Messages in this thread | | | Date | Wed, 19 Aug 2009 21:06:41 +0900 | Subject | Re: abnormal OOM killer message | From | Chungki woo <> |
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On Wed, Aug 19, 2009 at 7:58 PM, Mel Gorman<mel@csn.ul.ie> wrote: > 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! >
'Corrupted free list' makes sense. Thank you very much. Inserting BUG_ON code is also good idea to check corruption of free list.
I have one more question. As you know, before and after executing direct reclaim routine(try_to_free_pages) cond_resched() routine is also executed. In other words, it can be scheduled at that time. Is there no possibility executing kswapd or try_to_free_pages at other context at that time? I think this fact maybe can explain that gap(between watermark and free memory) also. How do you think about this? But I know this can't explain why last chance to allocate memory was failed. I think your idea makes sense.
Anyway, I will try to test again with following BUG_ON code.
BUG_ON(list_empty(&area->free_list) && area->nr_free);
Thanks Mel, Minchan
>> > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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