(hole_pfn, start_pfn, + zone_id, nid); + hole_pfn = end_pfn; } + +#ifdef CONFIG_SPARSEMEM + end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION); + if (hole_pfn < end_pfn) + pgcnt += init_unavailable_range(hole_pfn, end_pfn, + zone_id, nid); +#endif + + if (pgcnt) + pr_info(" %s zone: %lld pages in unavailable ranges\n", + zone->name, pgcnt); }
static int zone_batchsize(struct zone *zone) @@ -7092,88 +7156,6 @@ void __init free_area_init_memoryless_node(int nid) free_area_init_node(nid); }
-#if !defined(CONFIG_FLAT_NODE_MEM_MAP) -/* - * Initialize all valid struct pages in the range [spfn, epfn) and mark them - * PageReserved(). Return the number of struct pages that were initialized. - */ -static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn) -{ - unsigned long pfn; - u64 pgcnt = 0; - - for (pfn = spfn; pfn < epfn; pfn++) { - if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) { - pfn = ALIGN_DOWN(pfn, pageblock_nr_pages) - + pageblock_nr_pages - 1; - continue; - } - /* - * Use a fake node/zone (0) for now. Some of these pages - * (in memblock.reserved but not in memblock.memory) will - * get re-initialized via reserve_bootmem_region() later. - */ - __init_single_page(pfn_to_page(pfn), pfn, 0, 0); - __SetPageReserved(pfn_to_page(pfn)); - pgcnt++; - } - - return pgcnt; -} - -/* - * Only struct pages that are backed by physical memory are zeroed and - * initialized by going through __init_single_page(). But, there are some - * struct pages which are reserved in memblock allocator and their fields - * may be accessed (for example page_to_pfn() on some configuration accesses - * flags). We must explicitly initialize those struct pages. - * - * This function also addresses a similar issue where struct pages are left - * uninitialized because the physical address range is not covered by - * memblock.memory or memblock.reserved. That could happen when memblock - * layout is manually configured via memmap=, or when the highest physical - * address (max_pfn) does not end on a section boundary. - */ -static void __init init_unavailable_mem(void) -{ - phys_addr_t start, end; - u64 i, pgcnt; - phys_addr_t next = 0; - - /* - * Loop through unavailable ranges not covered by memblock.memory. - */ - pgcnt = 0; - for_each_mem_range(i, &start, &end) { - if (next < start) - pgcnt += init_unavailable_range(PFN_DOWN(next), - PFN_UP(start)); - next = end; - } - - /* - * Early sections always have a fully populated memmap for the whole - * section - see pfn_valid(). If the last section has holes at the - * end and that section is marked "online", the memmap will be - * considered initialized. Make sure that memmap has a well defined - * state. - */ - pgcnt += init_unavailable_range(PFN_DOWN(next), - round_up(max_pfn, PAGES_PER_SECTION)); - - /* - * Struct pages that do not have backing memory. This could be because - * firmware is using some of this memory, or for some other reasons. - */ - if (pgcnt) - pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt); -} -#else -static inline void __init init_unavailable_mem(void) -{ -} -#endif /* !CONFIG_FLAT_NODE_MEM_MAP */ - #if MAX_NUMNODES > 1 /* * Figure out the number of possible node ids. @@ -7597,7 +7579,6 @@ void __init free_area_init(unsigned long *max_zone_pfn) /* Initialise every node */ mminit_verify_pageflags_layout(); setup_nr_node_ids(); - init_unavailable_mem(); for_each_online_node(nid) { pg_data_t *pgdat = NODE_DATA(nid); free_area_init_node(nid);
On 24.02.21 16:39, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } } +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/*
- Only struct pages that correspond to ranges defined by memblock.memory
- are zeroed and initialized by going through __init_single_page() during
- memmap_init_zone().
