Messages in this thread | | | Date | Wed, 19 Aug 2009 11:58:29 +0100 | From | Mel Gorman <> | Subject | Re: abnormal OOM killer message |
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On Wed, Aug 19, 2009 at 07:52:42PM +0900, Minchan Kim wrote: > Thanks for good comment, Mel. > > On Wed, 19 Aug 2009 11:36:11 +0100 > Mel Gorman <mel@csn.ul.ie> wrote: > > > On Wed, Aug 19, 2009 at 03:49:58PM +0900, Minchan Kim wrote: > > > On Wed, 19 Aug 2009 15:24:54 +0900 > > > ????????? <chungki.woo@gmail.com> wrote: > > > > > > > Thank you very much for replys. > > > > > > > > But I think it seems not to relate with stale data problem in compcache. > > > > My question was why last chance to allocate memory was failed. > > > > When OOM killer is executed, memory state is not a condition to > > > > execute OOM killer. > > > > Specially, there are so many pages of order 0. And allocating order is zero. > > > > I think that last allocating memory should have succeeded. > > > > That's my worry. > > > > > > Yes. I agree with you. > > > Mel. Could you give some comment in this situation ? > > > Is it possible that order 0 allocation is failed > > > even there are many pages in buddy ? > > > > > > > Not ordinarily. If it happens, I tend to suspect that the free list data > > is corrupted and would put a check in __rmqueue() that looked like > > > > BUG_ON(list_empty(&area->free_list) && area->nr_free); > > If memory is corrupt, it would be not satisfied with both condition. > It would be better to ORed condition. > > BUG_ON(list_empty(&area->free_list) || area->nr_free); >
But it's perfectly reasonable to have nr_free a positive value. The point of the check is ensure the counters make sense. If nr_free > 0 and the list is empty, it means accounting is all messed up and the values reported for "free" in the OOM message are fiction.
> > The second question is, why are we in direct reclaim this far above the > > watermark? It should only be kswapd that is doing any reclaim at that > > point. That makes me wonder again are the free lists corrupted. > > It does make sense! > > > The other possibility is that the zonelist used for allocation in the > > troubled path contains no populated zones. I would put a BUG_ON check in > > get_page_from_freelist() to check if the first zone in the zonelist has no > > pages. If that bug triggers, it might explain why OOMs are triggering for > > no good reason. > > Yes. Chungki. Could you put the both BUG_ON in each function and > try to reproduce the problem ? > > > I consider both of those possibilities abnormal though. > > > > > > > > > > ----------------------------------------------------------------------------------------------------------------------------------------------- > > > > page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order, > > > > <== this is last chance > > > > zonelist, ALLOC_WMARK_HIGH|ALLOC_CPUSET); > > > > <== uses ALLOC_WMARK_HIGH > > > > if (page) > > > > goto got_pg; > > > > > > > > out_of_memory(zonelist, gfp_mask, order); > > > > goto restart; > > > > ----------------------------------------------------------------------------------------------------------------------------------------------- > > > > > > > > > Let me have a question. > > > > > Now the system has 79M as total swap. > > > > > It's bigger than system memory size. > > > > > Is it possible in compcache? > > > > > Can we believe the number? > > > > > > > > Yeah, It's possible. 79Mbyte is data size can be swap. > > > > It's not compressed data size. It's just original data size. > > > > > > You means your pages with 79M are swap out in compcache's reserved > > > memory? > > > > > > > -- > > Mel Gorman > > Part-time Phd Student Linux Technology Center > > University of Limerick IBM Dublin Software Lab > > > -- > Kind regards, > Minchan Kim >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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