Commit 98b211d6415f ("madvise: convert madvise_free_pte_range() 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/20230808020917.2230692-4-fengwei.yin@intel.com Fixes: 98b211d6415f ("madvise: convert madvise_free_pte_range() 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 0e0e9bd5f7b9d40fd03b70092367247d52da1db0) --- mm/madvise.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/madvise.c b/mm/madvise.c index b5ffbaf616f5..584ff190bf90 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -664,8 +664,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, * deactivate all pages. */ if (folio_test_large(folio)) { - if (folio_mapcount(folio) != 1) - goto out; + if (folio_estimated_sharers(folio) != 1) + break; folio_get(folio); if (!folio_trylock(folio)) { folio_put(folio);