Re: [PATCH V5 5/8] memcg: add per cgroup writeback pages accounting

From: Greg Thelen <gthelen@google.com>
To: Sha Zhengju <handai.szj@gmail.com>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	cgroups@vger.kernel.org, mhocko@suse.cz,
	kamezawa.hiroyu@jp.fujitsu.com, glommer@gmail.com,
	fengguang.wu@intel.com, akpm@linux-foundation.org,
	Sha Zhengju <handai.szj@taobao.com>
Subject: Re: [PATCH V5 5/8] memcg: add per cgroup writeback pages accounting
Date: Sun, 04 Aug 2013 11:51:27 -0700	[thread overview]
Message-ID: <xr93zjsxuw5s.fsf@gthelen.mtv.corp.google.com> (raw)
In-Reply-To: 1375358051-10306-1-git-send-email-handai.szj@taobao.com

On Thu, Aug 01 2013, 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().
> Lock order:
> 	--> memcg->move_lock
> 	  --> mapping->tree_lock
>
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> ---
>  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 8f3e514..6c18a6d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -91,6 +91,7 @@ static const char * const mem_cgroup_stat_names[] = {
>  	"rss_huge",
>  	"mapped_file",
>  	"dirty",
> +	"writeback",
>  	"swap",
>  };
>  
> @@ -3812,6 +3813,10 @@ static int mem_cgroup_move_account(struct page *page,
>  		mem_cgroup_move_account_page_stat(from, to, nr_pages,
>  			MEM_CGROUP_STAT_FILE_DIRTY);
>  
> +	if (PageWriteback(page))
> +		mem_cgroup_move_account_page_stat(from, to, nr_pages,
> +			MEM_CGROUP_STAT_WRITEBACK);
> +
>  	mem_cgroup_charge_statistics(from, page, anon, -nr_pages);
>  
>  	/* caller should have done css_get */
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index a09f518..2fa6a52 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 calling this function.
> + * 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);
> @@ -2243,7 +2249,10 @@ int test_clear_page_writeback(struct page *page)
>  {
>  	struct address_space *mapping = page_mapping(page);
>  	int ret;
> +	bool locked;
> +	unsigned long memcg_flags;
>  
> +	mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
>  	if (mapping) {
>  		struct backing_dev_info *bdi = mapping->backing_dev_info;
>  		unsigned long flags;
> @@ -2264,9 +2273,11 @@ int test_clear_page_writeback(struct page *page)
>  		ret = TestClearPageWriteback(page);
>  	}
>  	if (ret) {
> +		mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
>  		dec_zone_page_state(page, NR_WRITEBACK);
>  		inc_zone_page_state(page, NR_WRITTEN);
>  	}
> +	mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
>  	return ret;
>  }
>  
> @@ -2274,7 +2285,10 @@ int test_set_page_writeback(struct page *page)
>  {
>  	struct address_space *mapping = page_mapping(page);
>  	int ret;
> +	bool locked;
> +	unsigned long flags;

I recommend using memcg_flags here, which matches the pattern in
account_page_writeback, to avoid overlapping the nested 'flags' variable
below.

Otherwise,
Reviewed-by: Greg Thelen <gthelen@google.com>

>  
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>  	if (mapping) {
>  		struct backing_dev_info *bdi = mapping->backing_dev_info;
>  		unsigned long flags;
> @@ -2301,6 +2315,7 @@ 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;
>  
>  }