linux-kernel - Re: [PATCH 6/9] kstaled: rate limit pages scanned per second.

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Message-ID: <CANN689GFE_hqtndKY6i4ouBBe+gVU_pqOK2HRrc-U1LJMONaXw@mail.gmail.com>
Date:	Wed, 28 Sep 2011 01:19:50 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Balbir Singh <bsingharora@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Michael Wolf <mjwolf@...ibm.com>
Subject: Re: [PATCH 6/9] kstaled: rate limit pages scanned per second.

On Wed, Sep 28, 2011 at 1:13 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Tue, 27 Sep 2011 17:49:04 -0700
> Michel Lespinasse <walken@...gle.com> wrote:
>
>> Scan some number of pages from each node every second, instead of trying to
>> scan the entime memory at once and being idle for the rest of the configured
>> interval.
>>
>> In addition to spreading the CPU usage over the entire scanning interval,
>> this also reduces the jitter between two consecutive scans of the same page.
>>
>>
>> Signed-off-by: Michel Lespinasse <walken@...gle.com>
>
> Does this scan thread need to be signle thread ?

It tends to perform worse if we try making it multithreaded. What
happens is that the scanning threads call page_referenced() a lot, and
if they both try scanning pages that belong to the same file that
causes the mapping's i_mmap_mutex lock to bounce. Same things happens
if they try scanning pages that belong to the same anon VMA too.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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