Messages in this thread | | | Date | Sun, 28 Jun 2009 22:36:49 +0900 | Subject | Re: Found the commit that causes the OOMs | From | Minchan Kim <> |
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On Sun, Jun 28, 2009 at 10:30 PM, Minchan Kim<minchan.kim@gmail.com> wrote: > HI, Wu. > > On Sun, Jun 28, 2009 at 8:32 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: >> On Sat, Jun 27, 2009 at 08:54:12PM +0800, Johannes Weiner wrote: >>> On Sat, Jun 27, 2009 at 08:12:49AM +0100, David Howells wrote: >>> > >>> > I've managed to bisect things to find the commit that causes the OOMs. It's: >>> > >>> > commit 69c854817566db82c362797b4a6521d0b00fe1d8 >>> > Author: MinChan Kim <minchan.kim@gmail.com> >>> > Date: Tue Jun 16 15:32:44 2009 -0700 >>> > >>> > vmscan: prevent shrinking of active anon lru list in case of no swap space V3 >>> > >>> > shrink_zone() can deactivate active anon pages even if we don't have a >>> > swap device. Many embedded products don't have a swap device. So the >>> > deactivation of anon pages is unnecessary. >>> > >>> > This patch prevents unnecessary deactivation of anon lru pages. But, it >>> > don't prevent aging of anon pages to swap out. >>> > >>> > Signed-off-by: Minchan Kim <minchan.kim@gmail.com> >>> > Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> >>> > Cc: Johannes Weiner <hannes@cmpxchg.org> >>> > Acked-by: Rik van Riel <riel@redhat.com> >>> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> >>> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> >>> > >>> > This exhibits the problem. The previous commit: >>> > >>> > commit 35282a2de4e5e4e173ab61aa9d7015886021a821 >>> > Author: Brice Goglin <Brice.Goglin@ens-lyon.org> >>> > Date: Tue Jun 16 15:32:43 2009 -0700 >>> > >>> > migration: only migrate_prep() once per move_pages() >>> > >>> > survives 16 iterations of the LTP syscall testsuite without exhibiting the >>> > problem. >>> >>> Here is the patch in question: >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 7592d8e..879d034 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1570,7 +1570,7 @@ static void shrink_zone(int priority, struct zone *zone, >>> * Even if we did not try to evict anon pages at all, we want to >>> * rebalance the anon lru active/inactive ratio. >>> */ >>> - if (inactive_anon_is_low(zone, sc)) >>> + if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0) >>> shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); >>> >>> throttle_vm_writeout(sc->gfp_mask); >>> >>> When this was discussed, I think we missed that nr_swap_pages can >>> actually get zero on swap systems as well and this should have been >>> total_swap_pages - otherwise we also stop balancing the two anon lists >>> when swap is _full_ which was not the intention of this change at all. >> >> Exactly. In Jesse's OOM case, the swap is exhausted. >> total_swap_pages is the better choice in this situation. >> >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426766] Active_anon:290797 active_file:28 inactive_anon:97034 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426767] inactive_file:61 unevictable:11322 dirty:0 writeback:0 unstable:0 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426768] free:3341 slab:13776 mapped:5880 pagetables:6851 bounce:0 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426772] DMA free:7776kB min:40kB low:48kB high:60kB active_anon:556kB inactive_anon:524kB >> +active_file:16kB inactive_file:0kB unevictable:0kB present:15340kB pages_scanned:30 all_unreclaimable? no >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426775] lowmem_reserve[]: 0 1935 1935 1935 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426781] DMA32 free:5588kB min:5608kB low:7008kB high:8412kB active_anon:1162632kB >> +inactive_anon:387612kB active_file:96kB inactive_file:256kB unevictable:45288kB present:1982128kB pages_scanned:980 >> +all_unreclaimable? no >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426784] lowmem_reserve[]: 0 0 0 0 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426787] DMA: 64*4kB 77*8kB 45*16kB 18*32kB 4*64kB 2*128kB 2*256kB 3*512kB 1*1024kB >> +1*2048kB 0*4096kB = 7800kB >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426796] DMA32: 871*4kB 149*8kB 1*16kB 2*32kB 1*64kB 0*128kB 1*256kB 1*512kB 0*1024kB >> +0*2048kB 0*4096kB = 5588kB >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426804] 151250 total pagecache pages >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426806] 18973 pages in swap cache >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426808] Swap cache stats: add 610640, delete 591667, find 144356/181468 >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426810] Free swap = 0kB >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.426811] Total swap = 979956kB >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.434828] 507136 pages RAM >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.434831] 23325 pages reserved >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.434832] 190892 pages shared >> Jun 18 07:44:53 jbarnes-g45 kernel: [64377.434833] 248816 pages non-shared >> >> >> In David's OOM case, there are two symptoms: >> 1) 70000 unaccounted/leaked pages as found by Andrew >> (plus rather big number of PG_buddy and pagetable pages) >> 2) almost zero active_file/inactive_file; small inactive_anon; >> many slab and active_anon pages. >> >> In the situation of (2), the slab cache is _under_ scanned. So David >> got OOM when vmscan should have squeezed some free pages from the slab >> cache. Which is one important side effect of MinChan's patch? > > My patch's side effect is (2). > > My guessing is following as. > > 1. The number of page scanned in shrink_slab is increased in shrink_page_list. > And it is doubled for mapped page or swapcache. > 2. shrink_page_list is called by shrink_inactive_list > 3. shrink_inactive_list is called by shrink_list > > Look at the shrink_list. > If inactive lru list is low, it always call shrink_active_list not > shrink_inactive_list in case of anon.
I missed most important point. My patch's side effect is that it keeps inactive anon's lru low. So I think it is caused by my patch's side effect.
> It means it doesn't increased sc->nr_scanned. > Then shrink_slab can't shrink enough slab pages. > So, David OOM have a lot of slab pages and active anon pages. > > Does it make sense ? > If it make sense, we have to change shrink_slab's pressure method. > What do you think ? > > > -- > Kinds regards, > Minchan Kim >
-- Kinds regards, Minchan Kim -- 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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