linux-kernel - Re: block cache replacement strategy?

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Date:	Mon, 13 Sep 2010 17:21:38 +0200
From:	Johannes Stezenbach <js@...21.net>
To:	Florian Mickler <florian@...kler.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: block cache replacement strategy?

On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote:
> 
> Linear read heuristic might be a good guess, but it would
> be nice to hear a comment from a vm/fs expert which
> confirms this works as intended.

Apparently I'm unworthy to get a response from someone knowledgable :-(

Anyway I found lmdd (from lmbench) can do random reads,
and indeed causes the data to enter the block (page?) cache,
replacing the previous data.


Johannes


zzz:~# echo 3 >/proc/sys/vm/drop_caches

zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000
1000.0000 MB in 17.7554 secs, 56.3210 MB/sec
zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000
1000.0000 MB in 0.9112 secs, 1097.4178 MB/sec

zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
norepeat on 238035072
norepeat on 724579648
1000.0000 MB in 21.4419 secs, 46.6376 MB/sec
zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
norepeat on 238035072
norepeat on 724579648
1000.0000 MB in 14.3859 secs, 69.5125 MB/sec
zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
norepeat on 238035072
norepeat on 724579648
1000.0000 MB in 0.8764 secs, 1141.0810 MB/sec
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