mm: rmap: make try_to_unmap() void function

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.

Link: https://lkml.kernel.org/r/bb27e3fe-6036-b637-5086-272befbfe3da@google.com
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 8d04e7d..ed31a55 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -195,7 +195,7 @@ static inline void page_dup_rmap(struct page *page, bool compound)
 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)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 9d2d31f..419d92b 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1269,7 +1269,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
        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);
@@ -1332,7 +1332,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
                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)) {
                        /*
@@ -1344,17 +1344,16 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
                         */
                        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));

diff --git a/mm/rmap.c b/mm/rmap.c
index e05c300..f9fd5bc 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1405,7 +1405,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
        /*
         * 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 *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, enum ttu_flags flags)
                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);
 }
 
 /**

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7b52ab1..e1d75e6 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(struct list_head *page_list,
                        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;