linux-kernel - Re: [RESEND PATCH] fs/buffer.c: exit if already confirmed page has dirty and writeback buffers

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Message-ID: <20131107114459.GB31798@quack.suse.cz>
Date:	Thu, 7 Nov 2013 12:44:59 +0100
From:	Jan Kara <jack@...e.cz>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH] fs/buffer.c: exit if already confirmed page has
 dirty and writeback buffers

On Tue 05-11-13 18:02:03, Gu Zheng wrote:
> Stop the loop of iterating bh if we have confirmed page
> has dirty and writeback buffers.
  Thanks for the patch. What I'm somewhat missing here is a motivation of
the patch. For the common case where blocksize == pagesize this is a noop
(only adds some code). For the case where blocksize < pagesize we can
possibly save checking some buffers but how common is that going be? Does
that minimal speed up outweight the cost of additional check / code
complication?

								Honza

> 
> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> ---
>  fs/buffer.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 6024877..519cc5c 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -112,7 +112,7 @@ void buffer_check_dirty_writeback(struct page *page,
>  			*dirty = true;
>  
>  		bh = bh->b_this_page;
> -	} while (bh != head);
> +	} while ((bh != head) && !(*writeback && *dirty));
>  }
>  EXPORT_SYMBOL(buffer_check_dirty_writeback);
>  
> -- 
> 1.7.7
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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