From: Con Kolivas <kernel@kolivas.org>
To: Willy Tarreau <willy@w.ods.org>, Andrea Arcangeli <andrea@suse.de>
Subject: Re: 2.4.20: Proccess stuck in __lock_page ...
Date: Fri, 30 May 2003 00:09:37 +1000
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Cc: Andrew Morton <akpm@digeo.com>,
       Matthias Mueller <matthias.mueller@rz.uni-karlsruhe.de>, axboe@suse.de,
       m.c.p@wolk-project.de, manish@storadinc.com, marcelo@conectiva.com.br,
       linux-kernel@vger.kernel.org
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On Thu, 29 May 2003 23:55, Willy Tarreau wrote:
> Hello !
>
> I've done a few tests with -rc6 on my dev machine (dual xp 1.5G, 512 MB,
> scsi). It's the *FIRST* time I have ever seen my mouse cursor hang (just a
> little bit however, and totally acceptable) ! Usually, my kernel include
> -aa VM and lowlat patches, and I've never encountered this behaviour on
> this machine with such a configuration. However, with stock kernel, I admit
> that during the 2 minutes it takes to write the 2G file, I see the mouse
> stick two or three times during about 1 second, which is quite acceptable
> IMHO. Opening an xterm may take 10s to get to the prompt (more annoying).
> Same to launch 'ps'.
>
> I use a fairly simple window manager (ctwm), which doesn't access the disk
> once it's launched. It never gets stuck during all the operation if I
> disable the swap. If I enable the swap, it sometimes takes one or two
> seconds to draw a menu. The swap is used up to about 4 MB.
>
> I then tried -rc6 with ll_rw_blk from -rc5, and it's worse, even with swap
> disabled. The hangs happen more often, but are about the same durations. So
> I confirm that -rc6 is better here than -rc5.
>
> I retried with rc4aa1, and everything went very smooth again ; it takes at
> most 1 second to get an xterm with the prompt ready, and ps responds
> immediately. So I think that there are two things here:
>   - those who experience very long hangs may use a heavy window manager
>     which does continuous disk accesses (I mean it accesses the disk for
> any simple operation).
>   - a hungry WM may also be swapped during such operations, rendering it
>     totally unusable, particularly if the swap is on the same physical disk
>     as the file being written to.
>
> So, could the people who report long hangs retry with swap disabled ?
> Can we limit the amount of memory consummed by the cache during such a
> write ?

I still get hangs with rc6 with massive writeouts to swap. The problem was 
that I was getting hangs without writeouts to swap with 2.4.19pre1 
->2.4.21pre5. I didn't expect the patch backout to suddenly make writing to 
swap occur for free (although that would be nice).

Con
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