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-rw-r--r--mm/mlock.c6
-rw-r--r--mm/swap.c82
-rw-r--r--mm/vmscan.c59
3 files changed, 54 insertions, 93 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index 79398200e423..74e5a6547c3d 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -64,6 +64,12 @@ void clear_page_mlock(struct page *page)
mod_zone_page_state(page_zone(page), NR_MLOCK,
-hpage_nr_pages(page));
count_vm_event(UNEVICTABLE_PGCLEARED);
+ /*
+ * The previous TestClearPageMlocked() corresponds to the smp_mb()
+ * in __pagevec_lru_add_fn().
+ *
+ * See __pagevec_lru_add_fn for more explanation.
+ */
if (!isolate_lru_page(page)) {
putback_lru_page(page);
} else {
diff --git a/mm/swap.c b/mm/swap.c
index 567a7b96e41d..2d337710218f 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -446,30 +446,6 @@ void lru_cache_add(struct page *page)
}
/**
- * add_page_to_unevictable_list - add a page to the unevictable list
- * @page: the page to be added to the unevictable list
- *
- * Add page directly to its zone's unevictable list. To avoid races with
- * tasks that might be making the page evictable, through eg. munlock,
- * munmap or exit, while it's not on the lru, we want to add the page
- * while it's locked or otherwise "invisible" to other tasks. This is
- * difficult to do when using the pagevec cache, so bypass that.
- */
-void add_page_to_unevictable_list(struct page *page)
-{
- struct pglist_data *pgdat = page_pgdat(page);
- struct lruvec *lruvec;
-
- spin_lock_irq(&pgdat->lru_lock);
- lruvec = mem_cgroup_page_lruvec(page, pgdat);
- ClearPageActive(page);
- SetPageUnevictable(page);
- SetPageLRU(page);
- add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
- spin_unlock_irq(&pgdat->lru_lock);
-}
-
-/**
* lru_cache_add_active_or_unevictable
* @page: the page to be added to LRU
* @vma: vma in which page is mapped for determining reclaimability
@@ -484,13 +460,9 @@ void lru_cache_add_active_or_unevictable(struct page *page,
{
VM_BUG_ON_PAGE(PageLRU(page), page);
- if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED)) {
+ if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
SetPageActive(page);
- lru_cache_add(page);
- return;
- }
-
- if (!TestSetPageMlocked(page)) {
+ else if (!TestSetPageMlocked(page)) {
/*
* We use the irq-unsafe __mod_zone_page_stat because this
* counter is not modified from interrupt context, and the pte
@@ -500,7 +472,7 @@ void lru_cache_add_active_or_unevictable(struct page *page,
hpage_nr_pages(page));
count_vm_event(UNEVICTABLE_PGMLOCKED);
}
- add_page_to_unevictable_list(page);
+ lru_cache_add(page);
}
/*
@@ -886,15 +858,55 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
void *arg)
{
- int file = page_is_file_cache(page);
- int active = PageActive(page);
- enum lru_list lru = page_lru(page);
+ enum lru_list lru;
+ int was_unevictable = TestClearPageUnevictable(page);
VM_BUG_ON_PAGE(PageLRU(page), page);
SetPageLRU(page);
+ /*
+ * Page becomes evictable in two ways:
+ * 1) Within LRU lock [munlock_vma_pages() and __munlock_pagevec()].
+ * 2) Before acquiring LRU lock to put the page to correct LRU and then
+ * a) do PageLRU check with lock [check_move_unevictable_pages]
+ * b) do PageLRU check before lock [clear_page_mlock]
+ *
+ * (1) & (2a) are ok as LRU lock will serialize them. For (2b), we need
+ * following strict ordering:
+ *
+ * #0: __pagevec_lru_add_fn #1: clear_page_mlock
+ *
+ * SetPageLRU() TestClearPageMlocked()
+ * smp_mb() // explicit ordering // above provides strict
+ * // ordering
+ * PageMlocked() PageLRU()
+ *
+ *
+ * if '#1' does not observe setting of PG_lru by '#0' and fails
+ * isolation, the explicit barrier will make sure that page_evictable
+ * check will put the page in correct LRU. Without smp_mb(), SetPageLRU
+ * can be reordered after PageMlocked check and can make '#1' to fail
+ * the isolation of the page whose Mlocked bit is cleared (#0 is also
+ * looking at the same page) and the evictable page will be stranded
+ * in an unevictable LRU.
+ */
+ smp_mb();
+
+ if (page_evictable(page)) {
+ lru = page_lru(page);
+ update_page_reclaim_stat(lruvec, page_is_file_cache(page),
+ PageActive(page));
+ if (was_unevictable)
+ count_vm_event(UNEVICTABLE_PGRESCUED);
+ } else {
+ lru = LRU_UNEVICTABLE;
+ ClearPageActive(page);
+ SetPageUnevictable(page);
+ if (!was_unevictable)
+ count_vm_event(UNEVICTABLE_PGCULLED);
+ }
+
add_page_to_lru_list(page, lruvec, lru);
- update_page_reclaim_stat(lruvec, file, active);
trace_mm_lru_insertion(page, lru);
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 444749669187..bee53495a829 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -769,64 +769,7 @@ int remove_mapping(struct address_space *mapping, struct page *page)
*/
void putback_lru_page(struct page *page)
{
- bool is_unevictable;
- int was_unevictable = PageUnevictable(page);
-
- VM_BUG_ON_PAGE(PageLRU(page), page);
-
-redo:
- ClearPageUnevictable(page);
-
- if (page_evictable(page)) {
- /*
- * For evictable pages, we can use the cache.
- * In event of a race, worst case is we end up with an
- * unevictable page on [in]active list.
- * We know how to handle that.
- */
- is_unevictable = false;
- lru_cache_add(page);
- } else {
- /*
- * Put unevictable pages directly on zone's unevictable
- * list.
- */
- is_unevictable = true;
- add_page_to_unevictable_list(page);
- /*
- * When racing with an mlock or AS_UNEVICTABLE clearing
- * (page is unlocked) make sure that if the other thread
- * does not observe our setting of PG_lru and fails
- * isolation/check_move_unevictable_pages,
- * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
- * the page back to the evictable list.
- *
- * The other side is TestClearPageMlocked() or shmem_lock().
- */
- smp_mb();
- }
-
- /*
- * page's status can change while we move it among lru. If an evictable
- * page is on unevictable list, it never be freed. To avoid that,
- * check after we added it to the list, again.
- */
- if (is_unevictable && page_evictable(page)) {
- if (!isolate_lru_page(page)) {
- put_page(page);
- goto redo;
- }
- /* This means someone else dropped this page from LRU
- * So, it will be freed or putback to LRU again. There is
- * nothing to do here.
- */
- }
-
- if (was_unevictable && !is_unevictable)
- count_vm_event(UNEVICTABLE_PGRESCUED);
- else if (!was_unevictable && is_unevictable)
- count_vm_event(UNEVICTABLE_PGCULLED);
-
+ lru_cache_add(page);
put_page(page); /* drop ref from isolate */
}