Commit 57f9fd7d authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
Browse files

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: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a3032a2c

include/linux/page_cgroup.h

+2 −5
Original line number Diff line number Diff line
@@ -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);

mm/memcontrol.c

+35 −49
Original line number Diff line number Diff line
@@ -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:

	put_page(page);

		/* drop extra refcnt by try_charge() */

		css_put(&parent->css);

		return 0;

	}



cancel:

	put_page(page);

uncharge:

	mem_cgroup_cancel_charge(parent);

out:

	return ret;

}

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