From: yangge yangge1116@126.com
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
To address this issue, we will add a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke the replace_free_hugepage_folios() function to ensure that these hugepages are properly released to the buddy system. Following this step, when the test_pages_isolated() function is executed for inspection, it will successfully pass.
Signed-off-by: yangge yangge1116@126.com --- include/linux/hugetlb.h | 6 ++++++ mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 13 ++++++++++++- 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { };
int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; }
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + return 0; +} + static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8e1db80..a099c54 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list) return ret; }
+/* + * replace_free_hugepage_folios - Replace free hugepage folios in a given pfn + * range with new folios. + * @stat_pfn: start pfn of the given pfn range + * @end_pfn: end pfn of the given pfn range + * Returns 0 on success, otherwise negated error. + */ +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + struct hstate *h; + struct folio *folio; + int ret = 0; + + LIST_HEAD(isolate_list); + + while (start_pfn < end_pfn) { + folio = pfn_folio(start_pfn); + if (folio_test_hugetlb(folio)) { + h = folio_hstate(folio); + } else { + start_pfn++; + continue; + } + + if (!folio_ref_count(folio)) { + ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list); + if (ret) + break; + + putback_movable_pages(&isolate_list); + } + start_pfn++; + } + + return ret; +} + struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..1dcea28 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, ret = __alloc_contig_migrate_range(&cc, start, end, migratetype); if (ret && ret != -EBUSY) goto done; - ret = 0; + + /* + * When in-use hugetlb pages are migrated, they may simply be + * released back into the free hugepage pool instead of being + * returned to the buddy system. After the migration of in-use + * huge pages is completed, we will invoke the + * replace_free_hugepage_folios() function to ensure that + * these hugepages are properly released to the buddy system. + */ + ret = replace_free_hugepage_folios(start, end); + if (ret) + goto done;
/* * Pages from [start, end) are within a pageblock_nr_pages
Hi,
Thanks for your patch.
FYI: kernel test robot notices the stable kernel rule is not satisfied.
The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#opti...
Rule: add the tag "Cc: stable@vger.kernel.org" in the sign-off area to have the patch automatically included in the stable tree. Subject: [PATCH] replace free hugepage folios after migration Link: https://lore.kernel.org/stable/1734503588-16254-1-git-send-email-yangge1116%...
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
To address this issue, we will add a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke the replace_free_hugepage_folios() function to ensure that these hugepages are properly released to the buddy system. Following this step, when the test_pages_isolated() function is executed for inspection, it will successfully pass.
Signed-off-by: yangge yangge1116@126.com
include/linux/hugetlb.h | 6 ++++++ mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 13 ++++++++++++- 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- return 0;
+}
- static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8e1db80..a099c54 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list) return ret; } +/*
- replace_free_hugepage_folios - Replace free hugepage folios in a given pfn
- range with new folios.
- @stat_pfn: start pfn of the given pfn range
- @end_pfn: end pfn of the given pfn range
- Returns 0 on success, otherwise negated error.
- */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- struct hstate *h;
- struct folio *folio;
- int ret = 0;
- LIST_HEAD(isolate_list);
- while (start_pfn < end_pfn) {
folio = pfn_folio(start_pfn);if (folio_test_hugetlb(folio)) {h = folio_hstate(folio);} else {start_pfn++;continue;}if (!folio_ref_count(folio)) {ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list);if (ret)break;putback_movable_pages(&isolate_list);}start_pfn++;- }
- return ret;
+}
- struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..1dcea28 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, ret = __alloc_contig_migrate_range(&cc, start, end, migratetype); if (ret && ret != -EBUSY) goto done;
- ret = 0;
- /*
* When in-use hugetlb pages are migrated, they may simply be* released back into the free hugepage pool instead of being* returned to the buddy system. After the migration of in-use* huge pages is completed, we will invoke the* replace_free_hugepage_folios() function to ensure that* these hugepages are properly released to the buddy system.*/- ret = replace_free_hugepage_folios(start, end);
- if (ret)
goto done;/* * Pages from [start, end) are within a pageblock_nr_pages
在 2024/12/20 0:40, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
After migration, in-use hugetlb pages are only released back to the hugetlb pool and are not returned to the buddy system.
