From: Johannes Weiner <hannes@cmpxchg.org>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, jack@suse.cz,
hch@infradead.org, linux-fsdevel@vger.kernel.org,
vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, mhocko@suse.cz, clm@fb.com,
fengguang.wu@intel.com, david@fromorbit.com, gthelen@google.com,
khlebnikov@yandex-team.ru
Subject: Re: [PATCH 01/19] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online
Date: Fri, 22 May 2015 19:12:49 -0400 [thread overview]
Message-ID: <20150522231249.GA6485@cmpxchg.org> (raw)
In-Reply-To: <1432333416-6221-2-git-send-email-tj@kernel.org>
On Fri, May 22, 2015 at 06:23:18PM -0400, Tejun Heo wrote:
> cpu_possible_mask represents the CPUs which are actually possible
> during that boot instance. For systems which don't support CPU
> hotplug, this will match cpu_online_mask exactly in most cases. Even
> for systems which support CPU hotplug, the number of possible CPU
> slots is highly unlikely to diverge greatly from the number of online
> CPUs. The only cases where the difference between possible and online
> caused problems were when the boot code failed to initialize the
> possible mask and left it fully set at NR_CPUS - 1.
>
> As such, most per-cpu constructs allocate for all possible CPUs and
> often iterate over the possibles, which also has the benefit of
> avoiding the blocking CPU hotplug synchronization.
>
> memcg open codes per-cpu stat counting for mem_cgroup_read_stat() and
> mem_cgroup_read_events(), which iterates over online CPUs and handles
> CPU hotplug operations explicitly. This complexity doesn't actually
> buy anything. Switch to iterating over the possibles and drop the
> explicit CPU hotplug handling.
>
> Eventually, we want to convert memcg to use percpu_counter instead of
> its own custom implementation which also benefits from quick access
> w/o summing for cases where larger error margin is acceptable.
>
> This will allow mem_cgroup_read_stat() to be called from non-sleepable
> contexts which will be used by cgroup writeback.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
jack-AlSwsSmVLrQ@public.gmane.org,
hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org,
cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
mhocko-AlSwsSmVLrQ@public.gmane.org,
clm-b10kYP2dOMg@public.gmane.org,
fengguang.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org,
gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
khlebnikov-XoJtRXgx1JseBXzfvpsJ4g@public.gmane.org
Subject: Re: [PATCH 01/19] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online
Date: Fri, 22 May 2015 19:12:49 -0400 [thread overview]
Message-ID: <20150522231249.GA6485@cmpxchg.org> (raw)
In-Reply-To: <1432333416-6221-2-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
On Fri, May 22, 2015 at 06:23:18PM -0400, Tejun Heo wrote:
> cpu_possible_mask represents the CPUs which are actually possible
> during that boot instance. For systems which don't support CPU
> hotplug, this will match cpu_online_mask exactly in most cases. Even
> for systems which support CPU hotplug, the number of possible CPU
> slots is highly unlikely to diverge greatly from the number of online
> CPUs. The only cases where the difference between possible and online
> caused problems were when the boot code failed to initialize the
> possible mask and left it fully set at NR_CPUS - 1.
>
> As such, most per-cpu constructs allocate for all possible CPUs and
> often iterate over the possibles, which also has the benefit of
> avoiding the blocking CPU hotplug synchronization.
>
> memcg open codes per-cpu stat counting for mem_cgroup_read_stat() and
> mem_cgroup_read_events(), which iterates over online CPUs and handles
> CPU hotplug operations explicitly. This complexity doesn't actually
> buy anything. Switch to iterating over the possibles and drop the
> explicit CPU hotplug handling.
>
> Eventually, we want to convert memcg to use percpu_counter instead of
> its own custom implementation which also benefits from quick access
> w/o summing for cases where larger error margin is acceptable.
>
> This will allow mem_cgroup_read_stat() to be called from non-sleepable
> contexts which will be used by cgroup writeback.
