From linux-mm Sun Aug 29 20:59:17 2004 From: Andrew Morton Date: Sun, 29 Aug 2004 20:59:17 +0000 To: linux-mm Subject: Re: Kernel 2.6.8.1: swap storm of death - nr_requests > 1024 on Message-Id: <20040829135917.3e8ffed8.akpm () osdl ! org> X-MARC-Message: https://marc.info/?l=linux-mm&m=109381333610167 Jens Axboe wrote: > > > That was my point. > > I didn't understand your message at all, maybe that wasn't clear enough > in my email :-). You state that the main effect of that particular patch > is to bump nr_requests to 8192, which is definitely not true. The main > effect of the patch is to make sure that ->nr_requests was valid, so > that cfqd->max_queued is valid. ->nr_requests was always overwritten > with 8192 for quite some time, irregardless of that patch. So this > particular change has nothing to do with that, and other io schedulers > will experience exactly this very problem with 8192 requests. > > Why you do see a difference is that when ->max_queued isn't valid, you > end up block a lot more in get_request_wait() because cfq_may_queue will > disallow you to queue a lot more than with the patch. Since other io > schedulers don't have these sort of checks, they behave like CFQ does > with the bug in blk_init_queue() fixed. The changlog wasn't that detailed ;) But yes, it's the large nr_requests which is tripping up swapout. I'm assuming that when a process exits with its anonymous memory still under swap I/O we're forgetting to actually free the pages when the I/O completes. So we end up with a ton of zero-ref swapcache pages on the LRU. I assume. Something odd's happening, that's for sure. -- 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: aart@kvack.org