Messages in this thread Patch in this message | | | Date | Sun, 28 Jun 2009 22:22:40 +0800 | From | Wu Fengguang <> | Subject | Re: Found the commit that causes the OOMs |
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On Sun, Jun 28, 2009 at 09:36:49PM +0800, Minchan Kim wrote: > 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.
Yes, smaller inactive_anon means smaller (pointless) nr_scanned, and therefore less slab scans. Strictly speaking, it's not the fault of your patch. It indicates that the slab scan ratio algorithm should be updated too :)
We could refine the estimation of "reclaimable" pages like this:
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 416f748..e9c5b0e 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -167,14 +167,7 @@ static inline unsigned long zone_page_state(struct zone *zone, } extern unsigned long global_lru_pages(void); - -static inline unsigned long zone_lru_pages(struct zone *zone) -{ - return (zone_page_state(zone, NR_ACTIVE_ANON) - + zone_page_state(zone, NR_ACTIVE_FILE) - + zone_page_state(zone, NR_INACTIVE_ANON) - + zone_page_state(zone, NR_INACTIVE_FILE)); -} +extern unsigned long zone_lru_pages(void); #ifdef CONFIG_NUMA /* diff --git a/mm/vmscan.c b/mm/vmscan.c index 026f452..4281c6f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2123,10 +2123,31 @@ void wakeup_kswapd(struct zone *zone, int order) unsigned long global_lru_pages(void) { - return global_page_state(NR_ACTIVE_ANON) - + global_page_state(NR_ACTIVE_FILE) - + global_page_state(NR_INACTIVE_ANON) - + global_page_state(NR_INACTIVE_FILE); + int nr; + + nr = global_page_state(zone, NR_ACTIVE_FILE) + + global_page_state(zone, NR_INACTIVE_FILE); + + if (total_swap_pages) + nr += global_page_state(zone, NR_ACTIVE_ANON) + + global_page_state(zone, NR_INACTIVE_ANON); + + return nr; +} + + +unsigned long zone_lru_pages(struct zone *zone) +{ + int nr; + + nr = zone_page_state(zone, NR_ACTIVE_FILE) + + zone_page_state(zone, NR_INACTIVE_FILE); + + if (total_swap_pages) + nr += zone_page_state(zone, NR_ACTIVE_ANON) + + zone_page_state(zone, NR_INACTIVE_ANON); + + return nr; } #ifdef CONFIG_HIBERNATION -- 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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