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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id i7-20020a056214030700b006215f334a18sm3542109qvu.28.2023.05.15.15.05.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 May 2023 15:06:00 -0700 (PDT) Date: Mon, 15 May 2023 18:05:58 -0400 From: Peter Xu To: Yuanchu Xie Cc: Andrew Morton , "Liam R . Howlett" , Yang Shi , Zach O'Keefe , "Kirill A . Shutemov" , Matthew Wilcox , Pasha Tatashin , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: pagemap: restrict pagewalk to the requested range Message-ID: References: <20230515172608.3558391-1-yuanchu@google.com> MIME-Version: 1.0 In-Reply-To: <20230515172608.3558391-1-yuanchu@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: 9pz4zcgwgqi7d4dh4an5t6fqxipypg6q X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D7535160011 X-Rspam-User: X-HE-Tag: 1684188363-316520 X-HE-Meta: U2FsdGVkX18CdlmfGvFdbzIg6vtjNOrdLaSAmgr3nUw5h8ZSJhBj1NrA1GYIXbuSmOgV+5Xi8CVuf8X7vkGd0Nc5dVAaOsfuEExueiXb4ceRuUF5o8Uwi10fk+4qfLqRznLoHPa1uPJE82VZClqNLYBlMdMwTNwEPGwQYD9IBp2RcKvklXFA+pOWOBnLEqTTCIPPANHP2kQIhTQAQilfr/3TeRuVmy5nvfGhAuTqiJ7cpLenjYz6MwoZktsaIeED7836L4m9iFKS/GPFRD4HgyxlGuSXzsfvBik1W9VhYDA3YYAjBdVzpQHvU4fvkOzyn0LnSZ8g2JyLB5FJ1m2NOlRSmrNdRVDbbxQFgKLJ87ELVjLoBXQ8xU5eqDCkLnSb142CPgKAAIDoSSAd+anOr6Jl34XcO5LSMOBL33OrjRbgWOn3QiXAQXxVcFnhijHXtoLPNHX7koMljr5p+yqodRLumV1ORTlwCEdXmY1FTUXQYyteSeRViVLNJj0d/8iFbCTeMFzekjtJCHRhqm6R6IvFR8IJKfw63t+WY7UJnkwbxE9gnj4ipPwoTNCY/KYXMkCjmRge3XV1UacJlGsTXX2/IV5H7hAux9Fr2Ja+/GNTojYZhF/7Q9awtneBexNeFvUrJOBbCEBUD6vll3tmWptXDrXpOk4nv5jcueXBCaJwu7I4BSDc9tKYVFBNP2O1mGjXj1O6+YOodiyhMUVaQYcCNqUzNplPb5yy6pGFDV9nPSqWiKFb6lI9sUNpA/nFoJAOS6i9CrMD0uCUiHfp5QCJh/U6G1BbHqIn41v7mn5WZCtgbGG2hHWIuU4ShYEcTteljN+RVO7lgoHnHw8+GVaZ+g0U8+uu7g3cJgG63gPi0VEY6VjXe6709wBQo4IZ1ptn2Ax3x3pqP3ey5A3UwNUJ8mVa5BpCYLmF96ODWutWvAMNiRZ5XFYcgVVjcJQAvkP18J4AZFLfgsZuCrV dDQd1gqF R+rftjrTdY6nGnOBzRvM+7CM5ATAEJmZLlHY9BprpqNTe8I7J6h01n5/nZmWyf2cHbvyZoL6Q/qw/grVvP3NsUw0XVG1hZn3C6OK3h7uEwBDEkq/zOY6BWvFCTNFP/6Qt74YHIJkznVFYJd/pYpnSHDqsKFvV4yWbQBAg7+UwI1u/FHchHMXXYUY4O1Ij9RMlSVs6/H/COe5VwSqp6Sgb6/Iz/RmpHO0+EwHKmYVONI3vT9VXcuuLbmxpdyjHFSvbrX5Pi6PoGkgumFs7RgoULTVdQWBBjsGt8neQ7EZw/YYyeuNQ/LHm3MthXWZRrt+UdsNMdGnr5qrXGmH+R8Vm5ZtYDSMlPDQYhGDYpgziehylPhxe2STyCIVYsLjyzu2Gyl0iBNFVWiQP4Qc3GuuIAMi/vimyXzbvoAUEiKImiWb2DpWfDIzut4jjUQ== 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, May 16, 2023 at 01:26:08AM +0800, Yuanchu Xie wrote: > The pagewalk in pagemap_read reads one PTE past the end of the requested > range, and stops when the buffer runs out of space. While it produces > the right result, the extra read is unnecessary and less performant. > > I timed the following command before and after this patch: > dd count=100000 if=/proc/self/pagemap of=/dev/null > The results are consistently within 0.001s across 5 runs. > > Before: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s > > real 0m0.078s > user 0m0.012s > sys 0m0.065s > > After: > 100000+0 records in > 100000+0 records out > 51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s > > real 0m0.050s > user 0m0.011s > sys 0m0.039s > > Signed-off-by: Yuanchu Xie Acked-by: Peter Xu -- Peter Xu