>
> Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
Acked-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes@cmpxchg.org>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, jack@suse.cz,
hch@infradead.org, linux-fsdevel@vger.kernel.org,
vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, mhocko@suse.cz, clm@fb.com,
fengguang.wu@intel.com, david@fromorbit.com, gthelen@google.com,
khlebnikov@yandex-team.ru
Subject: Re: [PATCH 01/19] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online
Date: Fri, 22 May 2015 19:12:49 -0400 [thread overview]
Message-ID: <20150522231249.GA6485@cmpxchg.org> (raw)
In-Reply-To: <1432333416-6221-2-git-send-email-tj@kernel.org>
On Fri, May 22, 2015 at 06:23:18PM -0400, Tejun Heo wrote:
> cpu_possible_mask represents the CPUs which are actually possible
> during that boot instance. For systems which don't support CPU
> hotplug, this will match cpu_online_mask exactly in most cases. Even
> for systems which support CPU hotplug, the number of possible CPU
> slots is highly unlikely to diverge greatly from the number of online
> CPUs. The only cases where the difference between possible and online
> caused problems were when the boot code failed to initialize the
> possible mask and left it fully set at NR_CPUS - 1.
>
> As such, most per-cpu constructs allocate for all possible CPUs and
> often iterate over the possibles, which also has the benefit of
> avoiding the blocking CPU hotplug synchronization.
>
> memcg open codes per-cpu stat counting for mem_cgroup_read_stat() and
> mem_cgroup_read_events(), which iterates over online CPUs and handles
> CPU hotplug operations explicitly. This complexity doesn't actually
> buy anything. Switch to iterating over the possibles and drop the
> explicit CPU hotplug handling.
>
> Eventually, we want to convert memcg to use percpu_counter instead of
> its own custom implementation which also benefits from quick access
> w/o summing for cases where larger error margin is acceptable.
>
> This will allow mem_cgroup_read_stat() to be called from non-sleepable
> contexts which will be used by cgroup writeback.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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next prev parent reply other threads:[~2015-05-22 23:13 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-22 22:23 [PATCHSET 2/3 v3 block/for-4.2/core] writeback: cgroup writeback backpressure propagation Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 01/19] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 23:12 ` Johannes Weiner [this message]
2015-05-22 23:12 ` Johannes Weiner
2015-05-22 23:12 ` Johannes Weiner
2015-06-17 14:41 ` Michal Hocko
2015-06-17 14:41 ` Michal Hocko
2015-05-22 22:23 ` [PATCH 02/19] writeback: clean up wb_dirty_limit() Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 03/19] writeback: reorganize [__]wb_update_bandwidth() Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 04/19] writeback: implement wb_domain Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 05/19] writeback: move global_dirty_limit into wb_domain Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 06/19] writeback: consolidate dirty throttle parameters into dirty_throttle_control Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 07/19] writeback: add dirty_throttle_control->wb_bg_thresh Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 08/19] writeback: make __wb_calc_thresh() take dirty_throttle_control Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 09/19] writeback: add dirty_throttle_control->pos_ratio Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 10/19] writeback: add dirty_throttle_control->wb_completions Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 11/19] writeback: add dirty_throttle_control->dom Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 12/19] writeback: make __wb_writeout_inc() and hard_dirty_limit() take wb_domaas a parameter Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 13/19] writeback: separate out domain_dirty_limits() Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 14/19] writeback: move over_bground_thresh() to mm/page-writeback.c Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 15/19] writeback: update wb_over_bg_thresh() to use wb_domain aware operations Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 16/19] writeback: implement memcg wb_domain Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 17/19] writeback: reset wb_domain->dirty_limit[_tstmp] when memcg domain size changes Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 18/19] writeback: implement memcg writeback domain based throttling Tejun Heo
2015-05-22 22:23 ` Tejun Heo
2015-05-22 22:23 ` [PATCH 19/19] mm: vmscan: disable memcg direct reclaim stalling if cgroup writeback support is in use Tejun Heo
2015-05-22 22:23 ` Tejun Heo
-- strict thread matches above, loose matches on Subject: below --
2015-04-06 20:04 [PATCHSET 2/3 v2 block/for-4.1/core] writeback: cgroup writeback backpressure propagation Tejun Heo
2015-04-06 20:04 ` [PATCH 01/19] memcg: make mem_cgroup_read_{stat|event}() iterate possible cpus instead of online Tejun Heo
2015-04-06 20:04 ` Tejun Heo
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