The specific steps for reproduction are as follows: 1，Reserve hugetlb pages. Some of these hugetlb pages are allocated within the CMA area. echo 10240 > /proc/sys/vm/nr_hugepages
2，To ensure that hugetlb pages are in an in-use state, we can use the following command. qemu-system-x86_64 \ -mem-prealloc \ -mem-path /dev/hugepage/ \ ...
3，At this point, using cma_alloc() to allocate contiguous memory may result in a probable failure.
To address this issue, we will add a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke the replace_free_hugepage_folios() function to ensure that these hugepages are properly released to the buddy system. Following this step, when the test_pages_isolated() function is executed for inspection, it will successfully pass.
Signed-off-by: yangge yangge1116@126.com
include/linux/hugetlb.h | 6 ++++++ mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 13 ++++++++++++- 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + return 0; +}
static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8e1db80..a099c54 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list) return ret; } +/*
- * replace_free_hugepage_folios - Replace free hugepage folios in a
given pfn
- * range with new folios.
- * @stat_pfn: start pfn of the given pfn range
- * @end_pfn: end pfn of the given pfn range
- * Returns 0 on success, otherwise negated error.
- */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + struct hstate *h; + struct folio *folio; + int ret = 0;
+ LIST_HEAD(isolate_list);
+ while (start_pfn < end_pfn) { + folio = pfn_folio(start_pfn); + if (folio_test_hugetlb(folio)) { + h = folio_hstate(folio); + } else { + start_pfn++; + continue; + }
+ if (!folio_ref_count(folio)) { + ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list); + if (ret) + break;
+ putback_movable_pages(&isolate_list); + } + start_pfn++; + }
+ return ret; +}
struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..1dcea28 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, ret = __alloc_contig_migrate_range(&cc, start, end, migratetype); if (ret && ret != -EBUSY) goto done; - ret = 0;
+ /* + * When in-use hugetlb pages are migrated, they may simply be + * released back into the free hugepage pool instead of being + * returned to the buddy system. After the migration of in-use + * huge pages is completed, we will invoke the + * replace_free_hugepage_folios() function to ensure that + * these hugepages are properly released to the buddy system. + */ + ret = replace_free_hugepage_folios(start, end); + if (ret) + goto done; /* * Pages from [start, end) are within a pageblock_nr_pages
On 20.12.24 09:56, Ge Yang wrote:
在 2024/12/20 0:40, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
After migration, in-use hugetlb pages are only released back to the hugetlb pool and are not returned to the buddy system.
We had
commit ae37c7ff79f1f030e28ec76c46ee032f8fd07607 Author: Oscar Salvador osalvador@suse.de Date: Tue May 4 18:35:29 2021 -0700
mm: make alloc_contig_range handle in-use hugetlb pages
alloc_contig_range() will fail if it finds a HugeTLB page within the range, without a chance to handle them. Since HugeTLB pages can be migrated as any LRU or Movable page, it does not make sense to bail out without trying. Enable the interface to recognize in-use HugeTLB pages so we can migrate them, and have much better chances to succeed the call.
And I am trying to figure out if it never worked correctly, or if something changed that broke it.
In start_isolate_page_range()->isolate_migratepages_block(), we do the
ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
to add these folios to the cc->migratepages list.
In __alloc_contig_migrate_range(), we migrate the pages using migrate_pages().
After that, the src hugetlb folios should still be isolated? But I'm getting confused when these pages get un-silated and putback to hugetlb/freed.
The specific steps for reproduction are as follows: 1，Reserve hugetlb pages. Some of these hugetlb pages are allocated within the CMA area. echo 10240 > /proc/sys/vm/nr_hugepages
2，To ensure that hugetlb pages are in an in-use state, we can use the following command. qemu-system-x86_64 \ -mem-prealloc \ -mem-path /dev/hugepage/ \ ...
