linux-kernel - Re: [patch 3/9] mm: memcontrol: retry reclaim for oom-disabled and __GFP

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Date:	Wed, 7 May 2014 16:43:39 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, Hugh Dickins <hughd@...gle.com>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/9] mm: memcontrol: retry reclaim for oom-disabled and
 __GFP_NOFAIL charges

On Wed 30-04-14 16:25:37, Johannes Weiner wrote:
> There is no reason why oom-disabled and __GFP_NOFAIL charges should
> try to reclaim only once when every other charge tries several times
> before giving up.  Make them all retry the same number of times.

I guess the idea whas that oom disabled (THP) allocation can fallback to
a smaller allocation. I would suspect this would increase latency for
THP page faults.

__GFP_NOFAIL is a different story and it can be retried.
 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
>  mm/memcontrol.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6ce59146fec7..c431a30280ac 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2589,7 +2589,7 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
>  				 bool oom)
>  {
>  	unsigned int batch = max(CHARGE_BATCH, nr_pages);
> -	int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
> +	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
>  	struct mem_cgroup *mem_over_limit;
>  	struct res_counter *fail_res;
>  	unsigned long nr_reclaimed;
> @@ -2660,6 +2660,9 @@ retry:
>  	if (mem_cgroup_wait_acct_move(mem_over_limit))
>  		goto retry;
>  
> +	if (nr_retries--)
> +		goto retry;
> +
>  	if (gfp_mask & __GFP_NOFAIL)
>  		goto bypass;
>  
> @@ -2669,9 +2672,6 @@ retry:
>  	if (!oom)
>  		goto nomem;
>  
> -	if (nr_oom_retries--)
> -		goto retry;
> -
>  	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(batch));
>  nomem:
>  	if (!(gfp_mask & __GFP_NOFAIL))
> -- 
> 1.9.2
> 

-- 
Michal Hocko
SUSE Labs
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