- But, there could be struct pages that correspond to holes in
- memblock.memory. This can happen because of the following reasons:
- phyiscal memory bank size is not necessarily the exact multiple of the
- arbitrary section size
- early reserved memory may not be listed in memblock.memory
- memory layouts defined with memmap= kernel parameter may not align
- nicely with memmap sections
- Explicitly initialize those struct pages so that:
- PG_Reserved is set
- zone and node links point to zone and node that span the page
- */
+static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,int zone, int node)+{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}__init_single_page(pfn_to_page(pfn), pfn, zone, node);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
+} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
int zone, int node)+{
- return 0;
+} +#endif
- void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- u64 pgcnt = 0;
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
if (hole_pfn < start_pfn)pgcnt += init_unavailable_range(hole_pfn, start_pfn,zone_id, nid);hole_pfn = end_pfn;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);
We might still double-initialize PFNs when two zones overlap within a section, correct? This might worth documenting - also, you might want to take some of the original comment the accompanied this code.
You should also document (in the patch description?) that node/zone spans are not properly handled yet for such hole pfns and that this might require care in the future.
I played a little with weird setups and expected the memap state using page-types (well, I can't inspect the node/zone that way but at least have a look if the memmap was initialized). No surprises.
On Thu, Feb 25, 2021 at 04:59:06PM +0100, David Hildenbrand wrote:
On 24.02.21 16:39, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } } +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/*
- Only struct pages that correspond to ranges defined by memblock.memory
- are zeroed and initialized by going through __init_single_page() during
- memmap_init_zone().
- But, there could be struct pages that correspond to holes in
- memblock.memory. This can happen because of the following reasons:
- phyiscal memory bank size is not necessarily the exact multiple of the
- arbitrary section size
- early reserved memory may not be listed in memblock.memory
- memory layouts defined with memmap= kernel parameter may not align
- nicely with memmap sections
- Explicitly initialize those struct pages so that:
- PG_Reserved is set
- zone and node links point to zone and node that span the page
- */
+static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,int zone, int node)+{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}__init_single_page(pfn_to_page(pfn), pfn, zone, node);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
+} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
int zone, int node)+{
- return 0;
+} +#endif
- void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- u64 pgcnt = 0; for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
@@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
if (hole_pfn < start_pfn)pgcnt += init_unavailable_range(hole_pfn, start_pfn,zone_id, nid);hole_pfn = end_pfn;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);We might still double-initialize PFNs when two zones overlap within a section, correct?
You mean that a section crosses zones boundary? I don't think it's that important.
This might worth documenting - also, you might want to take some of the original comment the accompanied this code.
The original comment was not exactly right, I believe the comment above init_unavailable_range() better describes what's going on there.
You should also document (in the patch description?) that node/zone spans are not properly handled yet for such hole pfns and that this might require care in the future.
I think Link: will suffice for this.
I played a little with weird setups and expected the memap state using page-types (well, I can't inspect the node/zone that way but at least have a look if the memmap was initialized). No surprises.
Great, thanks!
On 25.02.21 18:06, Mike Rapoport wrote:
On Thu, Feb 25, 2021 at 04:59:06PM +0100, David Hildenbrand wrote:
On 24.02.21 16:39, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } } +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/*
- Only struct pages that correspond to ranges defined by memblock.memory
- are zeroed and initialized by going through __init_single_page() during
- memmap_init_zone().
- But, there could be struct pages that correspond to holes in
- memblock.memory. This can happen because of the following reasons:
- phyiscal memory bank size is not necessarily the exact multiple of the
- arbitrary section size
- early reserved memory may not be listed in memblock.memory
- memory layouts defined with memmap= kernel parameter may not align
- nicely with memmap sections
- Explicitly initialize those struct pages so that:
- PG_Reserved is set
- zone and node links point to zone and node that span the page
- */
+static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,int zone, int node)+{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}__init_single_page(pfn_to_page(pfn), pfn, zone, node);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
+} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
int zone, int node)+{
- return 0;
+} +#endif
- void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- u64 pgcnt = 0; for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
@@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
if (hole_pfn < start_pfn)pgcnt += init_unavailable_range(hole_pfn, start_pfn,zone_id, nid);hole_pfn = end_pfn;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);We might still double-initialize PFNs when two zones overlap within a section, correct?
