memcg: fix LRU accounting for SwapCache

Now, a page can be deleted from SwapCache while do_swap_page().
memcg-fix-swap-accounting-leak-v3.patch handles that, but, LRU handling is
still broken.  (above behavior broke assumption of memcg-synchronized-lru
patch.)

This patch is a fix for LRU handling (especially for per-zone counters).
At charging SwapCache,
 - Remove page_cgroup from LRU if it's not used.
 - Add page cgroup to LRU if it's not linked to.

Reported-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b311f19bbe01102445179b5ec8d227e0cfcd8d9f..f50cb7b1efdb66aa9e03e6a2bf53e02ecc81241d 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -331,8 +331,12 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
                return;
        pc = lookup_page_cgroup(page);
        /* can happen while we handle swapcache. */
-       if (list_empty(&pc->lru))
+       if (list_empty(&pc->lru) || !pc->mem_cgroup)
                return;
+       /*
+        * We don't check PCG_USED bit. It's cleared when the "page" is finally
+        * removed from global LRU.
+        */
        mz = page_cgroup_zoneinfo(pc);
        mem = pc->mem_cgroup;
        MEM_CGROUP_ZSTAT(mz, lru) -= 1;
@@ -379,16 +383,44 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
        MEM_CGROUP_ZSTAT(mz, lru) += 1;
        list_add(&pc->lru, &mz->lists[lru]);
 }
+
 /*
- * To add swapcache into LRU. Be careful to all this function.
- * zone->lru_lock shouldn't be held and irq must not be disabled.
+ * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
+ * lru because the page may.be reused after it's fully uncharged (because of
+ * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
+ * it again. This function is only used to charge SwapCache. It's done under
+ * lock_page and expected that zone->lru_lock is never held.
  */
-static void mem_cgroup_lru_fixup(struct page *page)
+static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
+{
+       unsigned long flags;
+       struct zone *zone = page_zone(page);
+       struct page_cgroup *pc = lookup_page_cgroup(page);
+
+       spin_lock_irqsave(&zone->lru_lock, flags);
+       /*
+        * Forget old LRU when this page_cgroup is *not* used. This Used bit
+        * is guarded by lock_page() because the page is SwapCache.
+        */
+       if (!PageCgroupUsed(pc))
+               mem_cgroup_del_lru_list(page, page_lru(page));
+       spin_unlock_irqrestore(&zone->lru_lock, flags);
+}
+
+static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
 {
-       if (!isolate_lru_page(page))
-               putback_lru_page(page);
+       unsigned long flags;
+       struct zone *zone = page_zone(page);
+       struct page_cgroup *pc = lookup_page_cgroup(page);
+
+       spin_lock_irqsave(&zone->lru_lock, flags);
+       /* link when the page is linked to LRU but page_cgroup isn't */
+       if (PageLRU(page) && list_empty(&pc->lru))
+               mem_cgroup_add_lru_list(page, page_lru(page));
+       spin_unlock_irqrestore(&zone->lru_lock, flags);
 }
 
+
 void mem_cgroup_move_lists(struct page *page,
                           enum lru_list from, enum lru_list to)
 {
@@ -1168,8 +1200,11 @@ int mem_cgroup_cache_charge_swapin(struct page *page,
                                        mem = NULL; /* charge to current */
                        }
                }
+               /* SwapCache may be still linked to LRU now. */
+               mem_cgroup_lru_del_before_commit_swapcache(page);
                ret = mem_cgroup_charge_common(page, mm, mask,
                                MEM_CGROUP_CHARGE_TYPE_SHMEM, mem);
+               mem_cgroup_lru_add_after_commit_swapcache(page);
                /* drop extra refcnt from tryget */
                if (mem)
                        css_put(&mem->css);
@@ -1185,8 +1220,6 @@ int mem_cgroup_cache_charge_swapin(struct page *page,
        }
        if (!locked)
                unlock_page(page);
-       /* add this page(page_cgroup) to the LRU we want. */
-       mem_cgroup_lru_fixup(page);
 
        return ret;
 }
@@ -1201,7 +1234,9 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
        if (!ptr)
                return;
        pc = lookup_page_cgroup(page);
+       mem_cgroup_lru_del_before_commit_swapcache(page);
        __mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
+       mem_cgroup_lru_add_after_commit_swapcache(page);
        /*
         * Now swap is on-memory. This means this page may be
         * counted both as mem and swap....double count.
@@ -1220,7 +1255,7 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
 
        }
        /* add this page(page_cgroup) to the LRU we want. */
-       mem_cgroup_lru_fixup(page);
+
 }
 
 void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
@@ -1288,6 +1323,12 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
        mem_cgroup_charge_statistics(mem, pc, false);
        ClearPageCgroupUsed(pc);
+       /*
+        * pc->mem_cgroup is not cleared here. It will be accessed when it's
+        * freed from LRU. This is safe because uncharged page is expected not
+        * to be reused (freed soon). Exception is SwapCache, it's handled by
+        * special functions.
+        */
 
        mz = page_cgroup_zoneinfo(pc);
        unlock_page_cgroup(pc);