3，At this point, using cma_alloc() to allocate contiguous memory may result in a probable failure.
Will these free hugetlb folios become surplus pages? I would have assumed they get freed immediately to the buddy, or does you config maybe allow for surplus pages?
在 2024/12/21 0:30, David Hildenbrand 写道:
On 20.12.24 09:56, Ge Yang wrote:
在 2024/12/20 0:40, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
After migration, in-use hugetlb pages are only released back to the hugetlb pool and are not returned to the buddy system.
We had
commit ae37c7ff79f1f030e28ec76c46ee032f8fd07607 Author: Oscar Salvador osalvador@suse.de Date: Tue May 4 18:35:29 2021 -0700
mm: make alloc_contig_range handle in-use hugetlb pages alloc_contig_range() will fail if it finds a HugeTLB page within the range, without a chance to handle them. Since HugeTLB pages can be migrated as any LRU or Movable page, it does not make sense to bail out without trying. Enable the interface to recognize in-use HugeTLB pages so we can migrate them, and have much better chances to succeed the call.
And I am trying to figure out if it never worked correctly, or if something changed that broke it.
In start_isolate_page_range()->isolate_migratepages_block(), we do the
ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
to add these folios to the cc->migratepages list.
In __alloc_contig_migrate_range(), we migrate the pages using migrate_pages().
After that, the src hugetlb folios should still be isolated?
Yes.
But I'm
getting confused when these pages get un-silated and putback to hugetlb/freed.
If the migration is successful, call folio_putback_active_hugetlb to release the src hugetlb folios back to the free hugetlb pool.
trace: unmap_and_move_huge_page folio_putback_active_hugetlb folio_put free_huge_folio
alloc_contig_range_noprof __alloc_contig_migrate_range if (test_pages_isolated()) //to determine if hugetlb pages in buddy isolate_freepages_range //grab isolated pages from freelists. else undo_isolate_page_range //undo isolate
The specific steps for reproduction are as follows: 1，Reserve hugetlb pages. Some of these hugetlb pages are allocated within the CMA area. echo 10240 > /proc/sys/vm/nr_hugepages
2，To ensure that hugetlb pages are in an in-use state, we can use the following command. qemu-system-x86_64 \ -mem-prealloc \ -mem-path /dev/hugepage/ \ ...
3，At this point, using cma_alloc() to allocate contiguous memory may result in a probable failure.
Will these free hugetlb folios become surplus pages? I would have assumed they get freed immediately to the buddy, or does you config maybe allow for surplus pages?
These freed hugetlb folios will not become surplus pages. I have not configured the system to allow for the existence of surplus pages.
On 21.12.24 13:04, Ge Yang wrote:
在 2024/12/21 0:30, David Hildenbrand 写道:
On 20.12.24 09:56, Ge Yang wrote:
在 2024/12/20 0:40, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
After migration, in-use hugetlb pages are only released back to the hugetlb pool and are not returned to the buddy system.
We had
commit ae37c7ff79f1f030e28ec76c46ee032f8fd07607 Author: Oscar Salvador osalvador@suse.de Date: Tue May 4 18:35:29 2021 -0700
mm: make alloc_contig_range handle in-use hugetlb pages alloc_contig_range() will fail if it finds a HugeTLB page within the range, without a chance to handle them. Since HugeTLB pages can be migrated as any LRU or Movable page, it does not make sense to bail out without trying. Enable the interface to recognize in-use HugeTLB pages so we can migrate them, and have much better chances to succeed the call.
And I am trying to figure out if it never worked correctly, or if something changed that broke it.
In start_isolate_page_range()->isolate_migratepages_block(), we do the
ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
to add these folios to the cc->migratepages list.
In __alloc_contig_migrate_range(), we migrate the pages using migrate_pages().
After that, the src hugetlb folios should still be isolated?
