From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sat, 8 Dec 2018 10:12:58 -0800 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , =?iso-8859-1?B?Suly9G1l?= Glisse , John Hubbard , Matthew Wilcox , John Hubbard , Andrew Morton , Linux MM , Jan Kara , tom@talpey.com, Al Viro , benve@cisco.com, Christopher Lameter , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , Mike Marciniszyn , rcampbell@nvidia.com, Linux Kernel Mailing List , linux-fsdevel Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions Message-ID: <20181208181258.GA13075@infradead.org> References: <20181205011519.GV10377@bombadil.infradead.org> <20181205014441.GA3045@redhat.com> <59ca5c4b-fd5b-1fc6-f891-c7986d91908e@nvidia.com> <7b4733be-13d3-c790-ff1b-ac51b505e9a6@nvidia.com> <20181207191620.GD3293@redhat.com> <3c4d46c0-aced-f96f-1bf3-725d02f11b60@nvidia.com> <20181208163353.GA2952@redhat.com> <20181208164825.GA26154@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: On Sat, Dec 08, 2018 at 10:09:26AM -0800, Dan Williams wrote: > Another fix that may put pressure 'struct page' is resolving the > untenable situation of dax being incompatible with reflink, i.e. > reflink currently requires page-cache pages. Dave has talked about > silently establishing page-cache entries when a dax-page is cow'd for > reflink, but I wonder if we could go the other way and introduce the > mechanism of a page belonging to multiple mappings simultaneously and > managed by the filesystem. FYI, I had a a prototype for DAX + reflink that didn't require the page cache, although it badly reimplemented parts of it. But that was a long time ago, before we started requiring struct page for the DAX memory.