linux-kernel - Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

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Message-ID: <4C17815A.8080402@redhat.com>
Date:	Tue, 15 Jun 2010 09:34:18 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

On 06/15/2010 07:45 AM, Mel Gorman wrote:
> On Mon, Jun 14, 2010 at 05:55:51PM -0400, Rik van Riel wrote:
>> On 06/14/2010 07:17 AM, Mel Gorman wrote:
>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index 4856a2a..574e816 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -372,6 +372,12 @@ int write_reclaim_page(struct page *page, struct address_space *mapping,
>>>    	return PAGE_SUCCESS;
>>>    }
>>>
>>> +/* kswapd and memcg can writeback as they are unlikely to overflow stack */
>>> +static inline bool reclaim_can_writeback(struct scan_control *sc)
>>> +{
>>> +	return current_is_kswapd() || sc->mem_cgroup != NULL;
>>> +}
>>> +
>>
>> I'm not entirely convinced on this bit, but am willing to
>> be convinced by the data.
>>
>
> Which bit?
>
> You're not convinced that kswapd should be allowed to write back?
> You're not convinced that memcg should be allowed to write back?
> You're not convinced that direct reclaim writing back pages can overflow
> 	the stack?

If direct reclaim can overflow the stack, so can direct
memcg reclaim.  That means this patch does not solve the
stack overflow, while admitting that we do need the
ability to get specific pages flushed to disk from the
pageout code.

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