Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 12/12] oom: give current access to memory reserves if it has been killed | Date | Tue, 8 Jun 2010 20:41:51 +0900 (JST) |
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> From: David Rientjes <rientjes@google.com> > > It's possible to livelock the page allocator if a thread has > mm->mmap_sem and fails to make forward progress because the > oom killer selects another thread sharing the same ->mm to > kill that cannot exit until the semaphore is dropped. > > The oom killer will not kill multiple tasks at the same time; each oom > killed task must exit before another task may be killed. Thus, if one > thread is holding mm->mmap_sem and cannot allocate memory, all threads > sharing the same ->mm are blocked from exiting as well. In the oom kill > case, that means the thread holding mm->mmap_sem will never free > additional memory since it cannot get access to memory reserves and the > thread that depends on it with access to memory reserves cannot exit > because it cannot acquire the semaphore. Thus, the page allocators > livelocks. > > When the oom killer is called and current happens to have a pending > SIGKILL, this patch automatically gives it access to memory reserves and > returns. Upon returning to the page allocator, its allocation will > hopefully succeed so it can quickly exit and free its memory. If not, > the page allocator will fail the allocation if it is not __GFP_NOFAIL. > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > Signed-off-by: David Rientjes <rientjes@google.com> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > --- > mm/oom_kill.c | 10 ++++++++++ > 1 files changed, 10 insertions(+), 0 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 67b5fa5..ad85e1b 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -638,6 +638,16 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, > } > > /* > + * If current has a pending SIGKILL, then automatically select it. The > + * goal is to allow it to allocate so that it may quickly exit and free > + * its memory. > + */ > + if (fatal_signal_pending(current)) { > + set_tsk_thread_flag(current, TIF_MEMDIE); > + return; > + }
Self NAK this. We have no gurantee that current is oom killable. Oh, here is out_of_memory(), sigh.
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