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[209.85.208.53]) by smtp.gmail.com with ESMTPSA id r8-20020a170906c28800b00969e9fef151sm1089181ejz.97.2023.05.25.10.13.56 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 May 2023 10:13:56 -0700 (PDT) Received: by mail-ed1-f53.google.com with SMTP id 4fb4d7f45d1cf-510dabb3989so5006444a12.0 for ; Thu, 25 May 2023 10:13:56 -0700 (PDT) X-Received: by 2002:a17:907:a49:b0:96a:498a:bd4b with SMTP id be9-20020a1709070a4900b0096a498abd4bmr2248713ejc.64.1685034836175; Thu, 25 May 2023 10:13:56 -0700 (PDT) MIME-Version: 1.0 References: <20230522205744.2825689-1-dhowells@redhat.com> <3068545.1684872971@warthog.procyon.org.uk> <3215177.1684918030@warthog.procyon.org.uk> <88983.1685034059@warthog.procyon.org.uk> In-Reply-To: <88983.1685034059@warthog.procyon.org.uk> From: Linus Torvalds Date: Thu, 25 May 2023 10:13:39 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Extending page pinning into fs/direct-io.c To: David Howells Cc: Christoph Hellwig , Jens Axboe , Al Viro , Matthew Wilcox , Jan Kara , Jeff Layton , David Hildenbrand , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 65g6ek1bz37be5s8w465d6jgb4io9x46 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EA48D20010 X-Rspam-User: X-HE-Tag: 1685034838-109417 X-HE-Meta: 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 VZGVYBc5 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 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 Thu, May 25, 2023 at 10:01=E2=80=AFAM David Howells wrote: > > What do we gain from it? Presumably since nothing is supposed to write t= o > that page, it can be shared in all the caches. I don't remember the details, but they went something like "broken purely virtually indexed cache avoids physical aliases by cacheline exclusion at fill time". Which then meant that if you walk a zero mapping, you'll invalidate the caches of the previous page when you walk the next one. Causing horrendously bad performance. Unless it's colored. Something like that. I probably got all the details wrong. Linus