Re: [PATCH 6/7] memcg: add per cgroup writeback pages accounting

[Greg Thelen <gthelen@google.com>]

On Thu, Jun 28 2012, 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 interface to modify: test_clear/set_page_writeback.
>
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> ---
>  include/linux/memcontrol.h |    1 +
>  mm/memcontrol.c            |    5 +++++
>  mm/page-writeback.c        |   12 ++++++++++++
>  3 files changed, 18 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index ad37b59..9193d93 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -39,6 +39,7 @@ enum mem_cgroup_stat_index {
>  	MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
>  	MEM_CGROUP_STAT_SWAP, /* # of pages, swapped out */
>  	MEM_CGROUP_STAT_FILE_DIRTY,  /* # of dirty pages in page cache */
> +	MEM_CGROUP_STAT_FILE_WRITEBACK,  /* # of pages under writeback */
>  	MEM_CGROUP_STAT_NSTATS,
>  };
>  
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 90e2946..8493119 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -83,6 +83,7 @@ static const char * const mem_cgroup_stat_names[] = {
>  	"mapped_file",
>  	"swap",
>  	"dirty",
> +	"writeback",
>  };
>  
>  enum mem_cgroup_events_index {
> @@ -2604,6 +2605,10 @@ static int mem_cgroup_move_account(struct page *page,
>  		mem_cgroup_move_account_page_stat(from, to,
>  				MEM_CGROUP_STAT_FILE_DIRTY);
>  
> +	if (PageWriteback(page))
> +		mem_cgroup_move_account_page_stat(from, to,
> +				MEM_CGROUP_STAT_FILE_WRITEBACK);
> +
>  	mem_cgroup_charge_statistics(from, anon, -nr_pages);
>  
>  	/* caller should have done css_get */
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index e79a2f7..7398836 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1981,6 +1981,7 @@ EXPORT_SYMBOL(account_page_dirtied);
>   */
>  void account_page_writeback(struct page *page)
>  {
> +	mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_WRITEBACK);

As already mentioned, I'd also like to see a comment added to
account_page_writeback() describing the new locking requirements
(specifically mem_cgroup_begin_update_page_stat being held by caller).

>  	inc_zone_page_state(page, NR_WRITEBACK);
>  }
>  EXPORT_SYMBOL(account_page_writeback);
> @@ -2214,7 +2215,10 @@ int test_clear_page_writeback(struct page *page)
>  {
>  	struct address_space *mapping = page_mapping(page);
>  	int ret;
> +	bool locked;
> +	unsigned long flags;
>  
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>  	if (mapping) {
>  		struct backing_dev_info *bdi = mapping->backing_dev_info;
>  		unsigned long flags;
> @@ -2235,9 +2239,12 @@ int test_clear_page_writeback(struct page *page)
>  		ret = TestClearPageWriteback(page);
>  	}
>  	if (ret) {
> +		mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_WRITEBACK);
>  		dec_zone_page_state(page, NR_WRITEBACK);
>  		inc_zone_page_state(page, NR_WRITTEN);
>  	}
> +
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
>  	return ret;
>  }
>  
> @@ -2245,7 +2252,10 @@ int test_set_page_writeback(struct page *page)
>  {
>  	struct address_space *mapping = page_mapping(page);
>  	int ret;
> +	bool locked;
> +	unsigned long flags;
>  
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>  	if (mapping) {
>  		struct backing_dev_info *bdi = mapping->backing_dev_info;
>  		unsigned long flags;
> @@ -2272,6 +2282,8 @@ int test_set_page_writeback(struct page *page)
>  	}
>  	if (!ret)
>  		account_page_writeback(page);
> +
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
>  	return ret;
>  
>  }

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