From: Michal Hocko <mhocko@suse.cz>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-mm@kvack.org, Hugh Dickins <hughd@google.com>,
Tejun Heo <tj@kernel.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 6/9] mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed
Date: Wed, 28 May 2014 13:31:07 +0200 [thread overview]
Message-ID: <20140528113107.GF9895@dhcp22.suse.cz> (raw)
In-Reply-To: <20140527194500.GC2878@cmpxchg.org>
On Tue 27-05-14 15:45:00, Johannes Weiner wrote:
> On Fri, May 23, 2014 at 03:20:43PM +0200, Michal Hocko wrote:
> > On Wed 30-04-14 16:25:40, Johannes Weiner wrote:
> > > There is a write barrier between setting pc->mem_cgroup and
> > > PageCgroupUsed, which was added to allow LRU operations to lookup the
> > > memcg LRU list of a page without acquiring the page_cgroup lock. But
> > > ever since 38c5d72f3ebe ("memcg: simplify LRU handling by new rule"),
> > > pages are ensured to be off-LRU while charging, so nobody else is
> > > changing LRU state while pc->mem_cgroup is being written.
> >
> > This is quite confusing. Why do we have the lrucare path then?
>
> Some charge paths start with the page on the LRU, lrucare makes sure
> it's off during the charge.
Yeah, I know I just wanted to point that the changelog might be
confusing and so mentioning this aspect would be nice...
> > The code is quite tricky so this deserves a more detailed explanation
> > IMO.
> >
> > There are only 3 paths which check both the flag and mem_cgroup (
> > without page_cgroup_lock) get_mctgt_type* and mem_cgroup_page_lruvec AFAICS.
> > None of them have rmb so there was no guarantee about ordering anyway.
>
> Yeah, exactly. As per the changelog, this is a remnant of the way it
> used to work but it's no longer needed because of guaranteed off-LRU
> state.
>
> > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> >
> > Anyway, the change is welcome
> > Acked-by: Michal Hocko <mhocko@suse.cz>
>
> Thanks!
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2014-05-28 11:31 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-30 20:25 [patch 0/9] mm: memcontrol: naturalize charge lifetime Johannes Weiner
2014-04-30 20:25 ` [patch 1/9] mm: memcontrol: fold mem_cgroup_do_charge() Johannes Weiner
2014-04-30 20:25 ` [patch 2/9] mm: memcontrol: rearrange charging fast path Johannes Weiner
2014-05-07 14:33 ` Michal Hocko
2014-05-08 18:22 ` Johannes Weiner
2014-05-12 7:59 ` Michal Hocko
2014-04-30 20:25 ` [patch 3/9] mm: memcontrol: retry reclaim for oom-disabled and __GFP_NOFAIL charges Johannes Weiner
2014-05-07 14:43 ` Michal Hocko
2014-05-08 18:28 ` Johannes Weiner
2014-04-30 20:25 ` [patch 4/9] mm: memcontrol: catch root bypass in move precharge Johannes Weiner
2014-05-07 14:55 ` Michal Hocko
2014-05-08 18:30 ` Johannes Weiner
2014-04-30 20:25 ` [patch 5/9] mm: memcontrol: use root_mem_cgroup res_counter Johannes Weiner
2014-05-07 15:14 ` Michal Hocko
2014-04-30 20:25 ` [patch 6/9] mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed Johannes Weiner
2014-05-23 13:20 ` Michal Hocko
2014-05-27 19:45 ` Johannes Weiner
2014-05-28 11:31 ` Michal Hocko [this message]
2014-04-30 20:25 ` [patch 7/9] mm: memcontrol: do not acquire page_cgroup lock for kmem pages Johannes Weiner
2014-05-23 13:39 ` Michal Hocko
2014-05-23 13:40 ` Michal Hocko
2014-05-23 14:29 ` Vladimir Davydov
2014-05-27 19:53 ` Johannes Weiner
2014-05-28 11:33 ` Michal Hocko
2014-04-30 20:25 ` [patch 8/9] mm: memcontrol: rewrite charge API Johannes Weiner
2014-05-23 14:18 ` Michal Hocko
2014-05-23 14:54 ` Michal Hocko
2014-05-23 15:18 ` Michal Hocko
2014-05-27 20:05 ` Johannes Weiner
2014-05-28 11:37 ` Michal Hocko
2014-04-30 20:25 ` [patch 9/9] mm: memcontrol: rewrite uncharge API Johannes Weiner
2014-05-04 14:32 ` Johannes Weiner
2014-05-27 7:43 ` Kamezawa Hiroyuki
2014-05-27 18:59 ` Johannes Weiner
2014-05-02 11:26 ` [patch 0/9] mm: memcontrol: naturalize charge lifetime Michal Hocko
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