diff --git a/mm/memory.c b/mm/memory.c index f745f5e28f0c..5d5a2d81f05a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3727,19 +3727,86 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf, struct folio *folio) return ret; } -static bool wp_can_reuse_anon_folio(struct folio *folio, - struct vm_area_struct *vma) +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +static bool __wp_can_reuse_large_anon_folio(struct folio *folio, + struct vm_area_struct *vma) { + bool exclusive = false; + + /* Let's just free up a large folio if only a single page is mapped. */ + if (folio_large_mapcount(folio) <= 1) + return false; + /* - * We could currently only reuse a subpage of a large folio if no - * other subpages of the large folios are still mapped. However, - * let's just consistently not reuse subpages even if we could - * reuse in that scenario, and give back a large folio a bit - * sooner. + * The assumption for anonymous folios is that each page can only get + * mapped once into each MM. The only exception are KSM folios, which + * are always small. + * + * Each taken mapcount must be paired with exactly one taken reference, + * whereby the refcount must be incremented before the mapcount when + * mapping a page, and the refcount must be decremented after the + * mapcount when unmapping a page. + * + * If all folio references are from mappings, and all mappings are in + * the page tables of this MM, then this folio is exclusive to this MM. */ - if (folio_test_large(folio)) + if (folio_test_large_maybe_mapped_shared(folio)) + return false; + + VM_WARN_ON_ONCE(folio_test_ksm(folio)); + VM_WARN_ON_ONCE(folio_mapcount(folio) > folio_nr_pages(folio)); + VM_WARN_ON_ONCE(folio_entire_mapcount(folio)); + + if (unlikely(folio_test_swapcache(folio))) { + /* + * Note: freeing up the swapcache will fail if some PTEs are + * still swap entries. + */ + if (!folio_trylock(folio)) + return false; + folio_free_swap(folio); + folio_unlock(folio); + } + + if (folio_large_mapcount(folio) != folio_ref_count(folio)) return false; + /* Stabilize the mapcount vs. refcount and recheck. */ + folio_lock_large_mapcount(folio); + VM_WARN_ON_ONCE(folio_large_mapcount(folio) < folio_ref_count(folio)); + + if (folio_test_large_maybe_mapped_shared(folio)) + goto unlock; + if (folio_large_mapcount(folio) != folio_ref_count(folio)) + goto unlock; + + VM_WARN_ON_ONCE(folio_mm_id(folio, 0) != vma->vm_mm->mm_id && + folio_mm_id(folio, 1) != vma->vm_mm->mm_id); + + /* + * Do we need the folio lock? Likely not. If there would have been + * references from page migration/swapout, we would have detected + * an additional folio reference and never ended up here. + */ + exclusive = true; +unlock: + folio_unlock_large_mapcount(folio); + return exclusive; +} +#else /* !CONFIG_TRANSPARENT_HUGEPAGE */ +static bool __wp_can_reuse_large_anon_folio(struct folio *folio, + struct vm_area_struct *vma) +{ + BUILD_BUG(); +} +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ + +static bool wp_can_reuse_anon_folio(struct folio *folio, + struct vm_area_struct *vma) +{ + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && folio_test_large(folio)) + return __wp_can_reuse_large_anon_folio(folio, vma); + /* * We have to verify under folio lock: these early checks are * just an optimization to avoid locking the folio and freeing