Commit b6b6cc72 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

memcg: do not replicate get_mem_cgroup_from_mm in __mem_cgroup_try_charge 



__mem_cgroup_try_charge duplicates get_mem_cgroup_from_mm for charges
which came without a memcg.  The only reason seems to be a tiny
optimization when css_tryget is not called if the charge can be consumed
from the stock.  Nevertheless css_tryget is very cheap since it has been
reworked to use per-cpu counting so this optimization doesn't give us
anything these days.

So let's drop the code duplication so that the code is more readable.

Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent df381975

mm/memcontrol.c

+6 −44
Original line number Diff line number Diff line
@@ -2697,52 +2697,14 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
again:

	if (*ptr) { /* css should be a valid one */

		memcg = *ptr;

		if (mem_cgroup_is_root(memcg))

			goto done;

		if (consume_stock(memcg, nr_pages))

			goto done;

		css_get(&memcg->css);

	} else {

		struct task_struct *p;



		rcu_read_lock();

		p = rcu_dereference(mm->owner);

		/*

		 * Because we don't have task_lock(), "p" can exit.

		 * In that case, "memcg" can point to root or p can be NULL with

		 * race with swapoff. Then, we have small risk of mis-accouning.

		 * But such kind of mis-account by race always happens because

		 * we don't have cgroup_mutex(). It's overkill and we allo that

		 * small race, here.

		 * (*) swapoff at el will charge against mm-struct not against

		 * task-struct. So, mm->owner can be NULL.

		 */

		memcg = mem_cgroup_from_task(p);

		if (!memcg)

			memcg = root_mem_cgroup;

		if (mem_cgroup_is_root(memcg)) {

			rcu_read_unlock();

			goto done;

		memcg = get_mem_cgroup_from_mm(mm);

	}

		if (consume_stock(memcg, nr_pages)) {

			/*

			 * It seems dagerous to access memcg without css_get().

			 * But considering how consume_stok works, it's not

			 * necessary. If consume_stock success, some charges

			 * from this memcg are cached on this cpu. So, we

			 * don't need to call css_get()/css_tryget() before

			 * calling consume_stock().

			 */

			rcu_read_unlock();

	if (mem_cgroup_is_root(memcg))

		goto done;

	if (consume_stock(memcg, nr_pages))

		goto done;

		}

		/* after here, we may be blocked. we need to get refcnt */

		if (!css_tryget(&memcg->css)) {

			rcu_read_unlock();

			goto again;

		}

		rcu_read_unlock();

	}



	do {

		bool invoke_oom = oom && !nr_oom_retries;
@@ -2778,8 +2740,8 @@ again: 


	if (batch > nr_pages)

		refill_stock(memcg, batch - nr_pages);

	css_put(&memcg->css);

done:

	css_put(&memcg->css);

	*ptr = memcg;

	return 0;

nomem:

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