Hi Shaohua,

On Wed, Mar 1, 2017 at 7:46 AM, Shaohua Li <s...@kernel.org> wrote:
> On Tue, Feb 28, 2017 at 11:41:43PM +0800, Ming Lei wrote:
>> The cost is 128bytes(8*16) stack space in kernel thread context, and
>> just use the bio helper to retrieve pages from bio.
>>
>> Signed-off-by: Ming Lei <tom.leim...@gmail.com>
>> ---
>>  drivers/md/raid10.c | 12 ++++++++++--
>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>> index 0b97631e3905..6ffb64ab45f8 100644
>> --- a/drivers/md/raid10.c
>> +++ b/drivers/md/raid10.c
>> @@ -4670,7 +4670,15 @@ static int handle_reshape_read_error(struct mddev 
>> *mddev,
>>       struct r10bio *r10b = &on_stack.r10_bio;
>>       int slot = 0;
>>       int idx = 0;
>> -     struct bio_vec *bvec = r10_bio->master_bio->bi_io_vec;
>> +     struct bio_vec *bvl;
>> +     struct page *pages[RESYNC_PAGES];
>> +
>> +     /*
>> +      * This bio is allocated in reshape_request(), and size
>> +      * is still RESYNC_PAGES
>> +      */
>> +     bio_for_each_segment_all(bvl, r10_bio->master_bio, idx)
>> +             pages[idx] = bvl->bv_page;
>
> The reshape bio is doing IO against the memory we allocated for r10_bio, I'm
> wondering why we can't get the pages from r10_bio. In this way, we don't need
> access the bio_vec any more.

Reshap read is special and the bio(r10_bio->master_bio) isn't allocated from
.r10buf_pool, please see reshape_request().

Thanks,
Ming Lei

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