From 09854ba94c6aad7886996bfbee2530b3d8a7f4f4 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 21 Aug 2020 19:49:55 -0400 Subject: mm: do_wp_page() simplification How about we just make sure we're the only possible valid user fo the page before we bother to reuse it? Simplify, simplify, simplify. And get rid of the nasty serialization on the page lock at the same time. [peterx: add subject prefix] Signed-off-by: Linus Torvalds Signed-off-by: Peter Xu Signed-off-by: Linus Torvalds --- mm/memory.c | 59 +++++++++++++++++------------------------------------------ 1 file changed, 17 insertions(+), 42 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index 3ecad55103ad..56ae945c6845 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2924,50 +2924,25 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) * not dirty accountable. */ if (PageAnon(vmf->page)) { - int total_map_swapcount; - if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) || - page_count(vmf->page) != 1)) + struct page *page = vmf->page; + + /* PageKsm() doesn't necessarily raise the page refcount */ + if (PageKsm(page) || page_count(page) != 1) + goto copy; + if (!trylock_page(page)) + goto copy; + if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) { + unlock_page(page); goto copy; - if (!trylock_page(vmf->page)) { - get_page(vmf->page); - pte_unmap_unlock(vmf->pte, vmf->ptl); - lock_page(vmf->page); - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, - vmf->address, &vmf->ptl); - if (!pte_same(*vmf->pte, vmf->orig_pte)) { - update_mmu_tlb(vma, vmf->address, vmf->pte); - unlock_page(vmf->page); - pte_unmap_unlock(vmf->pte, vmf->ptl); - put_page(vmf->page); - return 0; - } - put_page(vmf->page); - } - if (PageKsm(vmf->page)) { - bool reused = reuse_ksm_page(vmf->page, vmf->vma, - vmf->address); - unlock_page(vmf->page); - if (!reused) - goto copy; - wp_page_reuse(vmf); - return VM_FAULT_WRITE; - } - if (reuse_swap_page(vmf->page, &total_map_swapcount)) { - if (total_map_swapcount == 1) { - /* - * The page is all ours. Move it to - * our anon_vma so the rmap code will - * not search our parent or siblings. - * Protected against the rmap code by - * the page lock. - */ - page_move_anon_rmap(vmf->page, vma); - } - unlock_page(vmf->page); - wp_page_reuse(vmf); - return VM_FAULT_WRITE; } - unlock_page(vmf->page); + /* + * Ok, we've got the only map reference, and the only + * page count reference, and the page is locked, + * it's dark out, and we're wearing sunglasses. Hit it. + */ + wp_page_reuse(vmf); + unlock_page(page); + return VM_FAULT_WRITE; } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED))) { return wp_page_shared(vmf); -- cgit v1.2.3 From 798a6b87ecd72828a6c6b5469aaa2032a57e92b7 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Fri, 21 Aug 2020 19:49:58 -0400 Subject: mm: Add PGREUSE counter This accounts for wp_page_reuse() case, where we reused a page for COW. Signed-off-by: Peter Xu Signed-off-by: Linus Torvalds --- include/linux/vm_event_item.h | 1 + mm/memory.c | 1 + mm/vmstat.c | 1 + 3 files changed, 3 insertions(+) (limited to 'mm/memory.c') diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 24fc7c3ae7d6..58d3f91baad1 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -30,6 +30,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, PGFAULT, PGMAJFAULT, PGLAZYFREED, PGREFILL, + PGREUSE, PGSTEAL_KSWAPD, PGSTEAL_DIRECT, PGSCAN_KSWAPD, diff --git a/mm/memory.c b/mm/memory.c index 56ae945c6845..20d93001ef93 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2619,6 +2619,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf) if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1)) update_mmu_cache(vma, vmf->address, vmf->pte); pte_unmap_unlock(vmf->pte, vmf->ptl); + count_vm_event(PGREUSE); } /* diff --git a/mm/vmstat.c b/mm/vmstat.c index 3fb23a21f6dd..907a5045bfa3 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1198,6 +1198,7 @@ const char * const vmstat_text[] = { "pglazyfreed", "pgrefill", + "pgreuse", "pgsteal_kswapd", "pgsteal_direct", "pgscan_kswapd", -- cgit v1.2.3