linux-kernel - Re: [patch 1/3] memcg: prevent endless loop when charging huge pages

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Date:	Tue, 1 Feb 2011 08:48:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	akpm@...ux-foundation.org, nishimura@....nes.nec.co.jp,
	balbir@...ux.vnet.ibm.com, minchan.kim@...il.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] memcg: prevent endless loop when charging huge
 pages

On Mon, 31 Jan 2011 15:03:53 +0100
Johannes Weiner <hannes@...xchg.org> wrote:

> The charging code can encounter a charge size that is bigger than a
> regular page in two situations: one is a batched charge to fill the
> per-cpu stocks, the other is a huge page charge.
> 
> This code is distributed over two functions, however, and only the
> outer one is aware of huge pages.  In case the charging fails, the
> inner function will tell the outer function to retry if the charge
> size is bigger than regular pages--assuming batched charging is the
> only case.  And the outer function will retry forever charging a huge
> page.
> 
> This patch makes sure the inner function can distinguish between batch
> charging and a single huge page charge.  It will only signal another
> attempt if batch charging failed, and go into regular reclaim when it
> is called on behalf of a huge page.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Thank you very much.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

> ---
>  mm/memcontrol.c |   11 +++++++++--
>  1 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d572102..73ea323 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1837,8 +1837,15 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
>  		flags |= MEM_CGROUP_RECLAIM_NOSWAP;
>  	} else
>  		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
> -
> -	if (csize > PAGE_SIZE) /* change csize and retry */
> +	/*
> +	 * csize can be either a huge page (HPAGE_SIZE), a batch of
> +	 * regular pages (CHARGE_SIZE), or a single regular page
> +	 * (PAGE_SIZE).
> +	 *
> +	 * Never reclaim on behalf of optional batching, retry with a
> +	 * single page instead.
> +	 */
> +	if (csize == CHARGE_SIZE)
>  		return CHARGE_RETRY;
>  
>  	if (!(gfp_mask & __GFP_WAIT))
> -- 
> 1.7.3.5
> 
> 

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