Messages in this thread | | | Date | Mon, 29 May 2006 16:12:42 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH (try #3)] mm: avoid unnecessary OOM kills |
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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.
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