Lukas Czerner <lczer...@redhat.com> writes:
> Currently there is not limitation of number of requests in the loop bio
> list. This can lead into some nasty situations when the caller spawns
> tons of bio requests taking huge amount of memory. This is even more
> obvious with discard where blkdev_issue_discard() will submit all bios
> for the range and wait for them to finish afterwards. On really big loop
> devices this can lead to OOM situation as reported by Dave Chinner.
>
> With this patch we will wait in loop_make_request() if the number of
> bios in the loop bio list would exceed 'nr_requests' number of requests.
> We'll wake up the process as we process the bios form the list.
I think you might want to do something similar to what is done for
request_queues by implementing a congestion on and off threshold. As
Jens writes in this commit (predating the conversion to git):
Author: Jens Axboe <ax...@suse.de>
Date: Wed Nov 3 15:47:37 2004 -0800
[PATCH] queue congestion threshold hysteresis
We need to open the gap between congestion on/off a little bit, or
we risk burning many cycles continually putting processes on a wait
queue only to wake them up again immediately. This was observed with
CFQ at least, which showed way excessive sys time.
Patch is from Arjan.
Signed-off-by: Jens Axboe <ax...@suse.de>
Signed-off-by: Linus Torvalds <torva...@osdl.org>
If you feel this isn't necessary, then I think you at least need to
justify it with testing. Perhaps Jens can shed some light on the exact
workload that triggered the pathological behaviour.
Cheers,
Jeff
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