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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: David Chinner <dgc@sgi.com>
Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support)
Date: Thu, 13 Sep 2007 12:01:45 +1000
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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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