linux-kernel - Re: [PATCH] vmscan: improve reclaim throuput to bail out patch

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Message-ID: <2f11576a0812030712t1131c9d2x4dd0fd32eafa66ae@mail.gmail.com>
Date:	Thu, 4 Dec 2008 00:12:15 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Rik van Riel" <riel@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mel@....ul.ie
Subject: Re: [PATCH] vmscan: improve reclaim throuput to bail out patch

>> I evaluate rvr bailout and skip-freeing patch in this week conteniously.
>> I'd like to dump first output here.
>>
>>
>>
>> Rik, could you please review following?
>> ==
>> vmscan bail out patch move nr_reclaimed variable to struct scan_control.
>> Unfortunately, indirect access can easily happen cache miss.
>> More unfortunately, Some architecture (e.g. ia64) don't access global
>> variable so fast.
>
> That is amazing.  Especially considering that the scan_control
> is a local variable on the stack.

Ahhhhh, I did want to write "indirect access(or likes global variables)",
but my brain was sucked. sorry.

I'll  post description fixed version soon. thanks.


>> if heavy memory pressure happend, that's ok.
>> cache miss already plenty. it is not observable.
>>
>> but, if memory pressure is lite, performance degression is obserbable.
>
>> about 4-5% degression.
>>
>> Then, this patch introduce temporal local variable.
>
>> OK. the degression is disappeared.
>
> I can't argue with the numbers, though :)
>
> Maybe all the scanning we do ends up evicting the cache lines
> with the scan_control struct in it from the fast part of the
> CPU cache?

Yeah, I think so.


>
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>
> Acked-by: Rik van Riel <riel@...hat.com>
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