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Date: Thu, 2 Nov 2000 17:37:27 -0800
From: Jens Axboe <axboe@suse.de>
To: Val Henson <vhenson@esscom.com>
Cc: Mike Galbraith <mikeg@wen-online.de>, Rik van Riel <riel@conectiva.com.br>,
        linux-kernel@vger.kernel.org
Subject: Re: [BUG] /proc/<pid>/stat access stalls badly for swapping process, 2.4.0-test10
Message-ID: <20001102173727.C11439@suse.de>
In-Reply-To: <Pine.LNX.4.21.0011011643050.6740-100000@duckman.distro.conectiva> <Pine.Linu.4.10.10011020800010.1299-100000@mikeg.weiden.de> <20001102145912.B8472@esscom.com>
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In-Reply-To: <20001102145912.B8472@esscom.com>; from vhenson@esscom.com on Thu, Nov 02, 2000 at 02:59:12PM -0700
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On Thu, Nov 02 2000, Val Henson wrote:
> > > 3) combine this with the elevator starvation stuff (ask Jens
> > >    Axboe for blk-7 to alleviate this issue) and you have a
> > >    scenario where processes using /proc/<pid>/stat have the
> > >    possibility to block on multiple processes that are in the
> > >    process of handling a page fault (but are being starved)
> > 
> > I'm experimenting with blk.[67] in test10 right now.  The stalls
> > are not helped at all.  It doesn't seem to become request bound
> > (haven't instrumented that yet to be sure) but the stalls persist.
> > 
> > 	-Mike
> 
> This is not an elevator starvation problem.

True, but the blk-xx patches help work-around (what I believe) is
bad flushing behaviour by the vm.

> I also experienced these stalls with my IDE-only system.  Unless I'm
> badly mistaken, the elevator is only used on SCSI disks, therefore
> elevator starvation cannot be blamed for this problem.  These stalls
> are particularly annoying since I want to find the pid of the process
> hogging memory in order to kill it, but the read from /proc stalls for
> 45 seconds or more.

You are badly mistaken.

-- 
* Jens Axboe <axboe@suse.de>
* SuSE Labs
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