memcg: cleanup mem_cgroup_move_parent()

mem_cgroup_move_parent() calls try_charge first and cancel_charge on
failure.  IMHO, charge/uncharge(especially charge) is high cost operation,
so we should avoid it as far as possible.

This patch tries to delay try_charge in mem_cgroup_move_parent() by
re-ordering checks it does.

And this patch renames mem_cgroup_move_account() to
__mem_cgroup_move_account(), changes the return value of
__mem_cgroup_move_account() from int to void, and adds a new
wrapper(mem_cgroup_move_account()), which checks whether a @pc is valid
for moving account and calls __mem_cgroup_move_account().

This patch removes the last caller of trylock_page_cgroup(), so removes
its definition too.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@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/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 4b938d4..b0e4eb1 100644 (file)
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -57,6 +57,8 @@ static inline void ClearPageCgroup##uname(struct page_cgroup *pc)     \
 static inline int TestClearPageCgroup##uname(struct page_cgroup *pc)   \
        { return test_and_clear_bit(PCG_##lname, &pc->flags);  }
 
+TESTPCGFLAG(Locked, LOCK)
+
 /* Cache flag is set only once (at allocation) */
 TESTPCGFLAG(Cache, CACHE)
 CLEARPCGFLAG(Cache, CACHE)
@@ -86,11 +88,6 @@ static inline void lock_page_cgroup(struct page_cgroup *pc)
        bit_spin_lock(PCG_LOCK, &pc->flags);
 }
 
-static inline int trylock_page_cgroup(struct page_cgroup *pc)
-{
-       return bit_spin_trylock(PCG_LOCK, &pc->flags);
-}
-
 static inline void unlock_page_cgroup(struct page_cgroup *pc)
 {
        bit_spin_unlock(PCG_LOCK, &pc->flags);

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2d6b4a9..6273984 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1613,27 +1613,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 }
 
 /**
- * mem_cgroup_move_account - move account of the page
+ * __mem_cgroup_move_account - move account of the page
  * @pc:        page_cgroup of the page.
  * @from: mem_cgroup which the page is moved from.
  * @to:        mem_cgroup which the page is moved to. @from != @to.
  *
  * The caller must confirm following.
  * - page is not on LRU (isolate_page() is useful.)
- *
- * returns 0 at success,
- * returns -EBUSY when lock is busy or "pc" is unstable.
+ * - the pc is locked, used, and ->mem_cgroup points to @from.
  *
  * This function does "uncharge" from old cgroup but doesn't do "charge" to
  * new cgroup. It should be done by a caller.
  */
 
-static int mem_cgroup_move_account(struct page_cgroup *pc,
+static void __mem_cgroup_move_account(struct page_cgroup *pc,
        struct mem_cgroup *from, struct mem_cgroup *to)
 {
-       struct mem_cgroup_per_zone *from_mz, *to_mz;
-       int nid, zid;
-       int ret = -EBUSY;
        struct page *page;
        int cpu;
        struct mem_cgroup_stat *stat;
@@ -1641,20 +1636,9 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 
        VM_BUG_ON(from == to);
        VM_BUG_ON(PageLRU(pc->page));
-
-       nid = page_cgroup_nid(pc);
-       zid = page_cgroup_zid(pc);
-       from_mz =  mem_cgroup_zoneinfo(from, nid, zid);
-       to_mz =  mem_cgroup_zoneinfo(to, nid, zid);
-
-       if (!trylock_page_cgroup(pc))
-               return ret;
-
-       if (!PageCgroupUsed(pc))
-               goto out;
-
-       if (pc->mem_cgroup != from)
-               goto out;
+       VM_BUG_ON(!PageCgroupLocked(pc));
+       VM_BUG_ON(!PageCgroupUsed(pc));
+       VM_BUG_ON(pc->mem_cgroup != from);
 
        if (!mem_cgroup_is_root(from))
                res_counter_uncharge(&from->res, PAGE_SIZE);
@@ -1683,15 +1667,28 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
        css_get(&to->css);
        pc->mem_cgroup = to;
        mem_cgroup_charge_statistics(to, pc, true);
-       ret = 0;
-out:
-       unlock_page_cgroup(pc);
        /*
         * We charges against "to" which may not have any tasks. Then, "to"
         * can be under rmdir(). But in current implementation, caller of
         * this function is just force_empty() and it's garanteed that
         * "to" is never removed. So, we don't check rmdir status here.
         */
+}
+
+/*
+ * check whether the @pc is valid for moving account and call
+ * __mem_cgroup_move_account()
+ */
+static int mem_cgroup_move_account(struct page_cgroup *pc,
+                               struct mem_cgroup *from, struct mem_cgroup *to)
+{
+       int ret = -EINVAL;
+       lock_page_cgroup(pc);
+       if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
+               __mem_cgroup_move_account(pc, from, to);
+               ret = 0;
+       }
+       unlock_page_cgroup(pc);
        return ret;
 }
 
@@ -1713,38 +1710,27 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
        if (!pcg)
                return -EINVAL;
 
+       ret = -EBUSY;
+       if (!get_page_unless_zero(page))
+               goto out;
+       if (isolate_lru_page(page))
+               goto put;
 
        parent = mem_cgroup_from_cont(pcg);
-
-
        ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, page);
        if (ret || !parent)
-               return ret;
-
-       if (!get_page_unless_zero(page)) {
-               ret = -EBUSY;
-               goto uncharge;
-       }
-
-       ret = isolate_lru_page(page);
-
-       if (ret)
-               goto cancel;
+               goto put_back;
 
        ret = mem_cgroup_move_account(pc, child, parent);
-
+       if (!ret)
+               css_put(&parent->css);  /* drop extra refcnt by try_charge() */
+       else
+               mem_cgroup_cancel_charge(parent);       /* does css_put */
+put_back:
        putback_lru_page(page);
-       if (!ret) {
-               put_page(page);
-               /* drop extra refcnt by try_charge() */
-               css_put(&parent->css);
-               return 0;
-       }
-
-cancel:
+put:
        put_page(page);
-uncharge:
-       mem_cgroup_cancel_charge(parent);
+out:
        return ret;
 }