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Commit 9476db97 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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mm: memcontrol: simplify move precharge function 



The move precharge function does some baroque things: it tries raw
res_counter charging of the entire amount first, and then falls back to
a loop of one-by-one charges, with checks for pending signals and
cond_resched() batching.

Just use mem_cgroup_try_charge() without __GFP_WAIT for the first bulk
charge attempt.  In the one-by-one loop, remove the signal check (this
is already checked in try_charge), and simply call cond_resched() after
every charge - it's not that expensive.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0029e19e

mm/memcontrol.c

+15 −33
Original line number Diff line number Diff line
@@ -6385,56 +6385,38 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css) 


#ifdef CONFIG_MMU

/* Handlers for move charge at task migration. */

#define PRECHARGE_COUNT_AT_ONCE	256

static int mem_cgroup_do_precharge(unsigned long count)

{

	int ret = 0;

	int batch_count = PRECHARGE_COUNT_AT_ONCE;

	struct mem_cgroup *memcg = mc.to;



	if (mem_cgroup_is_root(memcg)) {

	if (mem_cgroup_is_root(mc.to)) {

		mc.precharge += count;

		/* we don't need css_get for root */

		return ret;

	}

	/* try to charge at once */

	if (count > 1) {

		struct res_counter *dummy;

		/*

		 * "memcg" cannot be under rmdir() because we've already checked

		 * by cgroup_lock_live_cgroup() that it is not removed and we

		 * are still under the same cgroup_mutex. So we can postpone

		 * css_get().

		 */

		if (res_counter_charge(&memcg->res, PAGE_SIZE * count, &dummy))

			goto one_by_one;

		if (do_swap_account && res_counter_charge(&memcg->memsw,

						PAGE_SIZE * count, &dummy)) {

			res_counter_uncharge(&memcg->res, PAGE_SIZE * count);

			goto one_by_one;

		}



	/* Try a single bulk charge without reclaim first */

	ret = mem_cgroup_try_charge(mc.to, GFP_KERNEL & ~__GFP_WAIT, count);

	if (!ret) {

		mc.precharge += count;

		return ret;

	}

one_by_one:

	/* fall back to one by one charge */



	/* Try charges one by one with reclaim */

	while (count--) {

		if (signal_pending(current)) {

			ret = -EINTR;

			break;

		}

		if (!batch_count--) {

			batch_count = PRECHARGE_COUNT_AT_ONCE;

			cond_resched();

		}

		ret = mem_cgroup_try_charge(memcg,

		ret = mem_cgroup_try_charge(mc.to,

					    GFP_KERNEL & ~__GFP_NORETRY, 1);

		/*

		 * In case of failure, any residual charges against

		 * mc.to will be dropped by mem_cgroup_clear_mc()

		 * later on.

		 */

		if (ret)

			/* mem_cgroup_clear_mc() will do uncharge later */

			return ret;

		mc.precharge++;

		cond_resched();

	}

	return ret;

	return 0;

}



/**