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Sat, 10 Jun 2023 22:20:32 -0700 (PDT) Received: from [2620:0:1008:15:9d66:9274:d797:9fc7] ([2620:0:1008:15:9d66:9274:d797:9fc7]) by smtp.gmail.com with ESMTPSA id p14-20020a63e64e000000b00547a122d3fcsm5305193pgj.71.2023.06.10.22.20.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 Jun 2023 22:20:32 -0700 (PDT) Date: Sat, 10 Jun 2023 22:20:31 -0700 (PDT) From: David Rientjes To: Josh Triplett cc: Andrew Morton , Mike Kravetz , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [PATCH] mm: hugetlb: Add Kconfig option to set default nr_overcommit_hugepages In-Reply-To: <88fc41edeb5667534cde344c9220fcdfc00047b1.1686359973.git.josh@joshtriplett.org> Message-ID: <71834e10-098c-7d15-b9d4-36d33a57499c@google.com> References: <88fc41edeb5667534cde344c9220fcdfc00047b1.1686359973.git.josh@joshtriplett.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5CD5F80004 X-Stat-Signature: iamcy5sic6y3qtcznqsh8z8swbs3hkgs X-Rspam-User: X-HE-Tag: 1686460834-704326 X-HE-Meta: U2FsdGVkX19kbb/jgkdJC+tdZgmENp6sJonW1swhw2LAtx7zE4VZuYLvUca1Ul7KpEALaIUrl6rEZzh1YyVN+dqgK0aaklztAiO/OenvDmEsWflc2P0kPDOJf9pCG9SbeKyp36pCs+NxHSO0J8VpWvO8suMfn86la6Hi8HdCuq2ZzDp06TOVGKwcq5QUw3hOW5dor8I+tlVJ8xDzMU4YerCoipOwAH20/pOWvjcGyryHFnm4t7rhB3EYXx9NRzWynCNI2nZQ6F//6KigQTWUiM0OgPWBZORdYHkpWYq0FdpSKFAoXP7VD1uNzJ88hLE/zp+HllA5MkG25iE5fHkeAv4xfxOTKS9/z1PSt/QU5E7x/iMUM1J9DOvPTDSuhvcwRG671lNLpFuIr7YEtxSOWt+LwdW/kN/uPVSwnMh8zeSl8v5NH/Nu3Nby6viZVDf21x1OifDI/6IrV/SBoNDUhuCDj3JY3rKsEeYyd8TWJAVZqO4giXfH3QknQ5rYmNaCrHPtlQt2lifRpcOP5mYjBJunhVL1uaWMdLch1ISem7jOI+LtgG6eu7LDMHs8bRcBsbTbVqSOv+ejIma5wE/SR17pOa7G68ENL32Gahtzr088drPwUZCOwY+APV8OZJ+50l9Q/FFdPKF3QrbD/2ne1uRRtlqth+A0sIvEaf6FaKksEhvmqSbuoDlZxtJ3dXH6FkXzPX8n1BAxYLX2FaPn5LYjnIiaMg9yNqwy87tbnuzpClUDCh4+MsrMkVQLu4grhGKBaHXdWeDf2QPYcZs2bNi5Ql8zcEzjFfIXkde75JFp3xYefO8/DEe1w3HeZ1AsILZtE+K8swA8uauZEjqtN/PyDSI0BRFqmLcng6GPkc4Bod8Sv/mMbCnjg3wBKz8eU5hyUnxXPeLrnc/9l6q5hzTErPKx/fl/MRcdli7aNZLymTgBau7eMAN1dYY3l5Y75z+CiHeaIDqIp3sOu6m Lv6fTCzK uLtfqtGvHIiNjfDpzWlRt2FFczctOIcqQzCDpsKmzLbThDmFmvQlEm7uiJdc+C7QqUxo0wxTqKGoWd3a7zaUeoO6YWsfO/yYOjJDmkZuSr3Rc8jQcJSVwak0WlyeXAY/uMBkPPKQKMzVZXl9j+yIdNNMMW7UdP/K7S71u5M/3z3JWmffRzdKDFRwFaolXAJe2mQZniuGjp0UwNDyP0huPdrewtSa2+0M/6tiLfGmPKzirNyr9sRoxYQuFRQgtkKJA6zmXdBfgdi/y1IahFuUBX+HpeInlRgOzvkdz4788yFoUX93Uj2Sp65bGZ90YgIN++wg0kg5UjjcAqkboz4mNGgi5804ymv2ApARujKBLOwnV0wxCjWKxGwMVYyf0iORZgj6WKEokFQc5nUr2SeYNJDat5cEAbu2jeFQDNVdCk1XK2VpFR98wPECxpfVSk22FsNdVXeIj0HtlwJecUDl+Br5TBAapkVp4KSoi 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 Fri, 9 Jun 2023, Josh Triplett wrote: > The default kernel configuration does not allow any huge page allocation > until after setting nr_hugepages or nr_overcommit_hugepages to a > non-zero value; without setting those, mmap attempts with MAP_HUGETLB > will always fail with -ENOMEM. nr_overcommit_hugepages allows userspace > to attempt to allocate huge pages at runtime, succeeding if the kernel > can find or assemble a free huge page. > > Provide a Kconfig option to make nr_overcommit_hugepages default to > unlimited, which permits userspace to always attempt huge page > allocation on a best-effort basis. This makes it easier and more > worthwhile for random applications and libraries to opportunistically > attempt MAP_HUGETLB allocations without special configuration. > > In particular, current versions of liburing with IORING_SETUP_NO_MMAP > attempt to allocate the rings in a huge page. This seems likely to lead > to more applications and libraries attempting to use huge pages. > > Signed-off-by: Josh Triplett Why not do this in an initscript? Or, if absolutely necessary, a kernel command line parameter? A Kconfig option to set a default value to be ULONG_MAX seems strange if you can just write the value to procfs.