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Message-ID: <xr93r54jtcsf.fsf@gthelen.mtv.corp.google.com>
Date: Thu, 18 Aug 2011 00:10:56 -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 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?
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