diff options
Diffstat (limited to 'mm/rmap.c')
| -rw-r--r-- | mm/rmap.c | 65 |
1 files changed, 45 insertions, 20 deletions
diff --git a/mm/rmap.c b/mm/rmap.c index 0c7b2a9400d4..b3e381919835 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -251,18 +251,37 @@ static inline void unlock_anon_vma_root(struct anon_vma *root) * Attach the anon_vmas from src to dst. * Returns 0 on success, -ENOMEM on failure. * - * If dst->anon_vma is NULL this function tries to find and reuse existing - * anon_vma which has no vmas and only one child anon_vma. This prevents - * degradation of anon_vma hierarchy to endless linear chain in case of - * constantly forking task. On the other hand, an anon_vma with more than one - * child isn't reused even if there was no alive vma, thus rmap walker has a - * good chance of avoiding scanning the whole hierarchy when it searches where - * page is mapped. + * anon_vma_clone() is called by __vma_split(), __split_vma(), copy_vma() and + * anon_vma_fork(). The first three want an exact copy of src, while the last + * one, anon_vma_fork(), may try to reuse an existing anon_vma to prevent + * endless growth of anon_vma. Since dst->anon_vma is set to NULL before call, + * we can identify this case by checking (!dst->anon_vma && src->anon_vma). + * + * If (!dst->anon_vma && src->anon_vma) is true, this function tries to find + * and reuse existing anon_vma which has no vmas and only one child anon_vma. + * This prevents degradation of anon_vma hierarchy to endless linear chain in + * case of constantly forking task. On the other hand, an anon_vma with more + * than one child isn't reused even if there was no alive vma, thus rmap + * walker has a good chance of avoiding scanning the whole hierarchy when it + * searches where page is mapped. */ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) { struct anon_vma_chain *avc, *pavc; struct anon_vma *root = NULL; + struct vm_area_struct *prev = dst->vm_prev, *pprev = src->vm_prev; + + /* + * If parent share anon_vma with its vm_prev, keep this sharing in in + * child. + * + * 1. Parent has vm_prev, which implies we have vm_prev. + * 2. Parent and its vm_prev have the same anon_vma. + */ + if (!dst->anon_vma && src->anon_vma && + pprev && pprev->anon_vma == src->anon_vma) + dst->anon_vma = prev->anon_vma; + list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) { struct anon_vma *anon_vma; @@ -287,8 +306,8 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) * will always reuse it. Root anon_vma is never reused: * it has self-parent reference and at least one child. */ - if (!dst->anon_vma && anon_vma != src->anon_vma && - anon_vma->degree < 2) + if (!dst->anon_vma && src->anon_vma && + anon_vma != src->anon_vma && anon_vma->degree < 2) dst->anon_vma = anon_vma; } if (dst->anon_vma) @@ -458,9 +477,10 @@ void __init anon_vma_init(void) * chain and verify that the page in question is indeed mapped in it * [ something equivalent to page_mapped_in_vma() ]. * - * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap() - * that the anon_vma pointer from page->mapping is valid if there is a - * mapcount, we can dereference the anon_vma after observing those. + * Since anon_vma's slab is SLAB_TYPESAFE_BY_RCU and we know from + * page_remove_rmap() that the anon_vma pointer from page->mapping is valid + * if there is a mapcount, we can dereference the anon_vma after observing + * those. */ struct anon_vma *page_get_anon_vma(struct page *page) { @@ -1055,7 +1075,6 @@ static void __page_set_anon_rmap(struct page *page, static void __page_check_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { -#ifdef CONFIG_DEBUG_VM /* * The page's anon-rmap details (mapping and index) are guaranteed to * be set up correctly at this point. @@ -1068,9 +1087,9 @@ static void __page_check_anon_rmap(struct page *page, * are initially only visible via the pagetables, and the pte is locked * over the call to page_add_new_anon_rmap. */ - BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root); - BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address)); -#endif + VM_BUG_ON_PAGE(page_anon_vma(page)->root != vma->anon_vma->root, page); + VM_BUG_ON_PAGE(page_to_pgoff(page) != linear_page_index(vma, address), + page); } /** @@ -1273,12 +1292,20 @@ static void page_remove_anon_compound_rmap(struct page *page) if (TestClearPageDoubleMap(page)) { /* * Subpages can be mapped with PTEs too. Check how many of - * themi are still mapped. + * them are still mapped. */ for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) { if (atomic_add_negative(-1, &page[i]._mapcount)) nr++; } + + /* + * Queue the page for deferred split if at least one small + * page of the compound page is unmapped, but at least one + * small page is still mapped. + */ + if (nr && nr < HPAGE_PMD_NR) + deferred_split_huge_page(page); } else { nr = HPAGE_PMD_NR; } @@ -1286,10 +1313,8 @@ static void page_remove_anon_compound_rmap(struct page *page) if (unlikely(PageMlocked(page))) clear_page_mlock(page); - if (nr) { + if (nr) __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr); - deferred_split_huge_page(page); - } } /** |