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Thu, 03 Jun 2021 12:24:59 -0700 (PDT) Received: from smtpclient.apple ([2600:1010:b04a:17e9:b873:a3cc:f7b1:9d6d]) by smtp.gmail.com with ESMTPSA id n23sm3300321pgv.76.2021.06.03.12.24.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Jun 2021 12:24:58 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read Date: Thu, 3 Jun 2021 12:24:56 -0700 Message-Id: <1FD047D2-F5F3-4AC6-A4E4-DB8FB1568821@amacapital.net> References: Cc: Hugh Dickins , Ming Lin , Simon Ser , Linux-MM , Linux Kernel Mailing List , linux-fsdevel , Linux API In-Reply-To: To: Linus Torvalds X-Mailer: iPhone Mail (18E212) X-Rspamd-Queue-Id: 8B72DA00027D Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=amacapital-net.20150623.gappssmtp.com header.s=20150623 header.b=YHJtOqmP; spf=pass (imf15.hostedemail.com: domain of luto@amacapital.net designates 209.85.210.173 as permitted sender) smtp.mailfrom=luto@amacapital.net; dmarc=none X-Rspamd-Server: rspam04 X-Stat-Signature: hshsu1yx8unyd95n7xa4kn9uoy5s6ixc X-HE-Tag: 1622748293-356337 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 Jun 3, 2021, at 12:14 PM, Linus Torvalds wrote: >=20 > =EF=BB=BFOn Thu, Jun 3, 2021 at 12:07 PM Hugh Dickins w= rote: >>=20 >> But the point that we've arrived at, that I'm actually now fairly >> happy with, is do *not* permit MAP_NOSIGBUS on MAP_SHARED mappings. >=20 > Yeah, if that's sufficient, then that original patch should just work as-i= s. >=20 > But there was some reason why people didn't like that patch > originally, and I think it was literally about how it only worked on > private mappings (the "we don't have a flag for it in the vm_flags" > part was just a small detail. >=20 > I guess that objection ended up changing over time. >=20 >=20 I don=E2=80=99t understand the use case well enough to comment on whether MA= P_PRIVATE is sufficient, but I=E2=80=99m with Hugh: if this feature is imple= mented for MAP_SHARED, it should be fully coherent.=