Yes.
But I'm
getting confused when these pages get un-silated and putback to hugetlb/freed.
If the migration is successful, call folio_putback_active_hugetlb to release the src hugetlb folios back to the free hugetlb pool.
trace: unmap_and_move_huge_page folio_putback_active_hugetlb folio_put free_huge_folio
alloc_contig_range_noprof __alloc_contig_migrate_range if (test_pages_isolated()) //to determine if hugetlb pages in buddy isolate_freepages_range //grab isolated pages from freelists. else undo_isolate_page_range //undo isolate
Ah, now I remember, thanks.
So when we free an ordinary page, we put it onto the buddy isolate list, from where we can grab it later and nobody can allocate it in the meantime.
In case of hugetlb, we simply free it back to hugetlb, from where it can likely even get allocated immediately again.
I think that can actually happen in your proposal: the now-free page will get reallocated, for example for migrating the next folio. Or some concurrent system activity can simply allocate the now-free folio. Or am I missing something that prevents these now-free hugetlb folios from getting re-allocated after migration succeeded?
Conceptually, I think we would want migration code in the case of alloc_contig_range() to allocate a new folio from the buddy, and to free the old one back to the buddy immediately, without ever allowing re-allocation of it.
What needs to be handled is detecting that
(a) we want to allocate a fresh hugetlb folio as migration target (b) if migration succeeds, we have to free the hugetlb folio back to the buddy (c) if migation fails, we have to free the allocated hugetlb foliio back to the buddy
We could provide a custom alloc_migration_target that we pass to migrate_page to allocate a fresh hugetlb folio to handle (a). Using the put_new_folio callback we could handle (c). (b) would need some thought.
Maybe we can also just mark the source folio as we isolate it, and enlighten migration+freeing code to handle it automatically?
Hoping to get some feedback from hugetlb maintainers.
在 2024/12/21 22:32, David Hildenbrand 写道:
On 21.12.24 13:04, Ge Yang wrote:
在 2024/12/21 0:30, David Hildenbrand 写道:
On 20.12.24 09:56, Ge Yang wrote:
在 2024/12/20 0:40, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
CCing Oscar, who worked on migrating these pages during memory offlining and alloc_contig_range().
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
I thought this would be working as expected, at least we tested it with alloc_contig_range / virtio-mem a while ago.
On the memory_offlining path, we migrate hugetlb folios, but also dissolve any remaining free folios even if it means that we will going below the requested number of hugetlb pages in our pool.
During alloc_contig_range(), we only migrate them, to then free them up after migration.
Under which circumstances doe sit apply that "they may simply be released back into the free hugepage pool instead of being returned to the buddy system"?
After migration, in-use hugetlb pages are only released back to the hugetlb pool and are not returned to the buddy system.
We had
commit ae37c7ff79f1f030e28ec76c46ee032f8fd07607 Author: Oscar Salvador osalvador@suse.de Date: Tue May 4 18:35:29 2021 -0700
mm: make alloc_contig_range handle in-use hugetlb pages alloc_contig_range() will fail if it finds a HugeTLB page within the range, without a chance to handle them. Since HugeTLB pages can be migrated as any LRU or Movable page, it does not make sense to bail out without trying. Enable the interface to recognize in-use HugeTLB pages so we can migrate them, and have much better chances to succeed the call.
And I am trying to figure out if it never worked correctly, or if something changed that broke it.
In start_isolate_page_range()->isolate_migratepages_block(), we do the
ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
to add these folios to the cc->migratepages list.
In __alloc_contig_migrate_range(), we migrate the pages using migrate_pages().
After that, the src hugetlb folios should still be isolated?
Yes.
But I'm
getting confused when these pages get un-silated and putback to hugetlb/freed.
