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

KAMEZAWA Hiroyuki kamezawa.hiroyu at jp.fujitsu.com
Thu Aug 18 00:17:51 PDT 2011


On Thu, 18 Aug 2011 00:10:56 -0700
Greg Thelen <gthelen at google.com> wrote:

> KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> writes:
> 
> > On Wed, 17 Aug 2011 09:15:03 -0700
> > Greg Thelen <gthelen at 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 at 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?
> 

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






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