Re: Kernel 2.6.8.1: swap storm of death - nr_requests > 1024 on swap partition

On Sun, Aug 29 2004, Jens Axboe wrote:

quoted

It's all very bizarre.

If you do a big `usemem -m 250' on a 256MB box, you end up with all memory
in swapcache _after_ usemem exits.  That's wrong: all the memory which
usemem allocated should now be free.

But all that swapcache is reclaimable under memory pressure.  It seems to
be floating about on the LRU still.

It only happens with the CFQ elevator, and this backout patch makes it go
away.

It's not bizarre, if you backout that fix (it is a fix!), ->nr_requests
isn't initialized when cfq gets there. So it'll throttle incorrectly in
may_queue, not a good idea.

Oh, and I think the main issue is the vm. It should cope correctly no
matter how much pending memory can be in progress on the queue, else it
should not write out so much. CFQ is just exposing this bug because it
defaults to bigger nr_requests.

-- 
Jens Axboe

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>