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[184.145.104.227]) by smtp.gmail.com with ESMTPSA id q26sm1313209qkn.81.2021.04.27.11.03.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Apr 2021 11:03:16 -0700 (PDT) Date: Tue, 27 Apr 2021 14:03:14 -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: <20210427180314.GD6820@xz-x1> References: <20210420220804.486803-1-axelrasmussen@google.com> <20210420220804.486803-4-axelrasmussen@google.com> <20210427155414.GB6820@xz-x1> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 87211E000127 X-Stat-Signature: jc6rnc8mtac91nzrm5nqbuaaxa455rga X-Rspamd-Server: rspam02 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619546581-931605 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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... Thanks, -- Peter Xu