On Thu, 3 Jul 2014, Johannes Weiner wrote: > On Thu, Jul 03, 2014 at 12:54:36PM -0700, Hugh Dickins wrote: > > On Wed, 2 Jul 2014, Hugh Dickins wrote: > > > On Wed, 2 Jul 2014, Johannes Weiner wrote: > > > > > > > > Could you give the following patch a spin? I put it in the mmots > > > > stack on top of mm-memcontrol-rewrite-charge-api-fix-shmem_unuse-fix. > > > > > > I'm just with the laptop until this evening. I slapped it on top of > > > my 3.16-rc2-mm1 plus fixes (but obviously minus my memcg_batch one > > > - which incidentally continues to run without crashing on the G5), > > > and it quickly gave me this lockdep splat, which doesn't look very > > > different from the one before. > > > > > > I see there's now an -rc3-mm1, I'll try it out on that in half an > > > hour... but unless I send word otherwise, assume that's the same. > > > > Yes, I get that lockdep report each time on -rc3-mm1 + your patch. > > There are two instances where I missed to make &rtpz->lock IRQ-safe: > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 91b621846e10..bbaa3f4cf4db 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3919,7 +3919,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, > gfp_mask, &nr_scanned); > nr_reclaimed += reclaimed; > *total_scanned += nr_scanned; > - spin_lock(&mctz->lock); > + spin_lock_irq(&mctz->lock); > > /* > * If we failed to reclaim anything from this memory cgroup > @@ -3959,7 +3959,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, > */ > /* If excess == 0, no tree ops */ > __mem_cgroup_insert_exceeded(mz, mctz, excess); > - spin_unlock(&mctz->lock); > + spin_unlock_irq(&mctz->lock); > css_put(&mz->memcg->css); > loop++; > /* Thanks, that fixes my lockdep reports. > > That should make it complete - but the IRQ toggling costs are fairly > high so I'm rewriting the batching code to use the page lists that > most uncharges have anyway, and then batch the no-IRQ sections. Sounds good. > > > I also twice got a flurry of res_counter.c:28 underflow warnings. > > Hmm, 62 of them each time (I was checking for a number near 512, > > which would suggest a THP/4k confusion, but no). The majority > > of them coming from mem_cgroup_reparent_charges. > > I haven't seen these yet. But the location makes sense: if there are > any imbalances they'll be noticed during a group's final uncharges. I haven't seen any since adding your patch above, though I don't see how it could affect them. Of course I'll let you know if they reappear. > > > But the laptop stayed up fine (for two hours before I had to stop > > it), and the G5 has run fine with that load for 16 hours now, no > > problems with release_pages, and not even a res_counter.c:28 (but > > I don't use lockdep on it). > > Great! > > > The x86 workstation ran fine for 4.5 hours, then hit some deadlock > > which I doubt had any connection to your changes: looked more like > > a jbd2 transaction was failing to complete (which, with me trying > > ext4 on loop on tmpfs, might be more my problem than anyone else's). > > > > Oh, but nearly forgot, I did an earlier run on the laptop last night, > > which crashed within minutes on > > > > VM_BUG_ON_PAGE(!(pc->flags & PCG_MEM)) > > mm/memcontrol.c:6680! > > page had count 1 mapcount 0 mapping anon index 0x196 > > flags locked uptodate reclaim swapbacked, pcflags 1, memcg not root > > mem_cgroup_migrate < move_to_new_page < migrate_pages < compact_zone < > > compact_zone_order < try_to_compact_pages < __alloc_pages_direct_compact < > > __alloc_pages_nodemask < alloc_pages_vma < do_huge_pmd_anonymous_page < > > handle_mm_fault < __do_page_fault I got it again on the laptop, after 7 hours. > > Haven't seen that one yet, either. The only way I can see this happen > is when the same page gets selected for migration twice in a row. > Maybe a race with putback, where it gets added to the LRU but isolated > by compaction before putback drops the refcount - will verify that. Yes. This is one of those cases where I read a mail too quickly, misunderstand it, set it aside, plough through the source files, pace around thinking, finally come up with a hypothesis, go back to answer the mail, and find I've arrived at the same conclusion as you. Not verified in any way, but yes, mem_cgroup_migrate() looks anomalous to me, in clearing PCG_MEM and PGC_MEMSW but leaving PCG_USED. Once that old page is put back on LRU for freeing, it could get isolated by another migrator, who discovers the anomalous state in its own mem_cgroup_migrate(). mem_cgroup_migrate() should just set pc->flags = 0, shouldn't it? But is there any point to PCG_USED now? Couldn't PageCgroupUsed (or better, PageCgroupCharged) just test PCG_MEM and PCG_MEMSW? Which should be low bits of pc->mem_cgroup, halving the array. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>