linux-kernel - Re: Per-user swap devices.

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Message-ID: <44BE78C0.4020909@mauve.plus.com>
Date:	Wed, 19 Jul 2006 19:24:00 +0100
From:	Ian Stirling <ian.stirling@...ve.plus.com>
To:	Valdis.Kletnieks@...edu
CC:	linux-kernel@...r.kernel.org
Subject: Re: Per-user swap devices.

Valdis.Kletnieks@...edu wrote:
> On Wed, 19 Jul 2006 10:54:38 BST, Ian Stirling said:
> 
>>It would be really nice to be able to simply: chown crashalot.users 
>>/dev/swap0 ;swapon /dev/swap0
>>Then anything run by crashalot would swap to /dev/swap0 - and not locally.

> This doesn't look like it will do as much good as you think.  The problem
> is what to do when something run by some *other* UID needs a page - you need
> to fix the code to preferentially steal a page from a 'crashalot' process.
> 
> And at that point, what you probably want instead is a global per-UID RSS
> limit.  This looks like a job for a CKRM resource class controller rather than
> a hack to the swap code.

Not quite.
I've got one set of users that I care about their processes never dying
root, ..., and another set that I don't.

I want them to contend for real RAM as normal - it's quite acceptible to 
me for users in the second group to push root/...s web-proxy, screen 
session, processes far into slow local swap. Most of these processes 
will be not very interactive - but I don't want them to die.

If the fast (but unreliable) swap device dies - I'm quite happy for my 
firefox and mplayer processes to die - but not my window manager or 
whatever. RSS limits don't address this.

The only way I can think of to address this is to somehow segregate swap 
devices.
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