You mean that a section crosses zones boundary? I don't think it's that important.
This might worth documenting - also, you might want to take some of the original comment the accompanied this code.
The original comment was not exactly right, I believe the comment above init_unavailable_range() better describes what's going on there.
Ah, okay - as long as it's documented I'm happy :)
On Thu, Feb 25, 2021 at 9:07 AM Mike Rapoport rppt@linux.ibm.com wrote:
We might still double-initialize PFNs when two zones overlap within a section, correct?
You mean that a section crosses zones boundary? I don't think it's that important.
What if there was a memory allocation in between that could allocate the once-initialized page?
Maybe it can't happen, or is not an issue for some other reason, but this code has been fragile and had a ton of subtle issues, so maybe worth documenting (or explaining here why it's just not relevant)
Linus
On Thu, Feb 25, 2021 at 09:54:34AM -0800, Linus Torvalds wrote:
On Thu, Feb 25, 2021 at 9:07 AM Mike Rapoport rppt@linux.ibm.com wrote:
We might still double-initialize PFNs when two zones overlap within a section, correct?
You mean that a section crosses zones boundary? I don't think it's that important.
What if there was a memory allocation in between that could allocate the once-initialized page?
Can't happen because this code runs before any allocation is possible and it is single threaded.
Maybe it can't happen, or is not an issue for some other reason, but this code has been fragile and had a ton of subtle issues, so maybe worth documenting (or explaining here why it's just not relevant)
Ok, I'll do another pass on the comments in the code.
Linus
On 2/24/21 4:39 PM, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
Hi, thanks for your efforts. I'll just nit pick on the description/comments as I don't feel confident about judging the implementation correctness, sorry :)
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
... in set_pfnblock_flags_mask() when called with a struct page from the "Unknown E820 type" range.
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
I would say "there are apparently pages" ... "and ZONE_DMA does not span this range"
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
What if two zones are adjacent? I.e. if the hole was at a boundary between two zones.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
For the approach: Acked-by: Vlastimil Babka vbabka@suse.cz
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } } +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/*
- Only struct pages that correspond to ranges defined by memblock.memory
- are zeroed and initialized by going through __init_single_page() during
- memmap_init_zone().
- But, there could be struct pages that correspond to holes in
- memblock.memory. This can happen because of the following reasons:
- phyiscal memory bank size is not necessarily the exact multiple of the
physical
- arbitrary section size
- early reserved memory may not be listed in memblock.memory
- memory layouts defined with memmap= kernel parameter may not align
- nicely with memmap sections
- Explicitly initialize those struct pages so that:
- PG_Reserved is set
- zone and node links point to zone and node that span the page
Yes spanned pages are the most important, but should you also describe here the adjacent ones, as you do in commit log?
- */
+static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,int zone, int node)+{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}__init_single_page(pfn_to_page(pfn), pfn, zone, node);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
+} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
int zone, int node)+{
- return 0;
+} +#endif
void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- u64 pgcnt = 0;
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
if (hole_pfn < start_pfn)pgcnt += init_unavailable_range(hole_pfn, start_pfn,zone_id, nid);hole_pfn = end_pfn;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);+#endif
- if (pgcnt)
pr_info(" %s zone: %lld pages in unavailable ranges\n",zone->name, pgcnt);} static int zone_batchsize(struct zone *zone) @@ -7092,88 +7156,6 @@ void __init free_area_init_memoryless_node(int nid) free_area_init_node(nid); } -#if !defined(CONFIG_FLAT_NODE_MEM_MAP) -/*
- Initialize all valid struct pages in the range [spfn, epfn) and mark them
- PageReserved(). Return the number of struct pages that were initialized.
