From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <447A90DA.3020502@yahoo.com.au> Date: Mon, 29 May 2006 16:12:42 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH (try #3)] mm: avoid unnecessary OOM kills References: <200605230032.k4N0WCIU023760@calaveras.llnl.gov> <4472A006.2090006@yahoo.com.au> <7.0.0.16.2.20060523094646.02429fd8@llnl.gov> <44739E2D.60406@yahoo.com.au> <7.0.0.16.2.20060524073251.0237c250@llnl.gov> In-Reply-To: <7.0.0.16.2.20060524073251.0237c250@llnl.gov> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave Peterson Cc: linux-kernel@vger.kernel.org, akpm@osdl.org, pj@sgi.com, ak@suse.de, linux-mm@kvack.org, garlick@llnl.gov, mgrondona@llnl.gov List-ID: Dave Peterson wrote: > At 04:43 PM 5/23/2006, Nick Piggin wrote: >>>I agree it's desirable to keep the OOM killing logic as encapsulated >>>as possible. However unless you are holding the oom kill semaphore >>>when you make your final attempt to allocate memory it's a bit racy. >>>Holding the OOM kill semaphore guarantees that our final allocation >>>failure before invoking the OOM killer occurred _after_ any previous >>>OOM kill victim freed its memory. Thus we know we are not shooting >>>another process prematurely (i.e. before the memory-freeing effects >>>of our previous OOM kill have been felt). >> >>But there is so much fudge in it that I don't think it matters: >>pages could be freed from other sources, some reclaim might happen, >>the point at which OOM is declared is pretty arbitrary anyway, etc. > > > There's definitely some fudge in it. However the main scenario I'm > concerned with is where one big process is hogging most of the memory > (as opposed to a case where the collective memory-hogging effect of > lots of little processes triggers the OOM killer). In the first case > we want to shoot the one big process and leave the little processes > undisturbed. > > If the final allocation failure before invoking the OOM killer > occurs when we don't yet hold the OOM kill semaphore then I'd > be concerned about processes queueing up on the OOM kill semaphore > after they fail their memory allocations. If only one of these > ends up getting awakened _after_ the death of the big memory hog, > then that process will enter the OOM killer and shoot a little > process unnecessarily. > > Alternately (perhaps less likely), if your kernel is preemptible, > after the memory hog has been shot but not yet expired a process > may get preempted between its final allocation failure and its > choosing an OOM kill victim (with the memory hog expiring before > the preempted process gets rescheduled). Then the preempted > process shoots a little process when rescheduled. But just call into the oom killer, and let it queue up and/or do nothing according to whether there is still a task being shot or not. page allocation would then just try again. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com -- 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: email@kvack.org