[RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

[RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

[majianpeng]

When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
it will use bi_rw.
Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
>> if ((bvm->bi_rw & 1) == WRITE)
>>		return biovec->bv_len; /* always allow writes to be mergeable */

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>

There are many place like this in kernel.If you think this patch ok, i will correct those.
---
 fs/direct-io.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 1faf4cb..77f0bbf 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 
 	bio->bi_bdev = bdev;
 	bio->bi_sector = first_sector;
+	bio->bi_rw = dio->rw;
 	if (dio->is_async)
 		bio->bi_end_io = dio_bio_end_aio;
 	else
-- 
1.7.5.4

Re: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

[Jeff Moyer]

majianpeng <majianpeng@gmail.com> writes:

> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
> it will use bi_rw.
> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
>>> if ((bvm->bi_rw & 1) == WRITE)
>>>		return biovec->bv_len; /* always allow writes to be mergeable */
>
> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>

Good catch.  How did you find this?  Did you experience data corruption
as a result of this oversight, reduced performance due to missed merge
opportunities, or did you just notice it in reviewing the code?

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

>
> There are many place like this in kernel.If you think this patch ok, i will correct those.
> ---
>  fs/direct-io.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 1faf4cb..77f0bbf 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
>  
>  	bio->bi_bdev = bdev;
>  	bio->bi_sector = first_sector;
> +	bio->bi_rw = dio->rw;
>  	if (dio->is_async)
>  		bio->bi_end_io = dio_bio_end_aio;
>  	else

Re: Re: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

[majianpeng]

On 2012-07-27 22:21 Jeff Moyer <jmoyer@redhat.com> Wrote:
>majianpeng <majianpeng@gmail.com> writes:
>
>> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
>> it will use bi_rw.
>> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
>> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
>>>> if ((bvm->bi_rw & 1) == WRITE)
>>>>		return biovec->bv_len; /* always allow writes to be mergeable */
>>
>> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
>
>Good catch.  How did you find this?  Did you experience data corruption
>as a result of this oversight, reduced performance due to missed merge
>opportunities, or did you just notice it in reviewing the code?
>
>Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
>
Sorry for late to reply. When i analysed the performance of raid5, i found this bug.

>>
>> There are many place like this in kernel.If you think this patch ok, i will correct those.
>> ---
>>  fs/direct-io.c |    1 +
>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/direct-io.c b/fs/direct-io.c
>> index 1faf4cb..77f0bbf 100644
>> --- a/fs/direct-io.c
>> +++ b/fs/direct-io.c
>> @@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
>>  
>>  	bio->bi_bdev = bdev;
>>  	bio->bi_sector = first_sector;
>> +	bio->bi_rw = dio->rw;
>>  	if (dio->is_async)
>>  		bio->bi_end_io = dio_bio_end_aio;
>>  	else

Re: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

[Jeff Moyer]

majianpeng <majianpeng@gmail.com> writes:

> On 2012-07-27 22:21 Jeff Moyer <jmoyer@redhat.com> Wrote:
>>majianpeng <majianpeng@gmail.com> writes:
>>
>>> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
>>> it will use bi_rw.
>>> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
>>> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
>>>>> if ((bvm->bi_rw & 1) == WRITE)
>>>>>		return biovec->bv_len; /* always allow writes to be mergeable */
>>>
>>> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
>>
>>Good catch.  How did you find this?  Did you experience data corruption
>>as a result of this oversight, reduced performance due to missed merge
>>opportunities, or did you just notice it in reviewing the code?
>>
>>Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
>>
> Sorry for late to reply. When i analysed the performance of raid5, i found this bug.

OK, thanks.  In the future, it would be good to include that information
in the patch description.

Cheers,
Jeff