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mm/hugetlb: update nr_huge_pages and surplus_huge_pages together

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In alloc_surplus_hugetlb_folio(), we increase nr_huge_pages and
surplus_huge_pages separately.  In the middle window, if we set
nr_hugepages to smaller and satisfy count < persistent_huge_pages(h), the
surplus_huge_pages will be increased by adjust_pool_surplus().

After adding delay in the middle window, we can reproduce the problem
easily by following step:

 1. echo 3 > /proc/sys/vm/nr_overcommit_hugepages
 2. mmap two hugepages. When nr_huge_pages=2 and surplus_huge_pages=1,
    goto step 3.
 3. echo 0 > /proc/sys/vm/nr_huge_pages

Finally, nr_huge_pages is less than surplus_huge_pages.

To fix the problem, call only_alloc_fresh_hugetlb_folio() instead and
move down __prep_account_new_huge_page() into the hugetlb_lock.

Link: https://lkml.kernel.org/r/20250305035409.2391344-1-liushixin2@huawei.com
Fixes: 0c397daea1 ("mm, hugetlb: further simplify hugetlb allocation API")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liu Shixin 2025-03-05 11:54:09 +08:00 committed by Andrew Morton
parent 114b480877
commit 2273dea6b1
1 changed files with 10 additions and 1 deletions
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11
mm/hugetlb.c
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@ -2259,11 +2259,20 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
goto out_unlock;
spin_unlock_irq(&hugetlb_lock);
folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
if (!folio)
return NULL;
hugetlb_vmemmap_optimize_folio(h, folio);
spin_lock_irq(&hugetlb_lock);
/*
* nr_huge_pages needs to be adjusted within the same lock cycle
* as surplus_pages, otherwise it might confuse
* persistent_huge_pages() momentarily.
*/
__prep_account_new_huge_page(h, nid);
/*
* We could have raced with the pool size change.
* Double check that and simply deallocate the new page