From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?B?SsO2cm4=?= Engel <joern@logfs.org>
Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support)
Date: Sun, 16 Sep 2007 19:46:58 +0200
Message-ID: <20070916174657.GA2393@lazybastard.org>
References: <20070911060349.993975297@sgi.com> <200709110452.20363.nickpiggin@yahoo.com.au> <20070911121225.GE13132@lazybastard.org> <20070915014449.4f9cdb51.akpm@linux-foundation.org> <87ir6c3z2l.fsf@informatik.uni-tuebingen.de> <20070915155100.GA21861@v2.random> <87tzpvy9cb.fsf@informatik.uni-tuebingen.de> <20070915223032.GA6708@v2.random>
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Cc: Goswin von Brederlow <brederlo@informatik.uni-tuebingen.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Joern Engel <joern@logfs.org>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	Christoph Lameter <clameter@sgi.com>,
	torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Mel Gorman <mel@skynet.ie>,
	William Lee Irwin III <wli@holomorphy.com>,
	David Chinner <dgc@sgi.com>,
	Jens Axboe <jens.axboe@oracle.com>,
	Badari Pulavarty <pbadari@gmail.com>,
	Maxim Levitsky <maximlevitsky@gmail.com>,
	Fengguang Wu <fengguang.wu@gmail.com>,
	swin wang <wangswin@gmail.com>, totty.lu@gmail.com,
	hugh@veritas.com
To: Andrea Arcangeli <andrea@suse.de>
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On Sun, 16 September 2007 00:30:32 +0200, Andrea Arcangeli wrote:
>=20
> Movable? I rather assume all slab allocations aren't movable. Then
> slab defrag can try to tackle on users like dcache and inodes. Keep i=
n
> mind that with the exception of updatedb, those inodes/dentries will
> be pinned and you won't move them, which is why I prefer to consider
> them not movable too... since there's no guarantee they are.

I have been toying with the idea of having seperate caches for pinned
and movable dentries.  Downside of such a patch would be the number of
memcpy() operations when moving dentries from one cache to the other.
Upside is that a fair amount of slab cache can be made movable.
memcpy() is still faster than reading an object from disk.

Most likely the current reaction to such a patch would be to shoot it
down due to overhead, so I didn't pursue it.  All I have is an old patc=
h
to seperate never-cached from possibly-cached dentries.  It will
increase the odds of freeing a slab, but provide no guarantee.

But the point here is: dentries/inodes can be made movable if there are
clear advantages to it.  Maybe they should?

J=C3=B6rn

--=20
Joern's library part 2:
http://www.art.net/~hopkins/Don/unix-haters/tirix/embarrassing-memo.htm=
l