# Re: \[RFC PATCH\] fs/direct-io.c: Set bi\_rw when alloc bio.

- From: Jeff Moyer \<hidden\>
- Date: 2012-07-30 13:31:37 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2012/07/66167
- Thread: https://ratatoskr.run/linux-fsdevel/2012/07/66167/t.md

```text
majianpeng [ref] writes:

> On 2012-07-27 22:21 Jeff Moyer [ref] Wrote:
>>majianpeng [ref] 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 <redacted>
>>
>>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 <redacted>
>>
> 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
```