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

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Date:	Thu, 13 Sep 2007 11:49:05 +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 Wed, Sep 12, 2007 at 01:27:33AM +1000, Nick Piggin wrote:
> > IOWs, we already play these vmap harm-minimisation games in the places
> > where we can, but still the overhead is high and something we'd prefer
> > to be able to avoid.
> 
> I don't think you've looked nearly far enough with all this low hanging
> fruit.

Ok, so we need to hack the vm to optimise it further. When it comes to
TLB flush code and optimising that sort of stuff, I'm out of my depth.

> I just gave 4 things which combined might easily reduce xfs vmap overhead
> by several orders of magnitude, all without changing much code at all.

Patches would be greatly appreciately. You obviously understand this
vm code much better than I do, so if it's easy to fix by adding some
generic vmap cache thingy, please do.

Cheers,

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