linux-kernel - Re: [00/41] Large Blocksize Support V7 (adds memmap support)

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Date:	Thu, 13 Sep 2007 12:01:45 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	David Chinner <dgc@....com>
Cc:	Mel Gorman <mel@...net.ie>, Christoph Lameter <clameter@....com>,
	andrea@...e.de, torvalds@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@....de>,
	William Lee Irwin III <wli@...omorphy.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Badari Pulavarty <pbadari@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Fengguang Wu <fengguang.wu@...il.com>,
	swin wang <wangswin@...il.com>, totty.lu@...il.com,
	hugh@...itas.com, joern@...ybastard.org
Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support)

On Thursday 13 September 2007 23:03, David Chinner wrote:
> On Thu, Sep 13, 2007 at 03:23:21AM +1000, Nick Piggin wrote:

> > Well, it may not be easy to _fix_, but it's easy to try a few
> > improvements ;)
> >
> > How do I make an image and run a workload that will coerce XFS into
> > doing a significant number of vmaps?
>
> # mkfs.xfs -n size=16384 <dev>
>
> to create a filesystem with a 16k directory block size on a 4k page
> machine.
>
> Then just do operations on directories with lots of files in them
> (tens of thousands). Every directory operation will require at
> least one vmap in this situation - e.g. a traversal will result in
> lots and lots of blocks being read that will require vmap() for every
> directory block read from disk and an unmap almost immediately
> afterwards when the reference is dropped....

Ah, wow, thanks: I can reproduce it.
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