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Date: Wed, 8 Jun 2011 09:01:32 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Greg Thelen <gthelen@...gle.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,
Andrea Righi <arighi@...eler.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Minchan Kim <minchan.kim@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Wu Fengguang <fengguang.wu@...el.com>,
Vivek Goyal <vgoyal@...hat.com>,
Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v8 10/12] memcg: create support routines for
page-writeback
On Tue, 07 Jun 2011 08:58:16 -0700
Greg Thelen <gthelen@...gle.com> wrote:
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
>
> > On Fri, 3 Jun 2011 09:12:16 -0700
> > Greg Thelen <gthelen@...gle.com> wrote:
> >
> >> Introduce memcg routines to assist in per-memcg dirty page management:
> >>
> >> - mem_cgroup_balance_dirty_pages() walks a memcg hierarchy comparing
> >> dirty memory usage against memcg foreground and background thresholds.
> >> If an over-background-threshold memcg is found, then per-memcg
> >> background writeback is queued. Per-memcg writeback differs from
> >> classic, non-memcg, per bdi writeback by setting the new
> >> writeback_control.for_cgroup bit.
> >>
> >> If an over-foreground-threshold memcg is found, then foreground
> >> writeout occurs. When performing foreground writeout, first consider
> >> inodes exclusive to the memcg. If unable to make enough progress,
> >> then consider inodes shared between memcg. Such cross-memcg inode
> >> sharing likely to be rare in situations that use per-cgroup memory
> >> isolation. The approach tries to handle the common (non-shared)
> >> case well without punishing well behaved (non-sharing) cgroups.
> >> As a last resort writeback shared inodes.
> >>
> >> This routine is used by balance_dirty_pages() in a later change.
> >>
> >> - mem_cgroup_hierarchical_dirty_info() returns the dirty memory usage
> >> and limits of the memcg closest to (or over) its dirty limit. This
> >> will be used by throttle_vm_writeout() in a latter change.
> >>
> >> Signed-off-by: Greg Thelen <gthelen@...gle.com>
> >> ---
> >> Changelog since v7:
> >> - Add more detail to commit description.
> >>
> >> - Declare the new writeback_control for_cgroup bit in this change, the
> >> first patch that uses the new field is first used. In -v7 the field
> >> was declared in a separate patch.
> >>
> >> include/linux/memcontrol.h | 18 +++++
> >> include/linux/writeback.h | 1 +
> >> include/trace/events/memcontrol.h | 83 ++++++++++++++++++++
> >> mm/memcontrol.c | 150 +++++++++++++++++++++++++++++++++++++
> >> 4 files changed, 252 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> >> index 3d72e09..0d0363e 100644
> >> --- a/include/linux/memcontrol.h
> >> +++ b/include/linux/memcontrol.h
> >> @@ -167,6 +167,11 @@ bool should_writeback_mem_cgroup_inode(struct inode *inode,
> >> struct writeback_control *wbc);
> >> bool mem_cgroups_over_bground_dirty_thresh(void);
> >> void mem_cgroup_writeback_done(void);
> >> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
> >> + struct mem_cgroup *mem,
> >> + struct dirty_info *info);
> >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
> >> + unsigned long write_chunk);
> >>
> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> >> gfp_t gfp_mask,
> >> @@ -383,6 +388,19 @@ static inline void mem_cgroup_writeback_done(void)
> >> {
> >> }
> >>
> >> +static inline void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
> >> + unsigned long write_chunk)
> >> +{
> >> +}
> >> +
> >> +static inline bool
> >> +mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
> >> + struct mem_cgroup *mem,
> >> + struct dirty_info *info)
> >> +{
> >> + return false;
> >> +}
> >> +
> >> static inline
> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> >> gfp_t gfp_mask,
> >> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> >> index 66ec339..4f5c0d2 100644
> >> --- a/include/linux/writeback.h
> >> +++ b/include/linux/writeback.h
> >> @@ -47,6 +47,7 @@ struct writeback_control {
> >> unsigned for_reclaim:1; /* Invoked from the page allocator */
> >> unsigned range_cyclic:1; /* range_start is cyclic */
> >> unsigned more_io:1; /* more io to be dispatched */
> >> + unsigned for_cgroup:1; /* enable cgroup writeback */
> >> unsigned shared_inodes:1; /* write inodes spanning cgroups */
> >> };
> >>
> >> diff --git a/include/trace/events/memcontrol.h b/include/trace/events/memcontrol.h
> >> index 326a66b..b42dae1 100644
> >> --- a/include/trace/events/memcontrol.h
> >> +++ b/include/trace/events/memcontrol.h
> >> @@ -109,6 +109,89 @@ TRACE_EVENT(mem_cgroups_over_bground_dirty_thresh,
> >> __entry->first_id)
> >> )
> >>
> >> +DECLARE_EVENT_CLASS(mem_cgroup_consider_writeback,
> >> + TP_PROTO(unsigned short css_id,
> >> + struct backing_dev_info *bdi,
> >> + unsigned long nr_reclaimable,
> >> + unsigned long thresh,
> >> + bool over_limit),
> >> +
> >> + TP_ARGS(css_id, bdi, nr_reclaimable, thresh, over_limit),
> >> +
> >> + TP_STRUCT__entry(
> >> + __field(unsigned short, css_id)
> >> + __field(struct backing_dev_info *, bdi)
> >> + __field(unsigned long, nr_reclaimable)
> >> + __field(unsigned long, thresh)
> >> + __field(bool, over_limit)
