On Thu, Mar 2, 2017 at 3:47 PM, Shaohua Li <shli@xxxxxxxxxx> wrote: > On Thu, Mar 02, 2017 at 10:37:49AM +0800, Ming Lei wrote: >> Hi Shaohua, >> >> On Wed, Mar 1, 2017 at 7:46 AM, Shaohua Li <shli@xxxxxxxxxx> 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.leiming@xxxxxxxxx> >> >> --- >> >> 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(). > > Why does this matter? The bio is still doing IO to the memory allocated in > r10_bio. bi_private->r10_bio->the pages. Good question, :-) > > My guess why you think the reshape read is special is the bio->bi_private > doesn't pointer to resync_pages. And since you let resync_pages pointer to > r10_bio and not vice versa, we can't find r10_bio, correct? I think this is > another reason why r10_bio embeds resync_pages (I mean a pointer to > resync_pages). With this way I suggested, the reshape read isn't special at We still can get the resync_pages for r10_bio->master_bio via r10_bio->devs[0].bio in handle_reshape_read_error(), will do that in v3. > all. If we allocate memory for r10_bio/r1_bio, we shouldn't need access any bio > bvec. Right. Thanks, Ming Lei
