From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: [PATCH 03/12] block: bio_release_pages: use flags arg instead of bool Date: Tue, 30 Jul 2019 11:57:02 -0400 Message-ID: <20190730155702.GB10366@redhat.com> References: <20190724042518.14363-1-jhubbard@nvidia.com> <20190724042518.14363-4-jhubbard@nvidia.com> <20190724053053.GA18330@infradead.org> <20190729205721.GB3760@redhat.com> <20190730102557.GA1700@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20190730102557.GA1700@lst.de> Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig Cc: Christoph Hellwig , john.hubbard@gmail.com, Andrew Morton , Alexander Viro , Anna Schumaker , "David S . Miller" , Dominique Martinet , Eric Van Hensbergen , Jason Gunthorpe , Jason Wang , Jens Axboe , Latchesar Ionkov , "Michael S . Tsirkin" , Miklos Szeredi , Trond Myklebust , Matthew Wilcox , linux-mm@kvack.org, LKML , ceph-devel@vger.kernel.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-cifs@vger. List-Id: ceph-devel.vger.kernel.org On Tue, Jul 30, 2019 at 12:25:57PM +0200, Christoph Hellwig wrote: > On Mon, Jul 29, 2019 at 04:57:21PM -0400, Jerome Glisse wrote: > > > All pages releases by bio_release_pages should come from > > > get_get_user_pages, so I don't really see the point here. > > > > No they do not all comes from GUP for see various callers > > of bio_check_pages_dirty() for instance iomap_dio_zero() > > > > I have carefully tracked down all this and i did not do > > anyconvertion just for the fun of it :) > > Well, the point is _should_ not necessarily do. iomap_dio_zero adds the > ZERO_PAGE, which we by definition don't need to refcount. So we can > mark this bio BIO_NO_PAGE_REF safely after removing the get_page there. > > Note that the equivalent in the old direct I/O code, dio_refill_pages, > will be a little more complicated as it can match user pages and the > ZERO_PAGE in a single bio, so a per-bio flag won't handle it easily. > Maybe we just need to use a separate bio there as well. > > In general with series like this we should not encode the status quo an > pile new hacks upon the old one, but thing where we should be and fix > up the old warts while having to wade through all that code. Other user can also add page that are not coming from GUP but need to have a reference see __blkdev_direct_IO() saddly bio get fill from many different places and not always with GUP. So we can not say that all pages here are coming from bio. I had a different version of the patchset i think that was adding a new release dirty function for GUP versus non GUP bio. I posted it a while ago, i will try to dig it up once i am back. Cheers, Jérôme