From: Hugh Dickins <hughd@google.com>
To: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Ying Han <yinghan@google.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 6/10] mm/memcg: take care over pc->mem_cgroup
Date: Tue, 21 Feb 2012 12:00:08 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.00.1202211140330.1858@eggly.anvils> (raw)
In-Reply-To: <4F433418.3010401@openvz.org>
On Tue, 21 Feb 2012, Konstantin Khlebnikov wrote:
> >
> > Be particularly careful in compaction's isolate_migratepages() and
> > vmscan's lumpy handling in isolate_lru_pages(): those approach the
> > page by its physical location, and so can encounter pages which
> > would not be found by any logical lookup. For those cases we have
> > to change __isolate_lru_page() slightly: it must leave ClearPageLRU
> > to the caller, because compaction and lumpy cannot safely interfere
> > with a page until they have first isolated it and then locked lruvec.
>
> Yeah, this is most complicated part.
Yes, I found myself leaving this patch until last when commenting.
And was not entirely convinced by what I then said of move_account().
Indeed, I wondered if it might be improved and simplified by taking
lruvec locks itself, in the manner that commit_charge lrucare ends
up doing.
> I found one race here, see below.
Thank you!
> > @@ -386,10 +364,24 @@ static isolate_migrate_t isolate_migrate
> > continue;
> >
> > page_relock_lruvec(page,&lruvec);
>
> Here race with mem_cgroup_move_account() we hold lock for old lruvec,
> while move_account() recharge page and put page back into other lruvec.
> Thus we see PageLRU(), but below we isolate page from wrong lruvec.
I expect you'll prove right on that, but I'm going to think about it
more later.
>
> In my patch-set this is fixed with __wait_lru_unlock() [ spin_unlock_wait() ]
> in mem_cgroup_move_account()
Right now, after finishing mail, I want to concentrate on getting your
series working under my swapping load.
It's possible that I screwed up rediffing it to my slightly later
base (though the only parts that appeared to need fixing up were as
expected, near update_isolated_counts and move_active_pages_to_lru);
but if so I'd expect that to show up differently.
At present, although it runs fine with cgroup_disable=memory, with memcg
two machines very soon hit that BUG at include/linux/mm_inline.h:41!
when the lru_size or pages_count wraps around; on another it hit that
precisely when I stopped the test.
In all cases it's in release_pages from free_pages_and_swap_cache from
tlb_flush_mmu from tlb_finish_mmu from exit_mmap from mmput from exit_mm
from do_exit (but different processes exiting).
Hugh
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next prev parent reply other threads:[~2012-02-21 20:00 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-20 23:26 [PATCH 0/10] mm/memcg: per-memcg per-zone lru locking Hugh Dickins
2012-02-20 23:28 ` [PATCH 1/10] mm/memcg: scanning_global_lru means mem_cgroup_disabled Hugh Dickins
2012-02-21 8:03 ` KAMEZAWA Hiroyuki
2012-02-20 23:29 ` [PATCH 2/10] mm/memcg: move reclaim_stat into lruvec Hugh Dickins
2012-02-21 8:05 ` KAMEZAWA Hiroyuki
2012-02-20 23:30 ` [PATCH 3/10] mm/memcg: add zone pointer " Hugh Dickins
2012-02-21 8:08 ` KAMEZAWA Hiroyuki
2012-02-20 23:32 ` [PATCH 4/10] mm/memcg: apply add/del_page to lruvec Hugh Dickins
2012-02-21 8:20 ` KAMEZAWA Hiroyuki
2012-02-21 22:25 ` Hugh Dickins
2012-02-20 23:33 ` [PATCH 5/10] mm/memcg: introduce page_relock_lruvec Hugh Dickins
2012-02-21 8:38 ` KAMEZAWA Hiroyuki
2012-02-21 22:36 ` Hugh Dickins
2012-02-20 23:34 ` [PATCH 6/10] mm/memcg: take care over pc->mem_cgroup Hugh Dickins
2012-02-21 5:55 ` Konstantin Khlebnikov
2012-02-21 19:37 ` Hugh Dickins
2012-02-21 20:40 ` Konstantin Khlebnikov
2012-02-21 22:05 ` Hugh Dickins
2012-02-21 6:05 ` Konstantin Khlebnikov
2012-02-21 20:00 ` Hugh Dickins [this message]
2012-02-21 9:13 ` KAMEZAWA Hiroyuki
2012-02-21 23:03 ` Hugh Dickins
2012-02-22 4:05 ` Konstantin Khlebnikov
2012-02-20 23:35 ` [PATCH 7/10] mm/memcg: remove mem_cgroup_reset_owner Hugh Dickins
2012-02-21 9:17 ` KAMEZAWA Hiroyuki
2012-02-20 23:36 ` [PATCH 8/10] mm/memcg: nest lru_lock inside page_cgroup lock Hugh Dickins
2012-02-21 9:48 ` KAMEZAWA Hiroyuki
2012-02-20 23:38 ` [PATCH 9/10] mm/memcg: move lru_lock into lruvec Hugh Dickins
2012-02-21 7:08 ` Konstantin Khlebnikov
2012-02-21 20:12 ` Hugh Dickins
2012-02-21 21:35 ` Konstantin Khlebnikov
2012-02-21 22:12 ` Hugh Dickins
2012-02-22 3:43 ` Konstantin Khlebnikov
2012-02-22 6:09 ` Hugh Dickins
2012-02-23 14:21 ` Konstantin Khlebnikov
2012-02-20 23:39 ` [PATCH 10/10] mm/memcg: per-memcg per-zone lru locking Hugh Dickins
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