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To: linux-kernel@vger.kernel.org
From: torvalds@transmeta.com (Linus Torvalds)
Subject: Re: large file IO starving ls -l
Date: Sat, 3 Aug 2002 22:53:12 +0000 (UTC)
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References: <Pine.LNX.4.44.0208032253260.23040-100000@pc40.e18.physik.tu-muenchen.de>
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In article <Pine.LNX.4.44.0208032253260.23040-100000@pc40.e18.physik.tu-muenchen.de>,
Roland Kuhn  <rkuhn@e18.physik.tu-muenchen.de> wrote:
>
>Now the question is: who keeps ls from returning? The command never hits 
>the disk (reads in above histogram do not increase), but stays for many 
>seconds (up to one minute) in state D.

ext2 used to have similar issues with the superblock lock - where things
like block allocation (very much in the write path) would grab the
superblock lock, and completely destroy interactive feel even for
processes that didn't need to do IO, because the superblock lock was
often grabbed even if the data was actually cached (sb locking needed
just to _look_up_ the physical block so that you could look up the
cached data in the buffer cache). 

Al Viro largely fixed in for ext2, which now uses lock_super() a lot
less. But a lot of filesystems are based on the old ext2 locking, and
may have inherited some of the worst parts..

		Linus
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