If the migration is successful, call folio_putback_active_hugetlb to release the src hugetlb folios back to the free hugetlb pool.
trace: unmap_and_move_huge_page folio_putback_active_hugetlb folio_put free_huge_folio
alloc_contig_range_noprof __alloc_contig_migrate_range if (test_pages_isolated()) //to determine if hugetlb pages in buddy isolate_freepages_range //grab isolated pages from freelists. else undo_isolate_page_range //undo isolate
Ah, now I remember, thanks.
So when we free an ordinary page, we put it onto the buddy isolate list, from where we can grab it later and nobody can allocate it in the meantime.
In case of hugetlb, we simply free it back to hugetlb, from where it can likely even get allocated immediately again.
I think that can actually happen in your proposal: the now-free page will get reallocated, for example for migrating the next folio. Or some concurrent system activity can simply allocate the now-free folio. Or am I missing something that prevents these now-free hugetlb folios from getting re-allocated after migration succeeded?
Conceptually, I think we would want migration code in the case of alloc_contig_range() to allocate a new folio from the buddy, and to free the old one back to the buddy immediately, without ever allowing re- allocation of it.
What needs to be handled is detecting that
(a) we want to allocate a fresh hugetlb folio as migration target (b) if migration succeeds, we have to free the hugetlb folio back to the buddy (c) if migation fails, we have to free the allocated hugetlb foliio back to the buddy
We could provide a custom alloc_migration_target that we pass to migrate_page to allocate a fresh hugetlb folio to handle (a). Using the put_new_folio callback we could handle (c). (b) would need some thought.
It seems that if we allocate a fresh hugetlb folio as the migration target, the source hugetlb folio will be automatically released back to the buddy system.
Maybe we can also just mark the source folio as we isolate it, and enlighten migration+freeing code to handle it automatically?
Can we determine whether a hugetlb page is isolated when allocating it from the free hugetlb pool?
dequeue_hugetlb_folio_node_exact() { list_for_each_entry(folio, &h->hugepage_freelists[nid], lru) { if (is_migrate_isolate_page(folio)) { //determine whether a hugetlb page is isolated continue; } } }
Hoping to get some feedback from hugetlb maintainers.
Hello,
On Wed, 18 Dec 2024 14:33:08 +0800 yangge1116@126.com wrote:
[...]
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- return 0;
+}
I think this should be static inline. Otherwise, build fails when CONFIG_HUGETLB_PAGE is unset. Since this is already merged into mm-unstable and the problem and fix seems straigthforward, I directly sent my fix: https://lore.kernel.org/20241219183753.62922-1-sj@kernel.org
Thanks, SJ
[...]
在 2024/12/20 2:43, SeongJae Park 写道:
Hello,
On Wed, 18 Dec 2024 14:33:08 +0800 yangge1116@126.com wrote:
[...]
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- return 0;
+}
I think this should be static inline. Otherwise, build fails when CONFIG_HUGETLB_PAGE is unset. Since this is already merged into mm-unstable and the problem and fix seems straigthforward, I directly sent my fix: https://lore.kernel.org/20241219183753.62922-1-sj@kernel.org
Thanks, SJ
[...]
Thanks.
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
To address this issue, we will add a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke the replace_free_hugepage_folios() function to ensure that these hugepages are properly released to the buddy system. Following this step, when the test_pages_isolated() function is executed for inspection, it will successfully pass.
Signed-off-by: yangge yangge1116@126.com
include/linux/hugetlb.h | 6 ++++++ mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 13 ++++++++++++- 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- return 0;
+}
- static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8e1db80..a099c54 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list) return ret; } +/*
- replace_free_hugepage_folios - Replace free hugepage folios in a given pfn
- range with new folios.
- @stat_pfn: start pfn of the given pfn range
- @end_pfn: end pfn of the given pfn range
- Returns 0 on success, otherwise negated error.
