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

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Date:	Mon, 17 Sep 2007 14:07:10 +1000
From:	David Chinner <dgc@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	David Chinner <dgc@....com>, 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 Fri, Sep 14, 2007 at 06:48:55AM +1000, Nick Piggin wrote:
> On Thursday 13 September 2007 12:01, Nick Piggin wrote:
> > On Thursday 13 September 2007 23:03, David Chinner wrote:
> > > 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.
> 
> OK, the vunmap batching code wipes your TLB flushing and IPIs off
> the table. Diffstat below, but the TLB portions are here (besides that
> _everything_ is probably lower due to less TLB misses caused by the
> TLB flushing):
> 
>       -170   -99.4% sn2_send_IPI
>       -343  -100.0% sn_send_IPI_phys
>     -17911   -99.9% smp_call_function
>
> Total performance went up by 30% on a 64-way system (248 seconds to
> 172 seconds to run parallel finds over different huge directories).

Good start, Nick ;)

> 
>      23012  54790.5% _read_lock
>       9427   329.0% __get_vm_area_node
>       5792     0.0% __find_vm_area
>       1590  53000.0% __vunmap
....

_read_lock? I though vmap() and vunmap() only took the vmlist_lock in
write mode.....

> Next I have some patches to scale the vmap locks and data
> structures better, but they're not quite ready yet. This looks like it
> should result in a further speedup of several times when combined
> with the TLB flushing reductions here...

Sounds promising - when you have patches that work, send them my
way and I'll run some tests on them.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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