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madvise:madvise_free_pte_range(): don't use mapcount() against large folio for sharing check
commit0e0e9bd5f7
upstream. Commit98b211d641
("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:98b211d641
("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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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2 changed files with 21 additions and 2 deletions
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@ -1727,6 +1727,25 @@ static inline size_t folio_size(struct folio *folio)
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return PAGE_SIZE << folio_order(folio);
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return PAGE_SIZE << folio_order(folio);
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}
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}
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/**
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* folio_estimated_sharers - Estimate the number of sharers of a folio.
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* @folio: The folio.
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*
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* folio_estimated_sharers() aims to serve as a function to efficiently
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* estimate the number of processes sharing a folio. This is done by
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* looking at the precise mapcount of the first subpage in the folio, and
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* assuming the other subpages are the same. This may not be true for large
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* folios. If you want exact mapcounts for exact calculations, look at
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* page_mapcount() or folio_total_mapcount().
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*
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* Return: The estimated number of processes sharing a folio.
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*/
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static inline int folio_estimated_sharers(struct folio *folio)
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{
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return page_mapcount(folio_page(folio, 0));
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}
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#ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
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#ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
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static inline int arch_make_page_accessible(struct page *page)
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static inline int arch_make_page_accessible(struct page *page)
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{
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{
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@ -654,8 +654,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
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* deactivate all pages.
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* deactivate all pages.
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*/
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*/
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if (folio_test_large(folio)) {
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if (folio_test_large(folio)) {
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if (folio_mapcount(folio) != 1)
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if (folio_estimated_sharers(folio) != 1)
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goto out;
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break;
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folio_get(folio);
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folio_get(folio);
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if (!folio_trylock(folio)) {
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if (!folio_trylock(folio)) {
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folio_put(folio);
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folio_put(folio);
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