Message-ID: <4DDB74F7.9020109@jp.fujitsu.com>
Date: Tue, 24 May 2011 18:05:59 +0900
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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To: mgorman@suse.de
CC: minchan.kim@gmail.com, abarry@cray.com, akpm@linux-foundation.org,
        linux-mm@kvack.org, riel@redhat.com, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org
Subject: Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc:
 patch.
References: <4DCDA347.9080207@cray.com> <BANLkTikiXUzbsUkzaKZsZg+5ugruA2JdMA@mail.gmail.com> <4DD2991B.5040707@cray.com> <BANLkTimYEs315jjY9OZsL6--mRq3O_zbDA@mail.gmail.com> <20110520164924.GB2386@barrios-desktop> <4DDB3A1E.6090206@jp.fujitsu.com> <20110524083008.GA5279@suse.de> <4DDB6DF6.2050700@jp.fujitsu.com> <20110524084915.GC5279@suse.de>
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>>> Why?
>>
>> Otherwise, we don't have good PCP dropping trigger. Big machine might have
>> big pcp cache.
>>
> 
> Big machines also have a large cost for sending IPIs.

Yes. But it's only matter if IPIs are frequently happen.
But, drain_all_pages() is NOT only IPI source. some vmscan function (e.g.
try_to_umap) makes a lot of IPIs.

Then, it's _relatively_ not costly. I have a question. Do you compare which
operation and drain_all_pages()? IOW, your "costly" mean which scenario suspect?


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