Re: [PATCH v9 11/13] writeback: make background writeback cgroup aware

[Greg Thelen <gthelen@google.com>]

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:

> On Wed, 17 Aug 2011 09:15:03 -0700
> Greg Thelen <gthelen@google.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@google.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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