[PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct_write()

[PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct_write()

[Gu Zheng]

>From 35947e6535d92c54cf523470cc8811e8b5fee3e5 Mon Sep 17 00:00:00 2001
From: Gu Zheng <guz.fnst@cn.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)'

Signed-off-by: Gu Zheng <guz.fnst@cn.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

Re: [PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct_write()

[Jan Kara]

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@cn.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@cn.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
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: [PATCH] mm/filemap.c: fix criteria of calling iov_shorten() in generic_file_direct_write()

[Gu Zheng]

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@cn.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@cn.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
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at  http://www.tux.org/lkml/