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. 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 all. If we allocate memory for r10_bio/r1_bio, we shouldn't need access any bio bvec. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
