linux-kernel - Re: 2.6 tmpfs/swap performance oddity

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Date:	Wed, 06 Dec 2006 15:51:34 -0500
From:	Phillip Susi <psusi@....rr.com>
To:	"Magnus Naeslund(k)" <mag@...e.se>
CC:	linux-kernel@...r.kernel.org
Subject: Re: 2.6 tmpfs/swap performance oddity

Magnus Naeslund(k) wrote:
> But tmpfs seems to get really slow when it has to swap out stuff from
> tmp to a 80 gb swap partition, much slower than just writing a file
> to the ext3 fs. Maybe this is a known thing, and easily tuned, but
> I've not seen any solutions when googling around.

This is a SWAG ( Silly Wild Ass Guess ), but maybe tmpfs isn't mapping 
the files sequentially in ram, or is otherwise doing something to 
prevent proper swap clustering and read ahead?

> Somehow I think I'm missing something here, maybe we're not supposed
> to use tmpfs in this way at all? What more information can I supply
> to narrow down the problem? Is there any secret knobs that I can use
> to tune swap performance?

You aren't supposed to be using tmpfs in this way at all ;)

tmpfs is meant to hold small files that will only exist for a short 
time, or do not need to persist after a reboot.  Keep your big data 
files on a normal filesystem, and let the kernel worry about caching the 
most frequently accessed parts.

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