linux-kernel - Re: [PATCH] VM: Implements the swap-out page-clustering technique

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Message-ID: <48C78246.7050507@gmail.com>
Date:	Wed, 10 Sep 2008 11:46:06 +0330
From:	"Hamid R. Jahanjou" <hamid.jahanjou@...il.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Zan Lynx <zlynx@....org>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VM: Implements the swap-out page-clustering technique

Rik van Riel wrote:
> On Sun, 07 Sep 2008 18:28:30 -0600
> Zan Lynx <zlynx@....org> wrote:
>   
>> Rik van Riel wrote:
>> [cut]
>>     
>>> On the other hand, you do want to avoid evicting data 
>>> that the process is still using, just because you are 
>>> swapping out a not recently referenced page on a
>>> nearby virtual address.
>>>       
>> How about writing the nearby pages to swap anyway and mark the still 
>> in-use pages as SwapCache.
>>     
>
> That is what will happen pretty much automatically.
>   

I agree. As you said, we have two conflicting requirements here: on the
one hand one likes to swap as many pages as to satisfy the backing
storage "proper block IO size," on the other hand, one should not make a
process lose too many pages.  The code needs tuning really, I'm going to
rewrite it making it more flexible according to the suggestion given on
the mailing list.

> Another thing the swap out page clustering code could
> do is move pages that were recently referenced back
> to the active list, so the VM will not have to scan
> those pages again.
>
>   

I think this is a very good idea, actually the code does this already.

Thanks.
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