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SubjectRe: OOM killer gripe (was Re: What still uses the block layer?)
Date
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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