Re: [PATCH v9 11/13] writeback: make background writeback cgroupaware
From: KAMEZAWA Hiroyuki
Date: Thu Aug 18 2011 - 03:43:31 EST
On Thu, 18 Aug 2011 00:38:49 -0700
Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes:
>
> > On Thu, 18 Aug 2011 00:10:56 -0700
> > Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> >
> >> KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes:
> >>
> >> > On Wed, 17 Aug 2011 09:15:03 -0700
> >> > Greg Thelen <gthelen@xxxxxxxxxx> 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@xxxxxxxxxx>
> >> >> ---
> >> >> 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;
>
Ah, I see. Thank you for clarification.
Thanks,
-Kame
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