linux-kernel - Re: [PATCH 0/3] compressed in-memory swapping take5

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Message-ID: <49D400A5.20901@vflare.org>
Date:	Thu, 02 Apr 2009 05:32:45 +0530
From:	Nitin Gupta <nitingupta910@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	penberg@...helsinki.fi, cl@...ux-foundation.org, edt@....ca,
	linux-mm-cc@...top.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] compressed in-memory swapping take5

Hi Andrew,

Thanks for your reply. My comments inline.

Andrew Morton wrote:

>>   - Links to more performance numbers, use cases can be found at:
>> http://lkml.org/lkml/2009/3/17/116
> 
> The sole, whole, entire point of this patchset is performance.  Yet
> after chasing a few scruffy links, the only data we have to justify
> merging _any_ of this stuff is, and I quote,
> 
>  - The time of paging down one pdf page was reduced to 1/4~1/100
>  - The time of switching from one firefox tab to another was reduced to 1/6
>  - The capacity of kpdf was be increased from 2 pdf files to 11 pdf files.
>  - The capacity of firefox was increased from 6 web pages to 15 web pages.
> 
> that isn't very compelling!
> 
> So would it be possible for you to come up with some more concrete
> testing results to help convince us that we should make this change to
> Linux?  And include them front-and-centre in the changelog, and
> maintain it?
>

Fair enough. I will get these numbers and include them in changelog itself.
Probably by next kernel release.

> We would also be interested in seeing the performance _loss_ from these
> patches.  There must be some cost somewhere.  Find a worstish-case test
> case and run it and include its results in the changelog too, so we
> better understand the tradeoffs involved here.
> 

Sure. I will get these too.

> 
> I'm really reluctant to go and merge a complete new memory allocator
> just on behalf of an obscure driver.  Oh well, perhaps hiding it down
> in drivers/block was the right thing to do.


Justification for this custom allocator is present in xvmalloc changelog
itself. It gives reason for not using SLUB and SLOB. During review
cycle, I never got any arguments against that justification.

For possible inclusion in Linux, I will hide it in drivers/block/ramzswap
and rename interfaces to make sure that no-one else can use it.

> 
> As the patchset adds five tightly-related files, perhaps it should all
> live in drivers/block/rmazswap/?
> 
> 

Ok, no problem.


Thanks for reply.
Nitin

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