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

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Message-ID: <5178D330.9030505@cn.fujitsu.com>
Date:	Thu, 25 Apr 2013 14:54:40 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	Jan Kara <jack@...e.cz>
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 04/24/2013 08:21 PM, Jan Kara wrote:

> 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?

Hi Jan,
   You are right, 'count' should not be greater than 'ocount' actually.
Please ignore this patch.

Thanks,
Gu

> 
> 								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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