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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696604536; x=1697209336; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=LAT19evpcikftTKsU+k+vIv081WV5YPaM49e24ewPPI=; b=japxrGW2XNk1BiGC4fpm+ZNmNYCkJBr5IEMveGYOIEci+4BtW1PU6JbT12hfct3TWP 1A2NPH8ou2crFBZO2mHYGOn5LbAOTnSeQW+1MipthsmeA1JKmNZVhGHkDe4Yp6jxfFlI 3dNRbvBBvcrfSmWxbFddxa76h4mTrVBpxcMsuNAjmpdP/100UcSWH2VNlmdUkRelvsjV r5ercdOoJ6wNpEEPABXyXYZHkXUWKlbMIriiN8X0YqrK/Eeggis8IgMoB47lDauqVe1b NmmGLIRctnFepur0pZnAnQH9tHxS/wdS13iNLNptnpDOqhRA1X0/lYG3RM99XVmg6SJQ 64Wg== X-Gm-Message-State: AOJu0YxIxBVDOVyrpO9hATrFNVXDdVCJXBmQ+q1na4Ttt2qmtJc2mC5Z FjGUWnvh7riyZbRukK1mhQRAmELuvkyd+I8u3feKtg== X-Received: by 2002:a5b:807:0:b0:d81:6e88:7cb3 with SMTP id x7-20020a5b0807000000b00d816e887cb3mr7404835ybp.47.1696604534279; Fri, 06 Oct 2023 08:02:14 -0700 (PDT) MIME-Version: 1.0 References: <9434ef94-15e8-889c-0c31-3e875060a2f7@redhat.com> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 6 Oct 2023 08:02:00 -0700 Message-ID: Subject: Re: [PATCH v2 2/3] userfaultfd: UFFDIO_REMAP uABI To: David Hildenbrand Cc: Lokesh Gidra , Peter Xu , Jann Horn , akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-4.8 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_SBL_CSS,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Fri, 06 Oct 2023 08:02:32 -0700 (PDT) On Fri, Oct 6, 2023 at 5:30=E2=80=AFAM David Hildenbrand = wrote: > > On 04.10.23 01:39, Lokesh Gidra wrote: > > On Tue, Oct 3, 2023 at 11:26=E2=80=AFPM Suren Baghdasaryan wrote: > >> > >> On Tue, Oct 3, 2023 at 2:21=E2=80=AFPM Peter Xu wr= ote: > >>> > >>> On Tue, Oct 03, 2023 at 11:08:07PM +0200, David Hildenbrand wrote: > >>>> Sorry I have to ask: has this ever been discussed on the list? I don= 't see > >>>> any pointers. If not, then probably the number of people that know a= bout the > >>>> history can be counted with my two hands and that shouldn't be the b= asis for > >>>> making decisions. > >>> > >>> For example: > >>> > >>> https://lore.kernel.org/all/1425575884-2574-21-git-send-email-aarcang= e@redhat.com/ > > Sorry, I had to process a family NMI the last couple of days. > > >> > >> There was another submission in 2019: > >> https://lore.kernel.org/all/cover.1547251023.git.blake.caldwell@colora= do.edu/ > > It would be good to link them in the cover letter and shortly explain > why that wasn't merged back then (if there was any reason). Will do. I could not find the reason but will check again. > > >> > >> Though both times it did not generate much discussion. I don't have a > >> strong preference though MOVE sounds more generic to me TBH (it > >> specifies the operation rather than REMAP which hints on how that > >> operation is carried out). But again, I'm fine either way. > > > > That's a good point. IMHO, if in future we want to have the fallback > > implemented, then MOVE would be a more appropriate name than REMAP. > > > >> As for UFFDIO_MOVE_ZERO_COPY_ONLY vs UFFDIO_MOVE_MODE_ALLOW_COPY, I > >> find it weird that the default (the most efficient/desired) mode of > >> operation needs a flag. I would prefer to have no flag initially and > >> add UFFDIO_MOVE_MODE_ALLOW_COPY or whatever name is more appropriate > >> when/if we ever need it. Makes sense? > > > > Agreed! > > I agree. One could have UFFDIO_MOVE that is best-effort and documented > like that, and a to-be-named future extension that always works but > might be more expensive. > > > Ideally we'd have an interface that does not expose and/or rely on such > low-level information and simply always works, but getting that would > mean that we'd have to implement the fallback immediately ... so I guess > we'll have to expose a best-effort interface first. Sounds good. I'll try to post the next version early next week. Thanks for the input folks! > > -- > Cheers, > > David / dhildenb >