2011-06-09 (ë), 12:21 +1000, NeilBrown:
> On Thu, 9 Jun 2011 03:04:33 +0900 Namhyung Kim <namhyung@xxxxxxxxx> wrote:
>
> > When performing a recovery, only first 2 slots in r10_bio are in use,
> > for read and write respectively. However all of pages in the write bio
> > are never used and just replaced to read bio's when the read completes.
> >
> > Get rid of those unused pages and share read pages properly.
> >
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxx>
> > ---
> > drivers/md/raid10.c | 13 ++++++++++---
> > 1 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index a53779ffdf89..621594981339 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -116,6 +116,13 @@ static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
> > goto out_free_bio;
> > r10_bio->devs[j].bio = bio;
> > }
> > +
> > + /*
> > + * We can share bv_page's during the recovery
> > + */
> > + if (!test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery))
> > + nalloc--;
> > +
> > /*
> > * Allocate RESYNC_PAGES data pages and attach them
> > * where needed.
> > @@ -1363,16 +1370,16 @@ static void recovery_request_write(mddev_t *mddev, r10bio_t *r10_bio)
> > int i, d;
> > struct bio *bio, *wbio;
> >
> > -
> > - /* move the pages across to the second bio
> > + /*
> > + * share the pages with the first bio
> > * and submit the write request
> > */
> > bio = r10_bio->devs[0].bio;
> > wbio = r10_bio->devs[1].bio;
> > for (i=0; i < wbio->bi_vcnt; i++) {
> > struct page *p = bio->bi_io_vec[i].bv_page;
> > - bio->bi_io_vec[i].bv_page = wbio->bi_io_vec[i].bv_page;
> > wbio->bi_io_vec[i].bv_page = p;
> > + get_page(p);
> > }
> > d = r10_bio->devs[1].devnum;
> >
>
>
> Thanks. Interesting idea, but I don't think this code is safe.
>
> We end up calling bio_add_page on with an uninitialised 'page' (in
> sync_request()). This could result on BIOVEC_PHYS_MERGEABLE doing funny
> things.
>
Arrrh, right. I missed that part.
> It would be OK to set up the two links to the one page in r10buf_pool_alloc,
> so recovery_request_write doesn't need to do anything with pages.
> That would probably be even more safe than the current code.
>
Agreed, will resend v2. Thanks for the review.
--
Regards,
Namhyung Kim
--
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