- */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{
- struct hstate *h;
- struct folio *folio;
- int ret = 0;
- LIST_HEAD(isolate_list);
- while (start_pfn < end_pfn) {
folio = pfn_folio(start_pfn);if (folio_test_hugetlb(folio)) {h = folio_hstate(folio);} else {start_pfn++;continue;}if (!folio_ref_count(folio)) {ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list);if (ret)break;putback_movable_pages(&isolate_list);}start_pfn++;- }
- return ret;
+}
- struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..1dcea28 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, ret = __alloc_contig_migrate_range(&cc, start, end, migratetype); if (ret && ret != -EBUSY) goto done;
- ret = 0;
- /*
* When in-use hugetlb pages are migrated, they may simply be* released back into the free hugepage pool instead of being* returned to the buddy system. After the migration of in-use* huge pages is completed, we will invoke the* replace_free_hugepage_folios() function to ensure that* these hugepages are properly released to the buddy system.*/
As mentioned in my other mail, what I don't like about this is, IIUC, the pages can get reallocated anytime after we successfully migrated them, or is there anything that prevents that?
Did you ever try allocating a larger range with a single alloc_contig_range() call, that possibly has to migrate multiple hugetlb folios in one go (and maybe just allocates one of the just-freed hugetlb folios as migration target)?
在 2024/12/21 22:35, David Hildenbrand 写道:
On 18.12.24 07:33, yangge1116@126.com wrote:
From: yangge yangge1116@126.com
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via the cma_alloc() function can fail probabilistically.
The cma_alloc() function may fail if it sees an in-use hugetlb page within the allocation range, even if that page has already been migrated. When in-use hugetlb pages are migrated, they may simply be released back into the free hugepage pool instead of being returned to the buddy system. This can cause the test_pages_isolated() function check to fail, ultimately leading to the failure of the cma_alloc() function: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy
To address this issue, we will add a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke the replace_free_hugepage_folios() function to ensure that these hugepages are properly released to the buddy system. Following this step, when the test_pages_isolated() function is executed for inspection, it will successfully pass.
Signed-off-by: yangge yangge1116@126.com
include/linux/hugetlb.h | 6 ++++++ mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 13 ++++++++++++- 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ae4fe86..7d36ac8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -681,6 +681,7 @@ struct huge_bootmem_page { }; int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page, return -ENOMEM; } +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + return 0; +}
static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8e1db80..a099c54 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list) return ret; } +/*
- * replace_free_hugepage_folios - Replace free hugepage folios in a
given pfn
- * range with new folios.
- * @stat_pfn: start pfn of the given pfn range
- * @end_pfn: end pfn of the given pfn range
- * Returns 0 on success, otherwise negated error.
- */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) +{ + struct hstate *h; + struct folio *folio; + int ret = 0;
+ LIST_HEAD(isolate_list);
+ while (start_pfn < end_pfn) { + folio = pfn_folio(start_pfn); + if (folio_test_hugetlb(folio)) { + h = folio_hstate(folio); + } else { + start_pfn++; + continue; + }
+ if (!folio_ref_count(folio)) { + ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list); + if (ret) + break;
+ putback_movable_pages(&isolate_list); + } + start_pfn++; + }
+ return ret; +}
struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve) { diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..1dcea28 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end, ret = __alloc_contig_migrate_range(&cc, start, end, migratetype); if (ret && ret != -EBUSY) goto done; - ret = 0;
+ /* + * When in-use hugetlb pages are migrated, they may simply be + * released back into the free hugepage pool instead of being + * returned to the buddy system. After the migration of in-use + * huge pages is completed, we will invoke the + * replace_free_hugepage_folios() function to ensure that + * these hugepages are properly released to the buddy system. + */
As mentioned in my other mail, what I don't like about this is, IIUC, the pages can get reallocated anytime after we successfully migrated them, or is there anything that prevents that?
The pages can get reallocated anytime after we successfully migrated them. Currently, I haven't thought of a good way to prevent it.
Did you ever try allocating a larger range with a single alloc_contig_range() call, that possibly has to migrate multiple hugetlb folios in one go (and maybe just allocates one of the just-freed hugetlb folios as migration target)?
