linux-kernel - Re: What is the limit size of tmpfs /dev/shm ?

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Message-ID: <47AA102F.1070105@zytor.com>
Date:	Wed, 06 Feb 2008 11:53:19 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Tomasz Chmielewski <mangoo@...g.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mika Lawando <rzryyvzy@...shmail.net>
Subject: Re: What is the limit size of tmpfs /dev/shm ?

Hugh Dickins wrote:
> 
> In theory, yes, and should be true in practice before it hits swap.
> But I think you'll find our swap handling is too primitive for tmpfs
> to perform well once we hit swap.  Most filesystems pay considerable
> attention to good performance within their constraints of correctness.
> Whereas with tmpfs we've just never worried about the performance once
> swapping.  It's used so you don't lose your data, but if you're really
> expecting to be going to disk very much, better start with a filesystem
> really designed for that.
> 

That sounds like a problem in our overall swap handling, not 
specifically in tmpfs.  Now, I can't say anything concrete about heavy 
swap conditions, but in light swap conditions I have measured a 20x 
performance improvement(!) over ext3 on real workloads.

	-hpa
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