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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id v9sm84364pfn.22.2021.06.03.15.32.11 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Thu, 03 Jun 2021 15:32:12 -0700 (PDT) Date: Thu, 3 Jun 2021 15:32:10 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Hugh Dickins , "Kirill A. Shutemov" , Yang Shi , Wang Yugui , Matthew Wilcox , Naoya Horiguchi , Alistair Popple , Ralph Campbell , Zi Yan , Miaohe Lin , Minchan Kim , Jue Wang , Peter Xu , Jan Kara , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.2/7] mm: rmap: make try_to_unmap() void function Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=JjGzfKQz; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.215.177 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: uoxdhckhkh6yf1yxwn8bko1c6gd3q4ee X-Rspamd-Queue-Id: 898D3801973B X-Rspamd-Server: rspam02 X-HE-Tag: 1622759540-254149 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Yang Shi Currently try_to_unmap() return bool value by checking page_mapcount(), however this may return false positive since page_mapcount() doesn't check all subpages of compound page. The total_mapcount() could be used instead, but its cost is higher since it traverses all subpages. Actually the most callers of try_to_unmap() don't care about the return value at all. So just need check if page is still mapped by page_mapped() when necessary. And page_mapped() does bail out early when it finds mapped subpage. Suggested-by: Hugh Dickins Signed-off-by: Yang Shi Acked-by: Minchan Kim Reviewed-by: Shakeel Butt Acked-by: Kirill A. Shutemov Signed-off-by: Hugh Dickins --- v5: Rediffed by Hugh to fit before 7/7 in mm/thp series; akpm fixed grammar. v4: Updated the comment of try_to_unmap() per Minchan. Minor fix and patch reorder per Hugh. Collected ack tag from Hugh. include/linux/rmap.h | 2 +- mm/memory-failure.c | 15 +++++++-------- mm/rmap.c | 15 ++++----------- mm/vmscan.c | 3 ++- 4 files changed, 14 insertions(+), 21 deletions(-) --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -195,7 +195,7 @@ static inline void page_dup_rmap(struct int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg, unsigned long *vm_flags); -bool try_to_unmap(struct page *, enum ttu_flags flags); +void try_to_unmap(struct page *, enum ttu_flags flags); /* Avoid racy checks */ #define PVMW_SYNC (1 << 0) --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1063,7 +1063,7 @@ static bool hwpoison_user_mappings(struc enum ttu_flags ttu = TTU_IGNORE_MLOCK; struct address_space *mapping; LIST_HEAD(tokill); - bool unmap_success = true; + bool unmap_success; int kill = 1, forcekill; struct page *hpage = *hpagep; bool mlocked = PageMlocked(hpage); @@ -1126,7 +1126,7 @@ static bool hwpoison_user_mappings(struc collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED); if (!PageHuge(hpage)) { - unmap_success = try_to_unmap(hpage, ttu); + try_to_unmap(hpage, ttu); } else { if (!PageAnon(hpage)) { /* @@ -1138,17 +1138,16 @@ static bool hwpoison_user_mappings(struc */ mapping = hugetlb_page_mapping_lock_write(hpage); if (mapping) { - unmap_success = try_to_unmap(hpage, - ttu|TTU_RMAP_LOCKED); + try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED); i_mmap_unlock_write(mapping); - } else { + } else pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn); - unmap_success = false; - } } else { - unmap_success = try_to_unmap(hpage, ttu); + try_to_unmap(hpage, ttu); } } + + unmap_success = !page_mapped(hpage); if (!unmap_success) pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n", pfn, page_mapcount(hpage)); --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1405,7 +1405,7 @@ static bool try_to_unmap_one(struct page /* * When racing against e.g. zap_pte_range() on another cpu, * in between its ptep_get_and_clear_full() and page_remove_rmap(), - * try_to_unmap() may return false when it is about to become true, + * try_to_unmap() may return before page_mapped() has become false, * if page table locking is skipped: use TTU_SYNC to wait for that. */ if (flags & TTU_SYNC) @@ -1756,9 +1756,10 @@ static int page_not_mapped(struct page * * Tries to remove all the page table entries which are mapping this * page, used in the pageout path. Caller must hold the page lock. * - * If unmap is successful, return true. Otherwise, false. + * It is the caller's responsibility to check if the page is still + * mapped when needed (use TTU_SYNC to prevent accounting races). */ -bool try_to_unmap(struct page *page, enum ttu_flags flags) +void try_to_unmap(struct page *page, enum ttu_flags flags) { struct rmap_walk_control rwc = { .rmap_one = try_to_unmap_one, @@ -1783,14 +1784,6 @@ bool try_to_unmap(struct page *page, enu rmap_walk_locked(page, &rwc); else rmap_walk(page, &rwc); - - /* - * When racing against e.g. zap_pte_range() on another cpu, - * in between its ptep_get_and_clear_full() and page_remove_rmap(), - * try_to_unmap() may return false when it is about to become true, - * if page table locking is skipped: use TTU_SYNC to wait for that. - */ - return !page_mapcount(page); } /** --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(str if (unlikely(PageTransHuge(page))) flags |= TTU_SPLIT_HUGE_PMD; - if (!try_to_unmap(page, flags)) { + try_to_unmap(page, flags); + if (page_mapped(page)) { stat->nr_unmap_fail += nr_pages; if (!was_swapbacked && PageSwapBacked(page)) stat->nr_lazyfree_fail += nr_pages;