linux-kernel - Re: [PATCH V3 2/8] Make TestSetPageDirty and dirty page accounting in one func

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Message-ID: <20130102090803.GB22160@dhcp22.suse.cz>
Date:	Wed, 2 Jan 2013 10:08:03 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Sha Zhengju <handai.szj@...il.com>
Cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	dchinner@...hat.com, akpm@...ux-foundation.org,
	kamezawa.hiroyu@...fujitsu.com, gthelen@...gle.com,
	fengguang.wu@...el.com, glommer@...allels.com,
	Sha Zhengju <handai.szj@...bao.com>
Subject: Re: [PATCH V3 2/8] Make TestSetPageDirty and dirty page accounting
 in one func

On Wed 26-12-12 01:22:36, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@...bao.com>
> 
> Commit a8e7d49a(Fix race in create_empty_buffers() vs __set_page_dirty_buffers())
> extracts TestSetPageDirty from __set_page_dirty and is far away from
> account_page_dirtied. But it's better to make the two operations in one single
> function to keep modular. So in order to avoid the potential race mentioned in
> commit a8e7d49a, we can hold private_lock until __set_page_dirty completes.
> There's no deadlock between ->private_lock and ->tree_lock after confirmation.

Could you be more specific here? E.g. quote mm/filemap.c comment I have
mentioned during the first round of review?

> It's a prepare patch for following memcg dirty page accounting patches.
> 
> 
> Here is some test numbers that before/after this patch:
> Test steps(Mem-4g, ext4):
> drop_cache; sync
> fio (ioengine=sync/write/buffered/bs=4k/size=1g/numjobs=2/group_reporting/thread)

Could also add some rationale why you think this test is relevant?

> We test it for 10 times and get the average numbers:
> Before:
> write: io=2048.0MB, bw=254117KB/s, iops=63528.9 , runt=  8279msec
> lat (usec): min=1 , max=742361 , avg=30.918, stdev=1601.02
> After:
> write: io=2048.0MB, bw=254044KB/s, iops=63510.3 , runt=  8274.4msec
> lat (usec): min=1 , max=856333 , avg=31.043, stdev=1769.32
> 
> Note that the impact is little(<1%).
> 
> 
> Signed-off-by: Sha Zhengju <handai.szj@...bao.com>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>
> ---
>  fs/buffer.c |   24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index c017a2d..3b032b9 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -609,9 +609,15 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
>   * If warn is true, then emit a warning if the page is not uptodate and has
>   * not been truncated.
>   */
> -static void __set_page_dirty(struct page *page,
> +static int __set_page_dirty(struct page *page,
>  		struct address_space *mapping, int warn)
>  {
> +	if (unlikely(!mapping))
> +		return !TestSetPageDirty(page);
> +
> +	if (TestSetPageDirty(page))
> +		return 0;
> +
>  	spin_lock_irq(&mapping->tree_lock);
>  	if (page->mapping) {	/* Race with truncate? */
>  		WARN_ON_ONCE(warn && !PageUptodate(page));
> @@ -621,6 +627,8 @@ static void __set_page_dirty(struct page *page,
>  	}
>  	spin_unlock_irq(&mapping->tree_lock);
>  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> +	return 1;
>  }
>  
>  /*
> @@ -666,11 +674,9 @@ int __set_page_dirty_buffers(struct page *page)
>  			bh = bh->b_this_page;
>  		} while (bh != head);
>  	}
> -	newly_dirty = !TestSetPageDirty(page);
> +	newly_dirty = __set_page_dirty(page, mapping, 1);
>  	spin_unlock(&mapping->private_lock);
>  
> -	if (newly_dirty)
> -		__set_page_dirty(page, mapping, 1);
>  	return newly_dirty;
>  }
>  EXPORT_SYMBOL(__set_page_dirty_buffers);
> @@ -1125,14 +1131,8 @@ void mark_buffer_dirty(struct buffer_head *bh)
>  			return;
>  	}
>  
> -	if (!test_set_buffer_dirty(bh)) {
> -		struct page *page = bh->b_page;
> -		if (!TestSetPageDirty(page)) {
> -			struct address_space *mapping = page_mapping(page);
> -			if (mapping)
> -				__set_page_dirty(page, mapping, 0);
> -		}
> -	}
> +	if (!test_set_buffer_dirty(bh))
> +		__set_page_dirty(bh->b_page, page_mapping(bh->b_page), 0);
>  }
>  EXPORT_SYMBOL(mark_buffer_dirty);
>  
> -- 
> 1.7.9.5
> 

-- 
Michal Hocko
SUSE Labs
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