- */
-static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn) -{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}/** Use a fake node/zone (0) for now. Some of these pages* (in memblock.reserved but not in memblock.memory) will* get re-initialized via reserve_bootmem_region() later.*/__init_single_page(pfn_to_page(pfn), pfn, 0, 0);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
-}
-/*
- Only struct pages that are backed by physical memory are zeroed and
- initialized by going through __init_single_page(). But, there are some
- struct pages which are reserved in memblock allocator and their fields
- may be accessed (for example page_to_pfn() on some configuration accesses
- flags). We must explicitly initialize those struct pages.
- This function also addresses a similar issue where struct pages are left
- uninitialized because the physical address range is not covered by
- memblock.memory or memblock.reserved. That could happen when memblock
- layout is manually configured via memmap=, or when the highest physical
- address (max_pfn) does not end on a section boundary.
- */
-static void __init init_unavailable_mem(void) -{
- phys_addr_t start, end;
- u64 i, pgcnt;
- phys_addr_t next = 0;
- /*
* Loop through unavailable ranges not covered by memblock.memory.*/- pgcnt = 0;
- for_each_mem_range(i, &start, &end) {
if (next < start)pgcnt += init_unavailable_range(PFN_DOWN(next),PFN_UP(start));next = end;- }
- /*
* Early sections always have a fully populated memmap for the whole* section - see pfn_valid(). If the last section has holes at the* end and that section is marked "online", the memmap will be* considered initialized. Make sure that memmap has a well defined* state.*/- pgcnt += init_unavailable_range(PFN_DOWN(next),
round_up(max_pfn, PAGES_PER_SECTION));- /*
* Struct pages that do not have backing memory. This could be because* firmware is using some of this memory, or for some other reasons.*/- if (pgcnt)
pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);-} -#else -static inline void __init init_unavailable_mem(void) -{ -} -#endif /* !CONFIG_FLAT_NODE_MEM_MAP */
#if MAX_NUMNODES > 1 /*
- Figure out the number of possible node ids.
@@ -7597,7 +7579,6 @@ void __init free_area_init(unsigned long *max_zone_pfn) /* Initialise every node */ mminit_verify_pageflags_layout(); setup_nr_node_ids();
- init_unavailable_mem(); for_each_online_node(nid) { pg_data_t *pgdat = NODE_DATA(nid); free_area_init_node(nid);
On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote:
On 2/24/21 4:39 PM, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
Hi, thanks for your efforts. I'll just nit pick on the description/comments as I don't feel confident about judging the implementation correctness, sorry :)
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
... in set_pfnblock_flags_mask() when called with a struct page from the "Unknown E820 type" range.
"... in set_pfnblock_flags_mask() when called with a struct page from a range other than E820_TYPE_RAM"
then :)
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
I would say "there are apparently pages" ... "and ZONE_DMA does not span this range"
I'd rephrase it differently, something like
"because there are pages in the range of ZONE_DMA32 but the unset zone link in struct page makes them appear as a part of ZONE_DMA"
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
What if two zones are adjacent? I.e. if the hole was at a boundary between two zones.
What do you mean by "adjacent zones"? If there is a hole near the zone boundary, zone span would be clamped to exclude the hole.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
For the approach: Acked-by: Vlastimil Babka vbabka@suse.cz
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ static void __meminit zone_init_free_lists(struct zone *zone) } } +#if !defined(CONFIG_FLAT_NODE_MEM_MAP) +/*
- Only struct pages that correspond to ranges defined by memblock.memory
- are zeroed and initialized by going through __init_single_page() during
- memmap_init_zone().
- But, there could be struct pages that correspond to holes in
- memblock.memory. This can happen because of the following reasons:
- phyiscal memory bank size is not necessarily the exact multiple of the
physical
Thanks.