> >> + ),
> >> +
> >> + TP_fast_assign(
> >> + __entry->css_id = css_id;
> >> + __entry->bdi = bdi;
> >> + __entry->nr_reclaimable = nr_reclaimable;
> >> + __entry->thresh = thresh;
> >> + __entry->over_limit = over_limit;
> >> + ),
> >> +
> >> + TP_printk("css_id=%d bdi=%p nr_reclaimable=%ld thresh=%ld "
> >> + "over_limit=%d", __entry->css_id, __entry->bdi,
> >> + __entry->nr_reclaimable, __entry->thresh, __entry->over_limit)
> >> +)
> >> +
> >> +#define DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(name) \
> >> +DEFINE_EVENT(mem_cgroup_consider_writeback, name, \
> >> + TP_PROTO(unsigned short id, \
> >> + struct backing_dev_info *bdi, \
> >> + unsigned long nr_reclaimable, \
> >> + unsigned long thresh, \
> >> + bool over_limit), \
> >> + TP_ARGS(id, bdi, nr_reclaimable, thresh, over_limit) \
> >> +)
> >> +
> >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_bg_writeback);
> >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_fg_writeback);
> >> +
> >> +TRACE_EVENT(mem_cgroup_fg_writeback,
> >> + TP_PROTO(unsigned long write_chunk,
> >> + struct writeback_control *wbc),
> >> +
> >> + TP_ARGS(write_chunk, wbc),
> >> +
> >> + TP_STRUCT__entry(
> >> + __field(unsigned long, write_chunk)
> >> + __field(long, wbc_to_write)
> >> + __field(bool, shared_inodes)
> >> + ),
> >> +
> >> + TP_fast_assign(
> >> + __entry->write_chunk = write_chunk;
> >> + __entry->wbc_to_write = wbc->nr_to_write;
> >> + __entry->shared_inodes = wbc->shared_inodes;
> >> + ),
> >> +
> >> + TP_printk("write_chunk=%ld nr_to_write=%ld shared_inodes=%d",
> >> + __entry->write_chunk,
> >> + __entry->wbc_to_write,
> >> + __entry->shared_inodes)
> >> +)
> >> +
> >> +TRACE_EVENT(mem_cgroup_enable_shared_writeback,
> >> + TP_PROTO(unsigned short css_id),
> >> +
> >> + TP_ARGS(css_id),
> >> +
> >> + TP_STRUCT__entry(
> >> + __field(unsigned short, css_id)
> >> + ),
> >> +
> >> + TP_fast_assign(
> >> + __entry->css_id = css_id;
> >> + ),
> >> +
> >> + TP_printk("enabling shared writeback for memcg %d", __entry->css_id)
> >> +)
> >> +
> >> #endif /* _TRACE_MEMCONTROL_H */
> >>
> >> /* This part must be outside protection */
> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> >> index a5b1794..17cb888 100644
> >> --- a/mm/memcontrol.c
> >> +++ b/mm/memcontrol.c
> >> @@ -1622,6 +1622,156 @@ void mem_cgroup_writeback_done(void)
> >> }
> >> }
> >>
> >> +/*
> >> + * This routine must be called by processes which are generating dirty pages.
> >> + * It considers the dirty pages usage and thresholds of the current cgroup and
> >> + * (depending if hierarchical accounting is enabled) ancestral memcg. If any of
> >> + * the considered memcg are over their background dirty limit, then background
> >> + * writeback is queued. If any are over the foreground dirty limit then
> >> + * throttle the dirtying task while writing dirty data. The per-memcg dirty
> >> + * limits check by this routine are distinct from either the per-system,
> >> + * per-bdi, or per-task limits considered by balance_dirty_pages().
> >> + */
> >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
> >> + unsigned long write_chunk)
> >> +{
> >> + struct backing_dev_info *bdi = mapping->backing_dev_info;
> >> + struct mem_cgroup *mem;
> >> + struct mem_cgroup *ref_mem;
> >> + struct dirty_info info;
> >> + unsigned long nr_reclaimable;
> >> + unsigned long sys_available_mem;
> >> + unsigned long pause = 1;
> >> + unsigned short id;
> >> + bool over;
> >> + bool shared_inodes;
> >> +
> >> + if (mem_cgroup_disabled())
> >> + return;
> >> +
> >> + sys_available_mem = determine_dirtyable_memory();
> >> +
> >> + /* reference the memcg so it is not deleted during this routine */
> >> + rcu_read_lock();
> >> + mem = mem_cgroup_from_task(current);
> >> + if (mem && mem_cgroup_is_root(mem))
> >> + mem = NULL;
> >> + if (mem)
> >> + css_get(&mem->css);
> >> + rcu_read_unlock();
> >> + ref_mem = mem;
> >> +
> >> + /* balance entire ancestry of current's mem. */
> >> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) {
> >> + id = css_id(&mem->css);
> >> +
> >
> > Hmm, this sounds natural...but...don't we need to restart checking from ref_mem's
> > dirty_ratio once we find an ancestor is over dirty_ratio and we slept ?
> >
> > Even if parent's dirty ratio comes to be clean state, children's may not.
> > So, I think some "restart loop" jump after io_schedule_timeout().
> >
> > Thanks,
> > -Kame
>
> I do not think that we need to restart, but maybe you have a case in
> mind that I am not considering.
>
> Example hierarchy:
> root
> A B
> A1 A2
> A11 A12 A21 A22
>
> Assume that mem_cgroup_balance_dirty_pages(A11), so ref_mem=A11.
>
> We start at A11 and walk up towards the root. If A11 is over limit,
> then write A11 until under limit. Next check A1, if over limit then
> write A1,A11,A12. Then check A. If A is over A limit, then we invoke
> writeback on A* until A is under A limit. Are you concerned that while
> performing writeback on A* that other tasks may push A1 over the A1
> limit? Such other task writers would also be calling
> mem_cgroup_balance_dirty_pages() later.
>
Hm, ok. Could you add comments to explain the algorithm ?
Thanks,
-Kame
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