From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 20 Oct 2017 06:51:10 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , Huang Ying , Andrew Morton , Alexander Viro , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-bcache@vger.kernel.org Subject: Re: [PATCH v3 07/49] bcache: comment on direct access to bvec table Message-ID: <20171019225109.GA27130@ming.t460p> References: <20170808084548.18963-1-ming.lei@redhat.com> <20170808084548.18963-8-ming.lei@redhat.com> <20170810112603.GD20308@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170810112603.GD20308@infradead.org> Sender: owner-linux-mm@kvack.org List-ID: 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org