linux-kernel - Re: [PATCH mmotm/next] memcg-mm-introduce-lowlimit-reclaim-fix2.patch

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Date:	Tue, 27 May 2014 15:01:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH mmotm/next]
 memcg-mm-introduce-lowlimit-reclaim-fix2.patch

On Tue, 27 May 2014 14:36:04 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:

> mem_cgroup_within_guarantee() oopses in _raw_spin_lock_irqsave() when
> booted with cgroup_disable=memory.  Fix that in the obvious inelegant
> way for now - though I hope we are moving towards a world in which
> almost all of the mem_cgroup_disabled() tests will vanish, with a
> root_mem_cgroup which can handle the basics even when disabled.
> 
> I bet there's a neater way of doing this, rearranging the loop (and we
> shall want to avoid spinlocking on root_mem_cgroup when we reach that
> new world), but that's the kind of thing I'd get wrong in a hurry!
> 
> ...
>
> @@ -2793,6 +2793,9 @@ static struct mem_cgroup *mem_cgroup_loo
>  bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg,
>  		struct mem_cgroup *root)
>  {
> +	if (mem_cgroup_disabled())
> +		return false;
> +
>  	do {
>  		if (!res_counter_low_limit_excess(&memcg->res))
>  			return true;

This seems to be an awfully late and deep place at which to be noticing
mem_cgroup_disabled().  Should mem_cgroup_within_guarantee() even be called
in this state?
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