Patch series "don't use mapcount() to check large folio sharing", v2.

In madvise_cold_or_pageout_pte_range() and madvise_free_pte_range(), folio_mapcount() is used to check whether the folio is shared. But it's not correct as folio_mapcount() returns total mapcount of large folio.

Use folio_estimated_sharers() here as the estimated number is enough.

This patchset will fix the cases: User space application call madvise() with MADV_FREE, MADV_COLD and MADV_PAGEOUT for specific address range. There are THP mapped to the range. Without the patchset, the THP is skipped. With the patch, the THP will be split and handled accordingly.

David reported the cow self test skip some cases because of MADV_PAGEOUT skip THP: https://lore.kernel.org/linux-mm/9e92e42d-488f-47db-ac9d-75b24cd0d037@intel.... and I confirmed this patchset make it work again.

This patch (of 3):

Commit 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to use folios") replaced the page_mapcount() with folio_mapcount() to check whether the folio is shared by other mapping.

It's not correct for large folio. 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/20230808020917.2230692-1-fengwei.yin@intel.com Link: https://lkml.kernel.org/r/20230808020917.2230692-2-fengwei.yin@intel.com Fixes: 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to use folios") 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 2f406263e3e954aa24c1248edcfa9be0c1bb30fa) --- mm/madvise.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c index b5ffbaf616f5..6adee363a9fa 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -375,7 +375,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, folio = pfn_folio(pmd_pfn(orig_pmd));

/* Do not interfere with other mappings of this folio */ - if (folio_mapcount(folio) != 1) + if (folio_estimated_sharers(folio) != 1) goto huge_unlock;

if (pageout_anon_only_filter && !folio_test_anon(folio)) @@ -447,7 +447,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, * are sure it's worth. Split it if we are only owner. */ if (folio_test_large(folio)) { - if (folio_mapcount(folio) != 1) + if (folio_estimated_sharers(folio) != 1) break; if (pageout_anon_only_filter && !folio_test_anon(folio)) break;