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Date: Thu, 18 Aug 2011 00:38:49 -0700
From: Greg Thelen <gthelen@...gle.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
containers@...ts.osdl.org, linux-fsdevel@...r.kernel.org,
Balbir Singh <bsingharora@...il.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Minchan Kim <minchan.kim@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Wu Fengguang <fengguang.wu@...el.com>,
Dave Chinner <david@...morbit.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andrea Righi <andrea@...terlinux.com>,
Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v9 11/13] writeback: make background writeback cgroup aware
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
> On Thu, 18 Aug 2011 00:10:56 -0700
> Greg Thelen <gthelen@...gle.com> wrote:
>
>> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
>>
>> > On Wed, 17 Aug 2011 09:15:03 -0700
>> > Greg Thelen <gthelen@...gle.com> wrote:
>> >
>> >> When the system is under background dirty memory threshold but some
>> >> cgroups are over their background dirty memory thresholds, then only
>> >> writeback inodes associated with the over-limit cgroups.
>> >>
>> >> In addition to checking if the system dirty memory usage is over the
>> >> system background threshold, over_bground_thresh() now checks if any
>> >> cgroups are over their respective background dirty memory thresholds.
>> >>
>> >> If over-limit cgroups are found, then the new
>> >> wb_writeback_work.for_cgroup field is set to distinguish between system
>> >> and memcg overages. The new wb_writeback_work.shared_inodes field is
>> >> also set. Inodes written by multiple cgroup are marked owned by
>> >> I_MEMCG_SHARED rather than a particular cgroup. Such shared inodes
>> >> cannot easily be attributed to a cgroup, so per-cgroup writeback
>> >> (futures version of wakeup_flusher_threads and balance_dirty_pages)
>> >> performs suboptimally in the presence of shared inodes. Therefore,
>> >> write shared inodes when performing cgroup background writeback.
>> >>
>> >> If performing cgroup writeback, move_expired_inodes() skips inodes that
>> >> do not contribute dirty pages to the cgroup being written back.
>> >>
>> >> After writing some pages, wb_writeback() will call
>> >> mem_cgroup_writeback_done() to update the set of over-bg-limits memcg.
>> >>
>> >> This change also makes wakeup_flusher_threads() memcg aware so that
>> >> per-cgroup try_to_free_pages() is able to operate more efficiently
>> >> without having to write pages of foreign containers. This change adds a
>> >> mem_cgroup parameter to wakeup_flusher_threads() to allow callers,
>> >> especially try_to_free_pages() and foreground writeback from
>> >> balance_dirty_pages(), to specify a particular cgroup to write inodes
>> >> from.
>> >>
>> >> Signed-off-by: Greg Thelen <gthelen@...gle.com>
>> >> ---
>> >> Changelog since v8:
>> >>
>> >> - Added optional memcg parameter to __bdi_start_writeback(),
>> >> bdi_start_writeback(), wakeup_flusher_threads(), writeback_inodes_wb().
>> >>
>> >> - move_expired_inodes() now uses pass in struct wb_writeback_work instead of
>> >> struct writeback_control.
>> >>
>> >> - Added comments to over_bground_thresh().
>> >>
>> >> fs/buffer.c | 2 +-
>> >> fs/fs-writeback.c | 96 +++++++++++++++++++++++++++++++++-----------
>> >> fs/sync.c | 2 +-
>> >> include/linux/writeback.h | 6 ++-
>> >> mm/backing-dev.c | 3 +-
>> >> mm/page-writeback.c | 3 +-
>> >> mm/vmscan.c | 3 +-
>> >> 7 files changed, 84 insertions(+), 31 deletions(-)
>> >>
>> >> diff --git a/fs/buffer.c b/fs/buffer.c
>> >> index dd0220b..da1fb23 100644
>> >> --- a/fs/buffer.c
>> >> +++ b/fs/buffer.c
>> >> @@ -293,7 +293,7 @@ static void free_more_memory(void)
>> >> struct zone *zone;
>> >> int nid;
>> >>
>> >> - wakeup_flusher_threads(1024);
>> >> + wakeup_flusher_threads(1024, NULL);
>> >> yield();
>> >>
>> >> for_each_online_node(nid) {
>> >> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> >> index e91fb82..ba55336 100644
>> >> --- a/fs/fs-writeback.c
>> >> +++ b/fs/fs-writeback.c
>> >> @@ -38,10 +38,14 @@ struct wb_writeback_work {
>> >> struct super_block *sb;
>> >> unsigned long *older_than_this;
>> >> enum writeback_sync_modes sync_mode;
>> >> + unsigned short memcg_id; /* If non-zero, then writeback specified
>> >> + * cgroup. */
>> >> unsigned int tagged_writepages:1;
>> >> unsigned int for_kupdate:1;
>> >> unsigned int range_cyclic:1;
>> >> unsigned int for_background:1;
>> >> + unsigned int for_cgroup:1; /* cgroup writeback */
>> >> + unsigned int shared_inodes:1; /* write inodes spanning cgroups */
>> >>
>> >> struct list_head list; /* pending work list */
>> >> struct completion *done; /* set if the caller waits */
>> >> @@ -114,9 +118,12 @@ static void bdi_queue_work(struct backing_dev_info *bdi,
>> >> spin_unlock_bh(&bdi->wb_lock);
>> >> }
>> >>
>> >> +/*
>> >> + * @memcg is optional. If set, then limit writeback to the specified cgroup.
>> >> + */
>> >> static void
>> >> __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
>> >> - bool range_cyclic)
>> >> + bool range_cyclic, struct mem_cgroup *memcg)
>> >> {
>> >> struct wb_writeback_work *work;
>> >>
>> >> @@ -136,6 +143,8 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
>> >> work->sync_mode = WB_SYNC_NONE;
>> >> work->nr_pages = nr_pages;
>> >> work->range_cyclic = range_cyclic;
>> >> + work->memcg_id = memcg ? css_id(mem_cgroup_css(memcg)) : 0;
>> >> + work->for_cgroup = memcg != NULL;
>> >>
>> >
>> >
>> > I couldn't find a patch for mem_cgroup_css(NULL). Is it in patch 1-10 ?
>> > Other parts seems ok to me.
>> >
>> >
>> > Thanks,
>> > -Kame
>>
>> Mainline commit d324236b3333e87c8825b35f2104184734020d35 adds
>> mem_cgroup_css() to memcontrol.c. The above code does not call
>> mem_cgroup_css() with a NULL parameter due to the 'memcg ? ...' check.
>> So I do not think any additional changes to mem_cgroup_css() are needed.
>> Am I missing your point?
>>
>
> I thought you need
> ==
> struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem)
> {
> + if (!mem)
> + return NULL;
> return &mem->css;
> }
> ==
> And
> ==
> unsigned short css_id(struct cgroup_subsys_state *css)
> {
> struct css_id *cssid;
>
> + if (!css)
> return 0;
> }
> ==
>
> Thanks,
> -Kame
I think that your changes to mem_cgroup_css() and css_id() are
unnecessary for my patches because my patches do not call
mem_cgroup_css(NULL). The "?" check below prevents NULL from being
passed into mem_cgroup_css():
+ work->memcg_id = memcg ? css_id(mem_cgroup_css(memcg)) : 0;
--
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