Re: [PATCH V2 4/6] memcg: add per cgroup dirty pages accounting

[Greg Thelen <gthelen@google.com>]

On Fri, Jul 27 2012, Sha Zhengju wrote:

> From: Sha Zhengju <handai.szj@taobao.com>
>
> This patch adds memcg routines to count dirty pages, which allows memory controller
> to maintain an accurate view of the amount of its dirty memory and can provide some
> info for users while group's direct reclaim is working.
>
> After Kame's commit 89c06bd5(memcg: use new logic for page stat accounting), we can
> use 'struct page' flag to test page state instead of per page_cgroup flag. But memcg
> has a feature to move a page from a cgroup to another one and may have race between
> "move" and "page stat accounting". So in order to avoid the race we have designed a
> bigger lock:
>
>          mem_cgroup_begin_update_page_stat()
>          modify page information        -->(a)
>          mem_cgroup_update_page_stat()  -->(b)
>          mem_cgroup_end_update_page_stat()
>
> It requires (a) and (b)(dirty pages accounting) can stay close enough.
>
> In the previous two prepare patches, we have reworked the vfs set page dirty routines
> and now the interfaces are more explicit:
>         incrementing (2):
>                 __set_page_dirty
>                 __set_page_dirty_nobuffers
>         decrementing (2):
>                 clear_page_dirty_for_io
>                 cancel_dirty_page
>
>
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujtisu.com>
> Acked-by: Fengguang Wu <fengguang.wu@intel.com>
> ---
>  fs/buffer.c                |   16 +++++++++++++---
>  include/linux/memcontrol.h |    1 +
>  mm/filemap.c               |    9 +++++++++
>  mm/memcontrol.c            |   28 +++++++++++++++++++++-------
>  mm/page-writeback.c        |   31 ++++++++++++++++++++++++++-----
>  mm/truncate.c              |    6 ++++++
>  6 files changed, 76 insertions(+), 15 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index ffcfb87..e7b5766 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -613,11 +613,19 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
>  int __set_page_dirty(struct page *page,
>  		struct address_space *mapping, int warn)
>  {
> +	bool locked;
> +	unsigned long flags;
> +	int ret = 1;
> +
>  	if (unlikely(!mapping))
>  		return !TestSetPageDirty(page);
>  
> -	if (TestSetPageDirty(page))
> -		return 0;
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> +
> +	if (TestSetPageDirty(page)) {
> +		ret = 0;
> +		goto out;
> +	}
>  
>  	spin_lock_irq(&mapping->tree_lock);

There are two problems here:
1. Here we grab mem_cgroup_begin_update_page_stat() lock(s) and then
   tree_lock (this can cause AB/BA deadlock - more below)
2. Here we grab the tree_lock with spin_lock_irq(), which assumes that
   interrupts are not already disabled by spin_lock_irq[save]()..  But
   mem_cgroup_begin_update_page_stat() may disable interrupts.  One
   solution would be to convert this spin_lock_irq to spin_lock_irqsave
   with a second flags local variable.

>  	if (page->mapping) {	/* Race with truncate? */
> @@ -629,7 +637,9 @@ int __set_page_dirty(struct page *page,
>  	spin_unlock_irq(&mapping->tree_lock);
>  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>  
> -	return 1;
> +out:
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
> +	return ret;
>  }
>  EXPORT_SYMBOL(__set_page_dirty);
>  
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index c1e2617..8c6b8ca 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -41,6 +41,7 @@ enum mem_cgroup_stat_index {
>  	MEM_CGROUP_STAT_RSS,	   /* # of pages charged as anon rss */
>  	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_NSTATS,
>  };
>  
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a4a5260..7f53fb0 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -62,6 +62,10 @@
>   *      ->swap_lock		(exclusive_swap_page, others)
>   *        ->mapping->tree_lock
>   *
> + *    ->private_lock		(__set_page_dirty_buffers)
> + *      ->memcg->move_lock	(mem_cgroup_begin_update_page_stat->move_lock_mem_cgroup)
> + *        ->mapping->tree_lock
> + *
>   *  ->i_mutex
>   *    ->i_mmap_mutex		(truncate->unmap_mapping_range)
>   *
> @@ -112,6 +116,8 @@
>  void __delete_from_page_cache(struct page *page)
>  {
>  	struct address_space *mapping = page->mapping;
> +	bool locked;
> +	unsigned long flags;
>  
>  	/*
>  	 * if we're uptodate, flush out into the cleancache, otherwise
> @@ -139,10 +145,13 @@ void __delete_from_page_cache(struct page *page)
>  	 * Fix it up by doing a final dirty accounting check after
>  	 * having removed the page entirely.
>  	 */
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);

Here caller of __delete_from_page_cache() already holds tree_lock and we
grab mem_cgroup_begin_update_page_stat() lock(s).

This can cause an AB/BA deadlock.  We need to be consistent with lock
ordering.  The filemap.c lock ordering comment indicates that tree_lock
should be grabbed after the mem_cgroup_begin_update_page_stat() lock(s).

