Messages in this thread | | | Date | Fri, 20 Oct 2017 06:51:10 +0800 | From | Ming Lei <> | Subject | Re: [PATCH v3 07/49] bcache: comment on direct access to bvec table |
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On Thu, Aug 10, 2017 at 04:26:03AM -0700, Christoph Hellwig wrote: > I think all this bcache code needs bigger attention. For one > bio_alloc_pages is only used in bcache, so we should move it in there.
Looks a good idea.
> > Second the way bio_alloc_pages is currently written looks potentially > dangerous for multi-page biovecs, so we should think about a better > calling convention. The way bcache seems to generally use it is by > allocating a bio, then calling bch_bio_map on it and then calling > bio_alloc_pages. I think it just needs a new bio_alloc_pages calling > convention that passes the size to be allocated and stop looking into > the segment count.
Looks a good idea, will try to do in this way.
> > Second bch_bio_map isn't something we should be doing in a driver, > it should be rewritten using bio_add_page.
Yes, the idea way is to use bio_add_page always, but given bch_bio_map() is used on a fresh bio, it is safe, and this work can be done in another bcache cleanup patch.
> > > diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c > > index 866dcf78ff8e..3da595ae565b 100644 > > --- a/drivers/md/bcache/btree.c > > +++ b/drivers/md/bcache/btree.c > > @@ -431,6 +431,7 @@ static void do_btree_node_write(struct btree *b) > > > > continue_at(cl, btree_node_write_done, NULL); > > } else { > > + /* No harm for multipage bvec since the new is just allocated */ > > b->bio->bi_vcnt = 0; > > This should go away - bio_alloc_pages or it's replacement should not > modify bi_vcnt on failure.
OK.
> > > + /* single page bio, safe for multipage bvec */ > > dc->sb_bio.bi_io_vec[0].bv_page = sb_page; > > needs to use bio_add_page.
OK.
> > > + /* single page bio, safe for multipage bvec */ > > ca->sb_bio.bi_io_vec[0].bv_page = sb_page; > > needs to use bio_add_page.
OK.
-- Ming
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