lkml.org 
[lkml]   [2011]   [Jun]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v8 10/12] memcg: create support routines for page-writeback
On Fri,  3 Jun 2011 09:12:16 -0700
Greg Thelen <gthelen@google.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@google.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


> + /*
> + * keep throttling and writing inode data so long as mem is over
> + * its dirty limit.
> + */
> + for (shared_inodes = false; ; ) {
> + struct writeback_control wbc = {
> + .sync_mode = WB_SYNC_NONE,
> + .older_than_this = NULL,
> + .range_cyclic = 1,
> + .for_cgroup = 1,
> + .nr_to_write = write_chunk,
> + .shared_inodes = shared_inodes,
> + };
> +
> + /*
> + * if mem is under dirty limit, then break from
> + * throttling loop.
> + */
> + mem_cgroup_dirty_info(sys_available_mem, mem, &info);
> + nr_reclaimable = dirty_info_reclaimable(&info);
> + over = nr_reclaimable > info.dirty_thresh;
> + trace_mem_cgroup_consider_fg_writeback(
> + id, bdi, nr_reclaimable, info.dirty_thresh,
> + over);
> + if (!over)
> + break;
> +
> + mem_cgroup_mark_over_bg_thresh(mem);
> + writeback_inodes_wb(&bdi->wb, &wbc);
> + trace_mem_cgroup_fg_writeback(write_chunk, &wbc);
> + /* if no progress, then consider shared inodes */
> + if ((wbc.nr_to_write == write_chunk) &&
> + !shared_inodes) {
> + trace_mem_cgroup_enable_shared_writeback(id);
> + shared_inodes = true;
> + }
> +
> + /*
> + * Sleep up to 100ms to throttle writer and wait for
> + * queued background I/O to complete.
> + */
> + __set_current_state(TASK_UNINTERRUPTIBLE);
> + io_schedule_timeout(pause);
> + pause <<= 1;
> + if (pause > HZ / 10)
> + pause = HZ / 10;

Hmm, is this exponential back off "pause" is from mm/page-writeback.c ?
I'm happy if we can have a shared code. (But ok if it adds some messy.)



> + }
> +
> + /* if mem is over background limit, then queue bg writeback */
> + over = nr_reclaimable >= info.background_thresh;
> + trace_mem_cgroup_consider_bg_writeback(
> + id, bdi, nr_reclaimable, info.background_thresh,
> + over);
> + if (over)
> + mem_cgroup_queue_bg_writeback(mem, bdi);
> + }
> +
> + if (ref_mem)
> + css_put(&ref_mem->css);
> +}
> +
> +/*
> + * Return the dirty thresholds and usage for the mem (within the ancestral chain
> + * of @mem) closest to its dirty limit or the first memcg over its limit.
> + *
> + * The check is not stable because the usage and limits can change asynchronous
> + * to this routine.
> + */
> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
> + struct mem_cgroup *mem,
> + struct dirty_info *info)
> +{
> + unsigned long usage;
> + struct dirty_info uninitialized_var(cur_info);
> +
> + if (mem_cgroup_disabled())
> + return false;
> +
> + info->nr_writeback = ULONG_MAX; /* invalid initial value */
> +
> + /* walk up hierarchy enabled parents */
> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) {
> + mem_cgroup_dirty_info(sys_available_mem, mem, &cur_info);
> + usage = dirty_info_reclaimable(&cur_info) +
> + cur_info.nr_writeback;
> +
> + /* if over limit, stop searching */
> + if (usage >= cur_info.dirty_thresh) {
> + *info = cur_info;
> + break;
> + }
> +
> + /*
> + * Save dirty usage of mem closest to its limit if either:
> + * - mem is the first mem considered
> + * - mem dirty margin is smaller than last recorded one
> + */
> + if ((info->nr_writeback == ULONG_MAX) ||
> + (cur_info.dirty_thresh - usage) <
> + (info->dirty_thresh -
> + (dirty_info_reclaimable(info) + info->nr_writeback)))
> + *info = cur_info;
> + }
> +
> + return info->nr_writeback != ULONG_MAX;
> +}
> +
> static void mem_cgroup_start_move(struct mem_cgroup *mem)
> {
> int cpu;
> --
> 1.7.3.1
>



\
 
 \ /
  Last update: 2011-06-07 11:01    [from the cache]
©2003-2011 Jasper Spaans