Re: [PATCH V4 4/6] memcg: add per cgroup writeback pages accounting

[Michal Hocko <mhocko@suse.cz>]

On Sat 06-07-13 01:32:57, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@taobao.com>
> 
> Similar to dirty page, we add per cgroup writeback pages accounting. The lock
> rule still is:
>         mem_cgroup_begin_update_page_stat()
>         modify page WRITEBACK stat
>         mem_cgroup_update_page_stat()
>         mem_cgroup_end_update_page_stat()
> 
> There're two writeback interfaces to modify: test_{clear/set}_page_writeback().
> 
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> cc: Greg Thelen <gthelen@google.com>
> cc: Andrew Morton <akpm@linux-foundation.org>
> cc: Fengguang Wu <fengguang.wu@intel.com>
> cc: Mel Gorman <mgorman@suse.de>
> ---
>  include/linux/memcontrol.h |    1 +
>  mm/memcontrol.c            |    5 +++++
>  mm/page-writeback.c        |   15 +++++++++++++++
>  3 files changed, 21 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index f952be6..ccd35d8 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -43,6 +43,7 @@ enum mem_cgroup_stat_index {
>  	MEM_CGROUP_STAT_RSS_HUGE,	/* # of pages charged as anon huge */
>  	MEM_CGROUP_STAT_FILE_MAPPED,	/* # of pages charged as file rss */
>  	MEM_CGROUP_STAT_FILE_DIRTY,	/* # of dirty pages in page cache */
> +	MEM_CGROUP_STAT_WRITEBACK,	/* # of pages under writeback */
>  	MEM_CGROUP_STAT_SWAP,		/* # of pages, swapped out */
>  	MEM_CGROUP_STAT_NSTATS,
>  };
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1d31851..9126abc 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -92,6 +92,7 @@ static const char * const mem_cgroup_stat_names[] = {
>  	"mapped_file",
>  	"swap",
>  	"dirty",
> +	"writeback",

Ordering issue again (see mem_cgroup_stat_index)

>  };
>  
>  enum mem_cgroup_events_index {
[...]
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 3900e62..85de9a0 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2008,11 +2008,17 @@ EXPORT_SYMBOL(account_page_dirtied);
>  
>  /*
>   * Helper function for set_page_writeback family.
> + *
> + * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
> + * while modifying struct page state and accounting writeback pages.

I guess "while calling this function" would be sufficient

> + * See test_set_page_writeback for example.
> + *
>   * NOTE: Unlike account_page_dirtied this does not rely on being atomic
>   * wrt interrupts.
>   */
>  void account_page_writeback(struct page *page)
>  {
> +	mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
>  	inc_zone_page_state(page, NR_WRITEBACK);
>  }
>  EXPORT_SYMBOL(account_page_writeback);
[...]
-- 
Michal Hocko
SUSE Labs

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