From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Fixes: b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages") Signed-off-by: Ge Yang yangge1116@126.com --- include/linux/hugetlb.h | 5 +++++ mm/hugetlb.c | 7 +++++++ mm/migrate.c | 16 ++++++++++++++-- 3 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 6c6546b..c39e0d5 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -697,6 +697,7 @@ bool hugetlb_bootmem_page_zones_valid(int nid, struct huge_bootmem_page *m);
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); +void wait_for_hugepage_folios_freed(struct hstate *h); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, bool cow_from_owner); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1092,6 +1093,10 @@ static inline int replace_free_hugepage_folios(unsigned long start_pfn, return 0; }
+static inline void wait_for_hugepage_folios_freed(struct hstate *h) +{ +} + static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, bool cow_from_owner) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 30bc34d..64cae39 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2955,6 +2955,13 @@ int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) return ret; }
+void wait_for_hugepage_folios_freed(struct hstate *h) +{ + WARN_ON(!h); + + flush_free_hpage_work(h); +} + typedef enum { /* * For either 0/1: we checked the per-vma resv map, and one resv diff --git a/mm/migrate.c b/mm/migrate.c index fb19a18..5dd1851 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1448,6 +1448,7 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, int page_was_mapped = 0; struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; + unsigned long size;
if (folio_ref_count(src) == 1) { /* page was freed from under us. So we are done. */ @@ -1533,9 +1534,20 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, out_unlock: folio_unlock(src); out: - if (rc == MIGRATEPAGE_SUCCESS) + if (rc == MIGRATEPAGE_SUCCESS) { + size = folio_size(src); folio_putback_hugetlb(src); - else if (rc != -EAGAIN) + + /* + * Due to the deferred freeing of HugeTLB folios, the hugepage 'src' may + * not immediately release to the buddy system. This can lead to failure + * in allocating memory through the cma_alloc() function. To ensure that + * the hugepage folios are properly released back to the buddy system, + * we invoke the wait_for_hugepage_folios_freed() function to wait for + * the release to complete. + */ + wait_for_hugepage_folios_freed(size_to_hstate(size)); + } else if (rc != -EAGAIN) list_move_tail(&src->lru, ret);
/*
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] mm/hugetlb: wait for hugepage folios to be freed Link: https://lore.kernel.org/stable/1739514729-21265-1-git-send-email-yangge1116%...
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
I wonder if that waiting should instead be done exactly once after migrating multiple folios? For example, at the beginning of test_pages_isolated(), to "flush" that state from any previous migration?
Thanks for all your effort around making CMA allocations / migration more reliable.
在 2025/2/14 16:08, David Hildenbrand 写道:
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
It seems that we only track unmovable, reclaimable, and movable pages on the pcp lists. For specific details, please refer to the free_frozen_pages() function.
I wonder if that waiting should instead be done exactly once after migrating multiple folios? For example, at the beginning of test_pages_isolated(), to "flush" that state from any previous migration?
Yes, this can improve performance. I will make the modification in the next version. Thank you.
Thanks for all your effort around making CMA allocations / migration more reliable.
On 15.02.25 06:50, Ge Yang wrote:
在 2025/2/14 16:08, David Hildenbrand 写道:
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
It seems that we only track unmovable, reclaimable, and movable pages on the pcp lists. For specific details, please refer to the free_frozen_pages() function.
It reminded me about PCP caches, because we effectively also have to wait for some stuck folios to properly get freed to the buddy.
在 2025/2/18 16:55, David Hildenbrand 写道:
On 15.02.25 06:50, Ge Yang wrote:
在 2025/2/14 16:08, David Hildenbrand 写道:
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
It seems that we only track unmovable, reclaimable, and movable pages on the pcp lists. For specific details, please refer to the free_frozen_pages() function.
It reminded me about PCP caches, because we effectively also have to wait for some stuck folios to properly get freed to the buddy.
It seems that when an isolated page is freed, it won't be placed back into the PCP caches.
On 18.02.25 10:22, Ge Yang wrote:
在 2025/2/18 16:55, David Hildenbrand 写道:
On 15.02.25 06:50, Ge Yang wrote:
在 2025/2/14 16:08, David Hildenbrand 写道:
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
It seems that we only track unmovable, reclaimable, and movable pages on the pcp lists. For specific details, please refer to the free_frozen_pages() function.
It reminded me about PCP caches, because we effectively also have to wait for some stuck folios to properly get freed to the buddy.
It seems that when an isolated page is freed, it won't be placed back into the PCP caches.
I recall there are cases when the page was in the pcp before the isolation started, which is why we drain the pcp at some point (IIRC).
在 2025/2/18 17:41, David Hildenbrand 写道:
On 18.02.25 10:22, Ge Yang wrote:
在 2025/2/18 16:55, David Hildenbrand 写道:
On 15.02.25 06:50, Ge Yang wrote:
在 2025/2/14 16:08, David Hildenbrand 写道:
On 14.02.25 07:32, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.com
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages"), which supports deferring the freeing of HugeTLB pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.
In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugepage folios, these in-use hugepage folios need to be migrated to another location. When there are no available hugepage folios in the free HugeTLB pool during the migration of in-use HugeTLB pages, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugepage folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of HugeTLB pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().
Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugepage ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy
To resolve this issue, we have implemented a function named wait_for_hugepage_folios_freed(). This function ensures that the hugepage folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_hugepage_folios_freed() following the migration process, we guarantee that when test_pages_isolated() is executed, it will successfully pass.
Okay, so after every successful migration -> put of src, we wait for the src to actually get freed.
When migrating multiple hugetlb folios, we'd wait once per folio.
It reminds me a bit about pcp caches, where folios are !buddy until the pcp was drained.
It seems that we only track unmovable, reclaimable, and movable pages on the pcp lists. For specific details, please refer to the free_frozen_pages() function.
It reminded me about PCP caches, because we effectively also have to wait for some stuck folios to properly get freed to the buddy.
It seems that when an isolated page is freed, it won't be placed back into the PCP caches.
I recall there are cases when the page was in the pcp before the isolation started, which is why we drain the pcp at some point (IIRC).
Yes, indeed, drain_all_pages(cc.zone) is currently executed before __alloc_contig_migrate_range().
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