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[184.145.104.227]) by smtp.gmail.com with ESMTPSA id u126sm3664993qkd.80.2021.04.27.13.42.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Apr 2021 13:42:51 -0700 (PDT) Date: Tue, 27 Apr 2021 16:42:50 -0400 From: Peter Xu To: Axel Rasmussen Cc: Hugh Dickins , Alexander Viro , Andrea Arcangeli , Andrew Morton , Jerome Glisse , Joe Perches , Lokesh Gidra , Mike Kravetz , Mike Rapoport , Shaohua Li , Shuah Khan , Stephen Rothwell , Wang Qing , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, LKML , linux-kselftest@vger.kernel.org, Linux MM , Brian Geffon , "Dr . David Alan Gilbert" , Mina Almasry , Oliver Upton Subject: Re: [PATCH v4 03/10] userfaultfd/shmem: support UFFDIO_CONTINUE for shmem Message-ID: <20210427204250.GG6820@xz-x1> References: <20210420220804.486803-1-axelrasmussen@google.com> <20210420220804.486803-4-axelrasmussen@google.com> <20210427155414.GB6820@xz-x1> <20210427180314.GD6820@xz-x1> 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-kernel@vger.kernel.org On Tue, Apr 27, 2021 at 01:29:14PM -0700, Axel Rasmussen wrote: > On Tue, Apr 27, 2021 at 11:03 AM Peter Xu wrote: > > > > On Tue, Apr 27, 2021 at 09:57:16AM -0700, Axel Rasmussen wrote: > > > I'd prefer to keep them separate, as they are not tiny patches (they > > > are roughly +200/-150 each). And, they really are quite independent - > > > at least in the sense that I can reorder them via rebase with no > > > conflicts, and the code builds at each commit in either orientation. I > > > think this implies they're easier to review separately, rather than > > > squashed. > > > > > > I don't have a strong feeling about the order. I slightly prefer > > > swapping them compared to this v4 series: first introduce minor > > > faults, then introduce CONTINUE. > > > > > > Since Peter also has no strong opinion, and Hugh it sounds like you > > > prefer it the other way around, I'll swap them as we had in some > > > previous version of this series: first introduce minor faults, then > > > introduce CONTINUE. > > > > Yes I have no strong opinion, but that's probably the least I prefer. :-) > > > > Because you'll declare UFFD_FEATURE_MINOR_SHMEM and enable this feature without > > the feature being completely implemented (without UFFDIO_CONTINUE, it's not > > complete since no one will be able to resolve that minor fault). > > > > Not a big deal anyway, but since we're at it... Basically I think three things > > to do for minor shmem support: > > > > (1) UFFDIO_CONTINUE (resolving path) > > (2) Handle fault path for shmem minor fault (faulting path) > > (3) Enablement of UFFD_FEATURE_MINOR_SHMEM (from which point, user can detect > > and enable it) > > > > I have no preference on how you'd like to merge these steps (right now you did > > 1 first, then 2+3 later; or as Hugh suggested do 1+2+3 together), but I'd still > > hope item 3 should always be the last, if possible... > > In that case, I'll split the patch which adds the faulting path in > two: add the faulting path hook and registration mode, and then in a > separate commit advertise the feature flag as available. > > Then I'll order them like so, which I think is the order Hugh finds > more natural: > 1. MInor fault registration / faulting path > 2. CONTINUE ioctl to resolve the faults > 3. Advertise the feature as supported > > Sound okay? Good to me, thanks Axel. -- Peter Xu