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madvise:madvise_free_huge_pmd(): don't use mapcount() against large folio for sharing check

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Commit fc986a38b6 ("mm: huge_memory: convert madvise_free_huge_pmd to
use a folio") replaced the page_mapcount() with folio_mapcount() to check
whether the folio is shared by other mapping.

It's not correct for large folios. folio_mapcount() returns the total
mapcount of large folio which is not suitable to detect whether the folio
is shared.

Use folio_estimated_sharers() which returns a estimated number of shares.
That means it's not 100% correct. It should be OK for madvise case here.

User-visible effects is that the THP is skipped when user call madvise.
But the correct behavior is THP should be split and processed then.

NOTE: this change is a temporary fix to reduce the user-visible effects
before the long term fix from David is ready.

Link: https://lkml.kernel.org/r/20230808020917.2230692-3-fengwei.yin@intel.com
Fixes: fc986a38b6 ("mm: huge_memory: convert madvise_free_huge_pmd to use a folio")
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yin Fengwei 2023-08-08 10:09:16 +08:00 committed by Andrew Morton
parent 2f406263e3
commit 20b18aada1
1 changed files with 1 additions and 1 deletions
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2
mm/huge_memory.c
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@ -1612,7 +1612,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
* If other processes are mapping this folio, we couldn't discard
* the folio unless they all do MADV_FREE so let's skip the folio.
*/
if (folio_mapcount(folio) != 1)
if (folio_estimated_sharers(folio) != 1)
goto out;
if (!folio_trylock(folio))