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Received: from 30.97.56.69(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W62EHYc_1715143509) by smtp.aliyun-inc.com; Wed, 08 May 2024 12:45:10 +0800 Message-ID: <0b3735bc-2ad7-44f8-808b-37fc90d57199@linux.alibaba.com> Date: Wed, 8 May 2024 12:45:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/8] mm: shmem: add multi-size THP sysfs interface for anonymous shmem To: Ryan Roberts , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <6b4afed1ef26dbd08ae9ec58449b329564dcef3e.1714978902.git.baolin.wang@linux.alibaba.com> <30329a82-45b9-4e78-8c48-bd56af113786@arm.com> From: Baolin Wang In-Reply-To: <30329a82-45b9-4e78-8c48-bd56af113786@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: r8ywubhzmh6p3xhfge4dgizufuw3ztnf X-Rspamd-Queue-Id: 9722212000C X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1715143515-745844 X-HE-Meta: U2FsdGVkX18KKJYHtzAs7mgz9bPOHJx4LTQileh2cr9fAjuGuRppyxz2A/zXyPg1fYvxXOxyKhfBiesmRipwp2KmcpsYSHUb3U1mp7GwJTdt6tSMimng/+RP1V+Uv+2nU34mPYqr8y2ry5f0Ax/Lae4vGsx88eKHVh4bkXgfcBVBaEwVEveOBgE65T7p8F3a88KsyV0UkDRXT3p+DRMYjLD6+Kl4jKtyZ0Um4/rssIzCRRibdmMUluOcJOP71Yi0zvSJMbhDEH0X3vznbCtYSg91Z1hbaVGYJUIDhIuY9S6fASiSBj1X+k/Mxh2nJjyvYwlInYXzpAfwP9E/gxeEXs0HED3zPyQC8lF4wSKXHi0+vJR6vdlpjpIFLBPSUerZKJcIP3Tib8xTeeqtj+FKEy9idb0erLnk8DYFaeU4aOrOlEST7O156FwQTz0cz7FBBnY4AUdHfYdAIuah9ykpEN9JPszFMFHOCiDe5cWNAZpwC/oV+dkbMHxnbuvB2jA5TrwxtevA149LAsYW5iUxp5ZiiRbTyfiCmN/mDOMUk0csnv8URaLbs1cezNrJoJmrLbViFy3acjrfUXbf8GCD926EcDGSvmDEC72n17tlXQuv/SkqO1pMZo9u/G2B2LxUtvkjMxwGXhmf5NgPDL2+68A54wuKT2LLRsoq0kVA8nVmSkPrFM/BOi0rNVETNmy4iR7K1TzczKDr//8cLo9vohNxC93i0HXXbGnfc1PICxolT5Y4CwPyZ1r7qy6hAAdySavzZv/KG93JDNcu5641eFTmcAf2ct2rNhDitYqqf/ZqzGk4txoJCqUblsfniUQCjgziWwMNCAoiddCt1CYl6KZziP+4e6rAcuOYtOMyVlf+jBXV93pLaT0TQSEv4n8eh3fAYlqQ4T2mmZ1Pk+3uJUGIbI8YK69/79laqPoTOwIGjvBmn9W7gKunZj89cBwqL5zqExTKyEfrXGu/csd I9svJQZr Nu9e/D9yKwtJXyZQK8/qD6SiGCiHBTweAOUzhdLHb3/m/T/iuQUc4rH8+NQCoPsFi2Xkdti7U2DDA6IhFcx6xfbMzh2H8TGIInzRV6M8GedDqx0q2+LqPcX1FSskteQhhrb/opPl5syapeu22hFxl6TkG9rMWE6kZDa7GNwABEkOip8Orm4AZUhBoXQ14SPJjEZjoMmYStg7XTM4sw1/0hZ6cbeaRbJT89YutyOGI/rxh3FPh/uM3KM48L95IQGvOext3RgwJd5tDUceYtc+t+QqIcLeA2qe95DcKAvnuxEhjTDIM4AFn5N8aIsGhbVG6GiiU4VMzFqcOhkXzO2BfDbAFYL19Er8VkLTuKu54jwBV1jnoVmXLdufalZ2zq1t7gjwX 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: List-Subscribe: List-Unsubscribe: On 2024/5/7 18:52, Ryan Roberts wrote: > On 06/05/2024 09:46, Baolin Wang wrote: >> To support the use of mTHP with anonymous shmem, add a new sysfs interface >> 'shmem_enabled' in the '/sys/kernel/mm/transparent_hugepage/hugepages-kB/' >> directory for each mTHP to control whether shmem is enabled for that mTHP, >> with a value similar to the top level 'shmem_enabled', which can be set to: >> "always", "inherit (to inherit the top level setting)", "within_size", "advise", >> "never", "deny", "force". These values follow the same semantics as the top >> level, except the 'deny' is equivalent to 'never', and 'force' is equivalent >> to 'always' to keep compatibility. > > We decided at [1] to not allow 'force' for non-PMD-sizes. > > [1] > https://lore.kernel.org/linux-mm/533f37e9-81bf-4fa2-9b72-12cdcb1edb3f@redhat.com/ > > However, thinking about this a bit more, I wonder if the decision we made to > allow all hugepages-xxkB/enabled controls to take "inherit" was the wrong one. > Perhaps we should have only allowed the PMD-sized enable=inherit (this is just > for legacy back compat after all, I don't think there is any use case where > changing multiple mTHP size controls atomically is actually useful). Applying Agree. This is also our usage of 'inherit'. > that pattern here, it means the top level can always take "force" without any > weird error checking. And we would allow "force" on the PMD-sized control but > not on the others - again this is easy to error check. > > Does this pattern make more sense? If so, is it too late to change > hugepages-xxkB/enabled interface? IMO, this sounds reasonable to me. Let's see what others think, David?