- arbitrary section size
- early reserved memory may not be listed in memblock.memory
- memory layouts defined with memmap= kernel parameter may not align
- nicely with memmap sections
- Explicitly initialize those struct pages so that:
- PG_Reserved is set
- zone and node links point to zone and node that span the page
Yes spanned pages are the most important, but should you also describe here the adjacent ones, as you do in commit log?
Will try :)
- */
+static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,int zone, int node)+{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}__init_single_page(pfn_to_page(pfn), pfn, zone, node);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
+} +#else +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
int zone, int node)+{
- return 0;
+} +#endif
void __meminit __weak memmap_init_zone(struct zone *zone) { unsigned long zone_start_pfn = zone->zone_start_pfn; unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- u64 pgcnt = 0;
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) { start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); @@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
if (hole_pfn < start_pfn)pgcnt += init_unavailable_range(hole_pfn, start_pfn,zone_id, nid);hole_pfn = end_pfn;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);+#endif
- if (pgcnt)
pr_info(" %s zone: %lld pages in unavailable ranges\n",zone->name, pgcnt);} static int zone_batchsize(struct zone *zone) @@ -7092,88 +7156,6 @@ void __init free_area_init_memoryless_node(int nid) free_area_init_node(nid); } -#if !defined(CONFIG_FLAT_NODE_MEM_MAP) -/*
- Initialize all valid struct pages in the range [spfn, epfn) and mark them
- PageReserved(). Return the number of struct pages that were initialized.
- */
-static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn) -{
- unsigned long pfn;
- u64 pgcnt = 0;
- for (pfn = spfn; pfn < epfn; pfn++) {
if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)+ pageblock_nr_pages - 1;continue;}/** Use a fake node/zone (0) for now. Some of these pages* (in memblock.reserved but not in memblock.memory) will* get re-initialized via reserve_bootmem_region() later.*/__init_single_page(pfn_to_page(pfn), pfn, 0, 0);__SetPageReserved(pfn_to_page(pfn));pgcnt++;- }
- return pgcnt;
-}
-/*
- Only struct pages that are backed by physical memory are zeroed and
- initialized by going through __init_single_page(). But, there are some
- struct pages which are reserved in memblock allocator and their fields
- may be accessed (for example page_to_pfn() on some configuration accesses
- flags). We must explicitly initialize those struct pages.
- This function also addresses a similar issue where struct pages are left
- uninitialized because the physical address range is not covered by
- memblock.memory or memblock.reserved. That could happen when memblock
- layout is manually configured via memmap=, or when the highest physical
- address (max_pfn) does not end on a section boundary.
- */
-static void __init init_unavailable_mem(void) -{
- phys_addr_t start, end;
- u64 i, pgcnt;
- phys_addr_t next = 0;
- /*
* Loop through unavailable ranges not covered by memblock.memory.*/- pgcnt = 0;
- for_each_mem_range(i, &start, &end) {
if (next < start)pgcnt += init_unavailable_range(PFN_DOWN(next),PFN_UP(start));next = end;- }
- /*
* Early sections always have a fully populated memmap for the whole* section - see pfn_valid(). If the last section has holes at the* end and that section is marked "online", the memmap will be* considered initialized. Make sure that memmap has a well defined* state.*/- pgcnt += init_unavailable_range(PFN_DOWN(next),
round_up(max_pfn, PAGES_PER_SECTION));- /*
* Struct pages that do not have backing memory. This could be because* firmware is using some of this memory, or for some other reasons.*/- if (pgcnt)
pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);-} -#else -static inline void __init init_unavailable_mem(void) -{ -} -#endif /* !CONFIG_FLAT_NODE_MEM_MAP */
#if MAX_NUMNODES > 1 /*
- Figure out the number of possible node ids.
