linux-ext4 - Re: page fault scalability (ext3, ext4, xfs)

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Date:	Wed, 14 Aug 2013 13:50:02 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Theodore Ts'o <tytso@....edu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-fsdevel@...r.kernel.org, xfs@....sgi.com,
	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>, david@...morbit.com,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: page fault scalability (ext3, ext4, xfs)

On 08/14/2013 12:43 PM, Theodore Ts'o wrote:
> Thanks dave for doing this comparison.  Is there any chance you can
> check whether lockstats shows anything interesting?
> 
>> Test case is this:
>>
>> 	https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault3.c
> 
> One interesting thing about the test case.  It looks like the first
> time through the while loop, the file will need to be extended (since
> it is a new tempfile).  But subsequent times through the list the
> blocks for the file will already be allocated.  If the file is
> prezero'ed ahead of time, so we're only measuring the cost of the
> write page fault, and we take block allocation out of the comparison,
> do we see the same scalability curve?

Would a plain old fallocate() do the trick, or does it actually need
zeros written to it?

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