Messages in this thread | | | Date | Sat, 20 Dec 2008 02:08:36 +0900 | From | Daisuke Nishimura <> | Subject | Re: [bug][mmtom] memcg: MEM_CGROUP_ZSTAT underflow |
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On Fri, 19 Dec 2008 18:29:29 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Fri, 19 Dec 2008 17:29:03 +0900 > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > Hi. > > > > Current(I'm testing 2008-12-16-15-50 with some patches, though) memcg have > > MEM_CGROUP_ZSTAT underflow problem. > > > > How to reproduce: > > - make a directory, set mem.limit. > > - run some programs exceeding mem.limit. > > - make another directory, and all the tasks in old directory to new one. > > - New directory's "inactive_anon" in memory.stat underflows. > > > > From my investigation: > > - This problem seems to happen only when swapping anonymous pages. It seems > > not to happen about shmem. > > - After removing memcg-fix-swap-accounting-leak-v3.patch(and of course > > memcg-fix-swap-accounting-leak-doc-fix.patch), this problem doesn't happen. > > > > Thoughts? > > > > Thanks, then we need v4 ...but it just because my memcg-synchronized-lru.patch's > assumption about SwapCache was broken or not sane. > > It assumes pc->page_cgroup is not changed after added to LRU, but now, it changes > because it can be dropped from SwapCache and new pc->mem_cgroup can be assigned. > Maybe mem_cgroup_lru_fixup() isn't enough, now. > make sense.
> Then..could you try this ? I can't do test right now, sorry. Yes, this patch fixes the probrem.
Just a few comments. > == > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > As memcg-fix-swap-accounting-leak-v3.patch pointed out, SwapCache > can be not SwapCache before commit. > > In this case, > - the page is completely uncharged. > - but still on Old LRU. > - pc->mem_cgroup is changed before it's removed from LRU. > > For avoiding race, remove page_cgroup from old LRU before we call commit. > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > --- > mm/memcontrol.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > Index: mmotm-Dec-17/mm/memcontrol.c > =================================================================== > --- mmotm-Dec-17.orig/mm/memcontrol.c > +++ mmotm-Dec-17/mm/memcontrol.c > @@ -1152,12 +1152,27 @@ int mem_cgroup_cache_charge_swapin(struc > void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) > { > struct page_cgroup *pc; > + struct zone *zone; > > if (mem_cgroup_disabled()) > return; > if (!ptr) > return; > + > pc = lookup_page_cgroup(page); > + > + zone = page_zone(page); > + spin_lock(&zone->lru_lock); > + if (!PageSwapCache(page) && !list_empty(&pc->lru)) { list_empty check isn't necessarily needed(mem_cgroup_del_lru does it).
> + /* > + * We need to forget old LRU before modifying pc->mem_cgroup. > + * This is necessary only when the page is already uncharged > + * by delete_from_swap_cache(). > + * (Nothing happens when pc->mem_cgroup is NULL.) > + */ I think mem_cgroup_del_lru causes NULL pointer dereference bug in !pc->mem_cgroup case.
> + mem_cgroup_del_lru(page); > + } > + spin_unlock(&zone->lru_lock); > __mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED); > /* > * Now swap is on-memory. This means this page may be > @@ -1246,6 +1261,12 @@ __mem_cgroup_uncharge_common(struct page > > mem_cgroup_charge_statistics(mem, pc, false); > ClearPageCgroupUsed(pc); > + /* > + * Don't clear pc->mem_cgroup because del_from_lru() will see this. > + * The fully unchaged page is assumed to be freed after us, so it's > + * safe. When this page is reused before free, we have to be careful. > + * (In SwapCache case...it can happen.) > + */ > > mz = page_cgroup_zoneinfo(pc); > unlock_page_cgroup(pc); >
Thanks, Daisuke Nishimura.
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