>  	if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
> +		mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
>  		dec_zone_page_state(page, NR_FILE_DIRTY);
>  		dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
>  	}
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
>  }
>  
>  /**
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index aef9fb0..cdcd547 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -85,6 +85,7 @@ static const char * const mem_cgroup_stat_names[] = {
>  	"rss",
>  	"mapped_file",
>  	"swap",
> +	"dirty",
>  };
>  
>  enum mem_cgroup_events_index {
> @@ -2541,6 +2542,18 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>  }
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  
> +static inline
> +void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
> +					struct mem_cgroup *to,
> +					enum mem_cgroup_stat_index idx)
> +{
> +	/* Update stat data for mem_cgroup */
> +	preempt_disable();
> +	__this_cpu_dec(from->stat->count[idx]);
> +	__this_cpu_inc(to->stat->count[idx]);
> +	preempt_enable();
> +}
> +
>  /**
>   * mem_cgroup_move_account - move account of the page
>   * @page: the page
> @@ -2586,13 +2599,14 @@ static int mem_cgroup_move_account(struct page *page,
>  
>  	move_lock_mem_cgroup(from, &flags);
>  
> -	if (!anon && page_mapped(page)) {
> -		/* Update mapped_file data for mem_cgroup */
> -		preempt_disable();
> -		__this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> -		__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
> -		preempt_enable();
> -	}
> +	if (!anon && page_mapped(page))
> +		mem_cgroup_move_account_page_stat(from, to,
> +				MEM_CGROUP_STAT_FILE_MAPPED);
> +
> +	if (PageDirty(page))
> +		mem_cgroup_move_account_page_stat(from, to,
> +				MEM_CGROUP_STAT_FILE_DIRTY);
> +
>  	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 93d8d2f..233e7ac 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1932,11 +1932,17 @@ int __set_page_dirty_no_writeback(struct page *page)
>  
>  /*
>   * Helper function for set_page_dirty family.
> + *
> + * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
> + * while modifying struct page state and accounting dirty pages.
> + * See __set_page_dirty for example.
> + *
>   * NOTE: This relies on being atomic wrt interrupts.
>   */
>  void account_page_dirtied(struct page *page, struct address_space *mapping)
>  {
>  	if (mapping_cap_account_dirty(mapping)) {
> +		mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
>  		__inc_zone_page_state(page, NR_FILE_DIRTY);
>  		__inc_zone_page_state(page, NR_DIRTIED);
>  		__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
> @@ -1976,12 +1982,19 @@ EXPORT_SYMBOL(account_page_writeback);
>   */
>  int __set_page_dirty_nobuffers(struct page *page)
>  {
> +	bool locked;
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> +
>  	if (!TestSetPageDirty(page)) {
>  		struct address_space *mapping = page_mapping(page);
>  		struct address_space *mapping2;
>  
> +		ret = 1;
>  		if (!mapping)
> -			return 1;
> +			goto out;
>  
>  		spin_lock_irq(&mapping->tree_lock);
>  		mapping2 = page_mapping(page);
> @@ -1997,9 +2010,11 @@ int __set_page_dirty_nobuffers(struct page *page)
>  			/* !PageAnon && !swapper_space */
>  			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
>  		}
> -		return 1;
>  	}
> -	return 0;
> +
> +out:
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
> +	return ret;
>  }
>  EXPORT_SYMBOL(__set_page_dirty_nobuffers);
>  
> @@ -2114,6 +2129,9 @@ EXPORT_SYMBOL(set_page_dirty_lock);
>  int clear_page_dirty_for_io(struct page *page)
>  {
>  	struct address_space *mapping = page_mapping(page);
> +	bool locked;
> +	unsigned long flags;
> +	int ret = 0;
>  
>  	BUG_ON(!PageLocked(page));
>  
> @@ -2155,13 +2173,16 @@ int clear_page_dirty_for_io(struct page *page)
>  		 * the desired exclusion. See mm/memory.c:do_wp_page()
>  		 * for more comments.
>  		 */
> +		mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>  		if (TestClearPageDirty(page)) {
> +			mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
>  			dec_zone_page_state(page, NR_FILE_DIRTY);
>  			dec_bdi_stat(mapping->backing_dev_info,
>  					BDI_RECLAIMABLE);
> -			return 1;
> +			ret = 1;
>  		}
> -		return 0;
> +		mem_cgroup_end_update_page_stat(page, &locked, &flags);
> +		return ret;
>  	}
>  	return TestClearPageDirty(page);
>  }
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 75801ac..052016a 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -73,9 +73,14 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
>   */
>  void cancel_dirty_page(struct page *page, unsigned int account_size)
>  {
> +	bool locked;
> +	unsigned long flags;
> +
> +	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>  	if (TestClearPageDirty(page)) {
>  		struct address_space *mapping = page->mapping;
>  		if (mapping && mapping_cap_account_dirty(mapping)) {
> +			mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
>  			dec_zone_page_state(page, NR_FILE_DIRTY);
>  			dec_bdi_stat(mapping->backing_dev_info,
>  					BDI_RECLAIMABLE);
> @@ -83,6 +88,7 @@ void cancel_dirty_page(struct page *page, unsigned int account_size)
>  				task_io_account_cancelled_write(account_size);
>  		}
>  	}
> +	mem_cgroup_end_update_page_stat(page, &locked, &flags);
>  }
>  EXPORT_SYMBOL(cancel_dirty_page);

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