I have tried using a single alloc_contig_range() call to allocate a larger contiguous range, and it works properly. This is because during the period between __alloc_contig_migrate_range() and isolate_freepages_range(), no one allocates a hugetlb folio from the free hugetlb pool.
Sorry for the late reply, holidays ...
Did you ever try allocating a larger range with a single alloc_contig_range() call, that possibly has to migrate multiple hugetlb folios in one go (and maybe just allocates one of the just-freed hugetlb folios as migration target)?
I have tried using a single alloc_contig_range() call to allocate a larger contiguous range, and it works properly. This is because during the period between __alloc_contig_migrate_range() and isolate_freepages_range(), no one allocates a hugetlb folio from the free hugetlb pool.
Did you trigger the following as well?
alloc_contig_range() that covers multiple in-use hugetlb pages, like
[ huge 0 ] [ huge 1 ] [ huge 2 ] [ huge 3 ]
I assume the following happens:
To migrate huge 0, we have to allocate a fresh page from the buddy. After migration, we return now-free huge 0 to the pool.
To migrate huge 1, we can just grab now-free huge 0 from the pool, and not allocate a fresh one from the buddy.
At least that's my impression when reading alloc_migration_target()->alloc_hugetlb_folio_nodemask().
Or is for some reason available_huge_pages()==false and we always end up in alloc_migrate_hugetlb_folio()->alloc_fresh_hugetlb_folio()?
Sorry for the stupid questions, the code is complicated, and I cannot see how this would work.
在 2025/1/9 5:05, David Hildenbrand 写道:
Sorry for the late reply, holidays ...
Did you ever try allocating a larger range with a single alloc_contig_range() call, that possibly has to migrate multiple hugetlb folios in one go (and maybe just allocates one of the just-freed hugetlb folios as migration target)?
I have tried using a single alloc_contig_range() call to allocate a larger contiguous range, and it works properly. This is because during the period between __alloc_contig_migrate_range() and isolate_freepages_range(), no one allocates a hugetlb folio from the free hugetlb pool.
Did you trigger the following as well?
alloc_contig_range() that covers multiple in-use hugetlb pages, like
[ huge 0 ] [ huge 1 ] [ huge 2 ] [ huge 3 ]
I assume the following happens:
To migrate huge 0, we have to allocate a fresh page from the buddy. After migration, we return now-free huge 0 to the pool.
To migrate huge 1, we can just grab now-free huge 0 from the pool, and not allocate a fresh one from the buddy.
At least that's my impression when reading alloc_migration_target()-
alloc_hugetlb_folio_nodemask().
Thank you very much for your suggestions.
It needs to be discussed in two different scenarios:
1, When All Free HugeTLB Pages in the Pool Are Allocated, available_huge_page() Returns false
If available_huge_page() returns false, indicating that no free huge pages are available in the hugeTLB pool, we will invoke alloc_migrate_hugetlb_folio() to allocate a new folio. A temporary flag will be set on this new folio. After the migration of the hugeTLB folio is completed, the temporary flag will be transferred from the new folio to the old one. Any folio with the temporary flag, when freed, will be directly released to the buddy allocator.
2, When Some Free HugeTLB Pages in the Pool Are Still Available, available_huge_page() Returns true
If available_huge_page() returns true, indicating that there are still free huge pages available in the hugeTLB pool, we will call dequeue_hugetlb_folio_node() to allocate a new folio. After the migration of the hugeTLB folio is completed, the old folio will be released back to the free hugeTLB pool. However, this scenario may pose potential issues, as you mentioned earlier. It seems that the issue can be resolved by the following approach:
dequeue_hugetlb_folio_node_exact() { list_for_each_entry(folio, &h->hugepage_freelists[nid], lru) { if (is_migrate_isolate_page(folio)) { //determine whether a hugetlb page is isolated continue; } } }
Or is for some reason available_huge_pages()==false and we always end up in alloc_migrate_hugetlb_folio()->alloc_fresh_hugetlb_folio()?
Sorry for the stupid questions, the code is complicated, and I cannot see how this would work.
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