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

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Date:	Wed, 06 Feb 2008 14:01:36 -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:
> On Wed, 6 Feb 2008, H. Peter Anvin wrote:
>> 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.
> 
> Wow, I'm surprised.  I suppose I do jump to thinking of heavy swapping
> when light swapping won't be so bad; but even so, 20x ext3 astonishes
> me - ext3 wouldn't be anyone's choice for fastest, but even so...
> 
> I certainly guess too much and measure too little:
> is there a useful test you could point me to?  TIA
> 

The specific application was this:

- extract a kernel tarball
- "make distclean"
- cp -al the resulting tree
- apply a patch to each tree
- do a diff between the trees
- delete all files

... repeat something like 20,000 times.

	-hpa
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