linux-kernel - Re: [PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct

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Date:	Wed, 24 Apr 2013 14:21:00 +0200
From:	Jan Kara <jack@...e.cz>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>, Jens <axboe@...nel.dk>
Subject: Re: [PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in
 generic_file_direct_write()

On Tue 23-04-13 16:37:43, Gu Zheng wrote:
> From 35947e6535d92c54cf523470cc8811e8b5fee3e5 Mon Sep 17 00:00:00 2001
> From: Gu Zheng <guz.fnst@...fujitsu.com>
> Date: Tue, 23 Apr 2013 16:09:04 +0800
> Subject: [PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct_write()
> 
> generic_file_direct_write() compares 'count'(the max count we actually can write)
> with 'ocount'(the count we request to write) to see if there is need to call
> iov_shorten() to reduce number of segments and the iovec's length. If the
> 'count' is equal or greater than 'ocount', there is no need to call iov_shorten()
> indeed. So the judgement should be changed:
> 'if (count != ocount)' --> 'if (count < ocount)'
  Thanks for the patch but it shouldn't be really possible that count >
ocount, should it? So your patch doesn't really fix anything. Or am I
missing something?

								Honza
> 
> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> ---
>  mm/filemap.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index e1979fd..c566b9c 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2183,7 +2183,7 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
>  	size_t		write_len;
>  	pgoff_t		end;
>  
> -	if (count != ocount)
> +	if (count < ocount)
>  		*nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
>  
>  	write_len = iov_length(iov, *nr_segs);
> -- 
> 1.7.7
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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