bugfix for memory controller: add helper function for assigning cgroup to page

This patch adds following functions.
   - clear_page_cgroup(page, pc)
   - page_cgroup_assign_new_page_group(page, pc)

Mainly for cleanup.

A manner "check page->cgroup again after lock_page_cgroup()" is
implemented in straight way.

A comment in mem_cgroup_uncharge() will be removed by force-empty patch

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.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 2fadd48..3270ce7 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -162,6 +162,48 @@ static void __always_inline unlock_page_cgroup(struct page *page)
        bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
 }
 
+/*
+ * Tie new page_cgroup to struct page under lock_page_cgroup()
+ * This can fail if the page has been tied to a page_cgroup.
+ * If success, returns 0.
+ */
+static inline int
+page_cgroup_assign_new_page_cgroup(struct page *page, struct page_cgroup *pc)
+{
+       int ret = 0;
+
+       lock_page_cgroup(page);
+       if (!page_get_page_cgroup(page))
+               page_assign_page_cgroup(page, pc);
+       else /* A page is tied to other pc. */
+               ret = 1;
+       unlock_page_cgroup(page);
+       return ret;
+}
+
+/*
+ * Clear page->page_cgroup member under lock_page_cgroup().
+ * If given "pc" value is different from one page->page_cgroup,
+ * page->cgroup is not cleared.
+ * Returns a value of page->page_cgroup at lock taken.
+ * A can can detect failure of clearing by following
+ *  clear_page_cgroup(page, pc) == pc
+ */
+
+static inline struct page_cgroup *
+clear_page_cgroup(struct page *page, struct page_cgroup *pc)
+{
+       struct page_cgroup *ret;
+       /* lock and clear */
+       lock_page_cgroup(page);
+       ret = page_get_page_cgroup(page);
+       if (likely(ret == pc))
+               page_assign_page_cgroup(page, NULL);
+       unlock_page_cgroup(page);
+       return ret;
+}
+
+
 static void __mem_cgroup_move_lists(struct page_cgroup *pc, bool active)
 {
        if (active)
@@ -270,7 +312,7 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
 {
        struct mem_cgroup *mem;
-       struct page_cgroup *pc, *race_pc;
+       struct page_cgroup *pc;
        unsigned long flags;
        unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 
@@ -293,8 +335,10 @@ retry:
                        unlock_page_cgroup(page);
                        cpu_relax();
                        goto retry;
-               } else
+               } else {
+                       unlock_page_cgroup(page);
                        goto done;
+               }
        }
 
        unlock_page_cgroup(page);
@@ -364,31 +408,26 @@ noreclaim:
                goto free_pc;
        }
 
-       lock_page_cgroup(page);
-       /*
-        * Check if somebody else beat us to allocating the page_cgroup
-        */
-       race_pc = page_get_page_cgroup(page);
-       if (race_pc) {
-               kfree(pc);
-               pc = race_pc;
-               atomic_inc(&pc->ref_cnt);
-               res_counter_uncharge(&mem->res, PAGE_SIZE);
-               css_put(&mem->css);
-               goto done;
-       }
-
        atomic_set(&pc->ref_cnt, 1);
        pc->mem_cgroup = mem;
        pc->page = page;
-       page_assign_page_cgroup(page, pc);
+       if (page_cgroup_assign_new_page_cgroup(page, pc)) {
+               /*
+                * an another charge is added to this page already.
+                * we do take lock_page_cgroup(page) again and read
+                * page->cgroup, increment refcnt.... just retry is OK.
+                */
+               res_counter_uncharge(&mem->res, PAGE_SIZE);
+               css_put(&mem->css);
+               kfree(pc);
+               goto retry;
+       }
 
        spin_lock_irqsave(&mem->lru_lock, flags);
        list_add(&pc->lru, &mem->active_list);
        spin_unlock_irqrestore(&mem->lru_lock, flags);
 
 done:
-       unlock_page_cgroup(page);
        return 0;
 free_pc:
        kfree(pc);
@@ -432,17 +471,25 @@ void mem_cgroup_uncharge(struct page_cgroup *pc)
 
        if (atomic_dec_and_test(&pc->ref_cnt)) {
                page = pc->page;
-               lock_page_cgroup(page);
-               mem = pc->mem_cgroup;
-               css_put(&mem->css);
-               page_assign_page_cgroup(page, NULL);
-               unlock_page_cgroup(page);
-               res_counter_uncharge(&mem->res, PAGE_SIZE);
-
-               spin_lock_irqsave(&mem->lru_lock, flags);
-               list_del_init(&pc->lru);
-               spin_unlock_irqrestore(&mem->lru_lock, flags);
-               kfree(pc);
+               /*
+                * get page->cgroup and clear it under lock.
+                */
+               if (clear_page_cgroup(page, pc) == pc) {
+                       mem = pc->mem_cgroup;
+                       css_put(&mem->css);
+                       res_counter_uncharge(&mem->res, PAGE_SIZE);
+                       spin_lock_irqsave(&mem->lru_lock, flags);
+                       list_del_init(&pc->lru);
+                       spin_unlock_irqrestore(&mem->lru_lock, flags);
+                       kfree(pc);
+               } else {
+                       /*
+                        * Note:This will be removed when force-empty patch is
+                        * applied. just show warning here.
+                        */
+                       printk(KERN_ERR "Race in mem_cgroup_uncharge() ?");
+                       dump_stack();
+               }
        }
 }