From: Mel Gorman <mgorman@suse.de>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vlastimil Babka <vbabka@suse.cz>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 7/9] mm, page_alloc: remove stop_machine from build_all_zonelists
Date: Fri, 14 Jul 2017 13:47:43 +0100 [thread overview]
Message-ID: <20170714124743.jhvobgvxj3nv45cb@suse.de> (raw)
In-Reply-To: <20170714110025.GG2618@dhcp22.suse.cz>
On Fri, Jul 14, 2017 at 01:00:25PM +0200, Michal Hocko wrote:
> On Fri 14-07-17 10:59:32, Mel Gorman wrote:
> > On Fri, Jul 14, 2017 at 10:00:04AM +0200, Michal Hocko wrote:
> > > From: Michal Hocko <mhocko@suse.com>
> > >
> > > build_all_zonelists has been (ab)using stop_machine to make sure that
> > > zonelists do not change while somebody is looking at them. This is
> > > is just a gross hack because a) it complicates the context from which
> > > we can call build_all_zonelists (see 3f906ba23689 ("mm/memory-hotplug:
> > > switch locking to a percpu rwsem")) and b) is is not really necessary
> > > especially after "mm, page_alloc: simplify zonelist initialization".
> > >
> > > Updates of the zonelists happen very seldom, basically only when a zone
> > > becomes populated during memory online or when it loses all the memory
> > > during offline. A racing iteration over zonelists could either miss a
> > > zone or try to work on one zone twice. Both of these are something we
> > > can live with occasionally because there will always be at least one
> > > zone visible so we are not likely to fail allocation too easily for
> > > example.
> > >
> > > Signed-off-by: Michal Hocko <mhocko@suse.com>
> >
> > This patch is contingent on the last patch which updates in place
> > instead of zeroing the early part of the zonelist first but needs to fix
> > the stack usage issues. I think it's also worth pointing out in the
> > changelog that stop_machine never gave the guarantees it claimed as a
> > process iterating through the zonelist can be stopped so when it resumes
> > the zonelist has changed underneath it. Doing it online is roughly
> > equivalent in terms of safety.
>
> OK, what about the following addendum?
> "
> Please note that the original stop_machine approach doesn't really
> provide a better exclusion because the iteration might be interrupted
> half way (unless the whole iteration is preempt disabled which is not the
> case in most cases) so the some zones could still be seen twice or a
> zone missed.
> "
Works for me.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2017-07-14 12:47 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-14 7:59 [PATCH 0/9] cleanup zonelists initialization Michal Hocko
2017-07-14 7:59 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko
2017-07-14 9:36 ` Mel Gorman
2017-07-14 10:47 ` Michal Hocko
2017-07-14 11:16 ` Mel Gorman
2017-07-14 11:38 ` Michal Hocko
2017-07-14 12:56 ` Mel Gorman
2017-07-14 13:01 ` Mel Gorman
2017-07-14 13:08 ` Michal Hocko
2017-07-19 9:33 ` Vlastimil Babka
2017-07-19 13:44 ` Michal Hocko
2017-07-14 7:59 ` [PATCH 2/9] mm, page_alloc: remove boot pageset initialization from memory hotplug Michal Hocko
2017-07-14 9:39 ` Mel Gorman
2017-07-19 13:15 ` Vlastimil Babka
2017-07-14 8:00 ` [PATCH 3/9] mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization Michal Hocko
2017-07-14 9:48 ` Mel Gorman
2017-07-14 10:50 ` Michal Hocko
2017-07-14 12:32 ` Mel Gorman
2017-07-14 12:39 ` Michal Hocko
2017-07-14 12:56 ` Mel Gorman
2017-07-19 13:19 ` Vlastimil Babka
2017-07-14 8:00 ` [PATCH 4/9] mm, memory_hotplug: drop zone from build_all_zonelists Michal Hocko
2017-07-19 13:33 ` Vlastimil Babka
2017-07-20 8:15 ` Michal Hocko
2017-07-14 8:00 ` [PATCH 5/9] mm, memory_hotplug: remove explicit build_all_zonelists from try_online_node Michal Hocko
2017-07-14 12:14 ` Michal Hocko
2017-07-20 6:13 ` Vlastimil Babka
2017-07-14 8:00 ` [PATCH 6/9] mm, page_alloc: simplify zonelist initialization Michal Hocko
2017-07-14 9:55 ` Mel Gorman
2017-07-14 10:51 ` Michal Hocko
2017-07-14 12:46 ` Mel Gorman
2017-07-14 13:02 ` Michal Hocko
2017-07-14 14:18 ` Mel Gorman
2017-07-17 6:06 ` Michal Hocko
2017-07-17 8:07 ` Mel Gorman
2017-07-17 8:19 ` Michal Hocko
2017-07-17 8:58 ` Mel Gorman
2017-07-17 9:15 ` Michal Hocko
2017-07-20 6:55 ` Vlastimil Babka
2017-07-20 7:19 ` Michal Hocko
2017-07-14 8:00 ` [PATCH 7/9] mm, page_alloc: remove stop_machine from build_all_zonelists Michal Hocko
2017-07-14 9:59 ` Mel Gorman
2017-07-14 11:00 ` Michal Hocko
2017-07-14 12:47 ` Mel Gorman [this message]
2017-07-14 11:29 ` Vlastimil Babka
2017-07-14 11:43 ` Michal Hocko
2017-07-14 11:45 ` Michal Hocko
2017-07-20 6:16 ` Vlastimil Babka
2017-07-20 7:24 ` Vlastimil Babka
2017-07-20 9:21 ` Michal Hocko
2017-07-14 8:00 ` [PATCH 8/9] mm, memory_hotplug: get rid of zonelists_mutex Michal Hocko
2017-07-14 8:00 ` [PATCH 9/9] mm, sparse, page_ext: drop ugly N_HIGH_MEMORY branches for allocations Michal Hocko
2017-07-20 8:04 ` Vlastimil Babka
2017-07-21 14:39 [PATCH -v1 0/9] cleanup zonelists initialization Michal Hocko
2017-07-21 14:39 ` [PATCH 7/9] mm, page_alloc: remove stop_machine from build_all_zonelists Michal Hocko
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