linux-kernel - Re: OOM killer gripe (was Re: What still uses the block layer?)

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Message-Id: <200710161859.55325.rob@landley.net>
Date:	Tue, 16 Oct 2007 18:59:54 -0500
From:	Rob Landley <rob@...dley.net>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Theodore Tso <tytso@....edu>,
	James Bottomley <James.Bottomley@...eleye.com>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Nick Piggin <piggin@...erone.com.au>
Subject: Re: OOM killer gripe (was Re: What still uses the block layer?)

On Tuesday 16 October 2007 5:28:59 am Alan Cox wrote:
> > I'm sure somebody will eventually write an OLS paper or something on the
> > advisability of making swapping decisions with 4k granularity when disks
> > really want bigger I/O transactions.
>
> Funnily enough someone thought of that many years ago. They even added
> and documented it, then they made it adjustable.
>
> See the vm section of Documentation/filesystems/proc.txt

I presume you refer to:

  page-cluster
  ------------

  page-cluster controls the number of pages which are written to swap in
  a single attempt.  The swap I/O size.

  It is a logarithmic value - setting it to zero means "1 page", setting
  it to 1 means "2 pages", setting it to 2 means "4 pages", etc.

  The default value is three (eight pages at a time).  There may be some
  small benefits in tuning this to a different value if your workload is
  swap-intensive.

I didn't know that controlled whether the pages were contiguous (or written to 
contiguous locations in swap).  I thought it was just how many the VM tried 
to free at a time.

Still, worth a tweak.  Thanks.

> Alan

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.
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