@@ -7597,7 +7579,6 @@ void __init free_area_init(unsigned long *max_zone_pfn) /* Initialise every node */ mminit_verify_pageflags_layout(); setup_nr_node_ids();
- init_unavailable_mem(); for_each_online_node(nid) { pg_data_t *pgdat = NODE_DATA(nid); free_area_init_node(nid);
On 2/25/21 7:05 PM, Mike Rapoport wrote:
On Thu, Feb 25, 2021 at 06:51:53PM +0100, Vlastimil Babka wrote:
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
... in set_pfnblock_flags_mask() when called with a struct page from the "Unknown E820 type" range.
"... in set_pfnblock_flags_mask() when called with a struct page from a range other than E820_TYPE_RAM"
then :)
Better :)
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
I would say "there are apparently pages" ... "and ZONE_DMA does not span this range"
I'd rephrase it differently, something like
"because there are pages in the range of ZONE_DMA32 but the unset zone link in struct page makes them appear as a part of ZONE_DMA"
Much better, thanks!
Interleave initialization of the unavailable pages with the normal initialization of memory map, so that zone and node information will be properly set on struct pages that are not backed by the actual memory.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
What if two zones are adjacent? I.e. if the hole was at a boundary between two zones.
What do you mean by "adjacent zones"? If there is a hole near the zone boundary, zone span would be clamped to exclude the hole.
Yeah, zone span should exclude those pages, but you still somehow handle them? That's how I read "pages that are not spanned by any node will get links to the adjacent zone/node." So is it always a unique zone/node can be determined?
Let's say we have:
<memory on node 0> ---- pageblock boundary ---- <more memory on node 0> <a hole> <memory on node 1> ---- pageblock boundary ----
Now I hope such configurations don't really exist :) But if we simulated them in QEMU, what would be the linkage in struct pages in that hole?
On Thu, Feb 25, 2021 at 07:38:44PM +0100, Vlastimil Babka wrote:
On 2/25/21 7:05 PM, Mike Rapoport wrote:
What if two zones are adjacent? I.e. if the hole was at a boundary between two zones.
What do you mean by "adjacent zones"? If there is a hole near the zone boundary, zone span would be clamped to exclude the hole.
Yeah, zone span should exclude those pages, but you still somehow handle them? That's how I read "pages that are not spanned by any node will get links to the adjacent zone/node." So is it always a unique zone/node can be determined?
Let's say we have:
<memory on node 0> ---- pageblock boundary ---- <more memory on node 0>
<a hole> <memory on node 1> ---- pageblock boundary ----
Now I hope such configurations don't really exist :) But if we simulated them in QEMU, what would be the linkage in struct pages in that hole?
I don't think such configuration is possible in practice but it can be forced with e.g memmap="2M hole at 4G - 1M".
The hole in your example the hole will get node1 for node and zone that spans the beginning of node1 for zone.
On 2/26/21 11:59 AM, Mike Rapoport wrote:
On Thu, Feb 25, 2021 at 07:38:44PM +0100, Vlastimil Babka wrote:
On 2/25/21 7:05 PM, Mike Rapoport wrote:
What if two zones are adjacent? I.e. if the hole was at a boundary between two zones.
What do you mean by "adjacent zones"? If there is a hole near the zone boundary, zone span would be clamped to exclude the hole.
Yeah, zone span should exclude those pages, but you still somehow handle them? That's how I read "pages that are not spanned by any node will get links to the adjacent zone/node." So is it always a unique zone/node can be determined?
Let's say we have:
<memory on node 0> ---- pageblock boundary ---- <more memory on node 0>
<a hole> <memory on node 1> ---- pageblock boundary ----
Now I hope such configurations don't really exist :) But if we simulated them in QEMU, what would be the linkage in struct pages in that hole?
I don't think such configuration is possible in practice but it can be forced with e.g memmap="2M hole at 4G - 1M".
Right.
The hole in your example the hole will get node1 for node and zone that spans the beginning of node1 for zone.
Yeah the comments in v8 make that clear now, thanks!
linux-stable-mirror@lists.linaro.org
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