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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id u18-20020a05622a14d200b003f3937c16c4sm1457623qtx.5.2023.07.28.14.49.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jul 2023 14:49:15 -0700 (PDT) Date: Fri, 28 Jul 2023 17:49:13 -0400 From: Peter Xu To: John Hubbard Cc: David Hildenbrand , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , liubo , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout Message-ID: References: <20230727212845.135673-1-david@redhat.com> <69a5f457-63b6-2d4f-e5c0-4b3de1e6c9f1@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hello, John, On Fri, Jul 28, 2023 at 02:32:12PM -0700, John Hubbard wrote: > On 7/28/23 14:20, Peter Xu wrote: > > On Fri, Jul 28, 2023 at 11:02:46PM +0200, David Hildenbrand wrote: > > > Can we get a simple revert in first (without that FOLL_FORCE special casing > > > and ideally with a better name) to handle stable backports, and I'll > > > follow-up with more documentation and letting GUP callers pass in that flag > > > instead? > > > > > > That would help a lot. Then we also have more time to let that "move it to > > > GUP callers" mature a bit in -next, to see if we find any surprises? > > > > As I raised my concern over the other thread, I still worry numa users can > > be affected by this change. After all, numa isn't so uncommon to me, at > > least fedora / rhel as CONFIG_NUMA_BALANCING_DEFAULT_ENABLED=y. I highly > > suspect that's also true to major distros. Meanwhile all kernel modules > > use gup.. > > > > I'd say we can go ahead and try if we want, but I really don't know why > > that helps in any form to move it to the callers.. with the risk of > > breaking someone. > > It's worth the trouble, in order to clear up this historical mess. It's > helping *future* callers of the API, and future maintenance efforts. Yes > there is some risk, but it seems very manageable. > > The story of how FOLL_NUMA and FOLL_FORCE became entangled was enlightening, > by the way, and now that I've read it I don't want to go back. :) Yeah I fully agree we should hopefully remove the NUMA / FORCE tangling.. even if we want to revert back to the FOLL_NUMA flag we may want to not revive that specific part. I had a feeling that we're all on the same page there. It's more about the further step to make FOLL_NUMA opt-in for GUP. Thanks, -- Peter Xu