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memcg: do not replicate get_mem_cgroup_from_mm in __mem_cgroup_try_charge

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__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: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2014-04-07 15:37:44 -07:00 committed by Linus Torvalds
parent df38197546
commit b6b6cc72bc
1 changed files with 6 additions and 44 deletions
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50
mm/memcontrol.c
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@ -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;
}
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();
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();
memcg = get_mem_cgroup_from_mm(mm);
}
if (mem_cgroup_is_root(memcg))
goto done;
if (consume_stock(memcg, nr_pages))
goto done;
do {
bool invoke_oom = oom && !nr_oom_retries;
@ -2778,8 +2740,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
if (batch > nr_pages)
refill_stock(memcg, batch - nr_pages);
css_put(&memcg->css);
done:
css_put(&memcg->css);
*ptr = memcg;
return 0;
nomem: