From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 13 Dec 2018 15:56:05 +0000 From: Christopher Lameter To: Jerome Glisse cc: Dave Chinner , Jan Kara , John Hubbard , Matthew Wilcox , Dan Williams , John Hubbard , Andrew Morton , Linux MM , tom@talpey.com, Al Viro , benve@cisco.com, Christoph Hellwig , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , mike.marciniszyn@intel.com, rcampbell@nvidia.com, Linux Kernel Mailing List , linux-fsdevel Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions In-Reply-To: <20181213020229.GN5037@redhat.com> Message-ID: <01000167a8483bd2-16ae0d3e-d217-4993-a80a-25d221c677e4-000000@email.amazonses.com> References: <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> <20181208022445.GA7024@redhat.com> <20181210102846.GC29289@quack2.suse.cz> <20181212150319.GA3432@redhat.com> <20181212214641.GB29416@dastard> <20181212215931.GG5037@redhat.com> <20181213005119.GD29416@dastard> <20181213020229.GN5037@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: On Wed, 12 Dec 2018, Jerome Glisse wrote: > On Thu, Dec 13, 2018 at 11:51:19AM +1100, Dave Chinner wrote: > > > > > [O1] Avoid write back from a page still being written by either a > > > > > device or some direct I/O or any other existing user of GUP. > > > > IOWs, you need to mark pages being written to by a GUP as > > PageWriteback, so all attempts to write the page will block on > > wait_on_page_writeback() before trying to write the dirty page. > > No you don't and you can't for the simple reasons is that the GUP > of some device driver can last days, weeks, months, years ... so > it is not something you want to do. Here is what happens today: I think it would be better to use the established way to block access that Dave suggests. Maybe deal with the issue of threads being blocked for a long time instead? Introduce a way to abort these attempts in a controlled fashion that also allows easy debugging of these conflicts?