Re: 2.4.20: Proccess stuck in __lock_page ...

[Matthias Mueller]

On Thu, May 29, 2003 at 03:55:08PM +0200, 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 run fluxbox, not a very heavy window manager, but I installed ctwm and
tried again with vanilla 2.4.20. If I disabled swap the short hangs (1s) are
gone, but the long mouse hangs (10s) are still there.

Matthias
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