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b=IvIVv5el6LnU28Qx7P2wrp8dYtLLm7swDE5IamqORJFQSIFhVlHcFXe9cwRn7iC1MLiuJm/BFqFS0mCni1E3Lgu7uXq3OGwb12qQFy65Pfqxmvtgp1yAQ73qkr0l/owpgcmEWssg6wMjkRBXM/JCnN9NpvF8SnwMERP1xv9LB4Y= Received: from 30.74.144.102(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WeeA-ii_1750729970 cluster:ay36) by smtp.aliyun-inc.com; Tue, 24 Jun 2025 09:52:51 +0800 Message-ID: Date: Tue, 24 Jun 2025 09:52:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] mm: shmem: disallow hugepages if the system-wide shmem THP sysfs settings are disabled To: David Hildenbrand , akpm@linux-foundation.org, hughd@google.com Cc: ziy@nvidia.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <52bc87c7dbd362d4d2b7780e66c1536fe99454a0.1750666536.git.baolin.wang@linux.alibaba.com> <924f82b1-0eb7-47e0-b7d4-5dd314df18a0@redhat.com> From: Baolin Wang In-Reply-To: <924f82b1-0eb7-47e0-b7d4-5dd314df18a0@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A9A47140003 X-Stat-Signature: zwz5im48wis9z63bc7o9c311zyzedanu X-Rspam-User: X-HE-Tag: 1750729975-890392 X-HE-Meta: U2FsdGVkX1+rHWMiaJR8kG7v3OyCt3FPGffuQLeIigPYgGCdX0Iqx6QoSQBTixttTVEHmpNLYoLTaQR6j4GJcR9AtV5uDSXvBZY5pRPIiRrwhBlq/ZtK8BQP1INH6r4Abw7VA/BLTtowWmZS615yIqNogwSQilG663OwI1f9zlIXYQK0krnILgJaCqzDHOdoyS+82EKz9FQ/YpzPbg2US/FM6VfZ+GzRA+qoNUD2vRvhXReffM0cqebWmYRP5JCmRxj+87r0mdJznhBbgAprhPXUw9jTgtjZEBhcSa/Fpr7n7rUmLHCd+jQPN4typ3PYu8vbeSSe/S0B5zpKlqsy3eL+hEqjHRNoj+fquswX/8YOgti+u1+gZdUFZjHTglAipQFmNSd7cGxyr1n4Yx09HLb2JrW6OUR8q/BmoufxFCUUaKDyvf1MWX1IXVHa7nKdZVxZgyf4muB3yYq8H8C+cbbvycAr/luh/P1uuJFyxrTkDDFtnVuDJ30gi6Ffz6NI3os0HRnSG4GAvr9ctW8CnMUgEaIEuNzNdIIt+PpB3fbXNFKEWqHwHH4wtwQuoa20pNLzW5EtmUaQ18hC+9CsIMMMLAT7vJzAg7Uyx4SuVdy91D/atxlttkSL2OmVI5GsxDiAWzcu/Fo83SrUiEv+yWQrvYqSJH1zn7ZrN8IMAxNrJxX1A7ufE/YmlS4QMaXyG39pN+HpsEmxTgUTPHo75G2M8i4rtznHBsLwQ+52OKyk6WuSmlb0GVEYkeI3p6RUwO0+BBZhX32E/f1HzOE3L0MP3WuJAiN/SFDCRFfhmDeKQroJ8a/AWlP2lKdOgY87c76qlcpp5xAP36WfhMKHpK0G1GYETKrddiFr86C7FanXhLa7Ue+jVcMGMf4+HZt3sacOV2RftN+5suwS5356ZTrulUogBritQjl1ZN/SNtE7hKh2ePDo+nuzxZAHKv9u9gYDaVWf9IiwR+HQBSO Z7yZ8E1J xi+JPTTrYYuwBcBWLzz8+VSipJ7YhaqLOMeakPFdZnHTvsjZFuWhnHi3e2qRSanYTN798VCM0MzG23erwY+fl7wBU3+cxV6byATt3xxVFat1eR76mmqdUNwKeE480J2yL8NwGpj7tQKaS7ZZ+5g92CHoTiQx5bwJYB9arHmjxpAZ4r5/c2VQlXG2LMWD0eUfJL2xoFMrUqx/cJNtUqwnY/QXgu6Bq7qCSlgDmCs4F3m89kvuIT2T7VFv8PriQpQdWxzWnJnY/VmDlEplFraSnDR7b36BTD2BSoAhG6mdV72SKt2FbNYOW/BbRaL7Fe5ubO4PwBDtG/O9LjnQDSVh0i9Yuf4vEgTJUGMV1 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 2025/6/23 21:59, David Hildenbrand wrote: > On 23.06.25 10:28, Baolin Wang wrote: >> When invoking thp_vma_allowable_orders(), if the TVA_ENFORCE_SYSFS >> flag is not >> specified, we will ignore the THP sysfs settings. And the >> MADV_COLLAPSE is an >> example of such a case. >> >> The MADV_COLLAPSE will ignore the system-wide shmem THP sysfs >> settings, which >> means that even though we have disabled the shmem THP configuration, >> MADV_COLLAPSE >> will still attempt to collapse into a shmem THP. This violates the >> rule we have >> agreed upon: never means never. >> >> Another rule for madvise, referring to David's suggestion: “allowing >> for collapsing >> in a VM without VM_HUGEPAGE in the "madvise" mode would be fine". >> >> To fix the MADV_COLLAPSE issue for shmem, then the current strategy >> should be: >> >> For shmem, if none of always, madvise, within_size, and inherit have >> enabled >> PMD-sized THP, then MADV_COLLAPSE will be prohibited from collapsing >> PMD-sized THP. > > I assume we could rephrase that to "For shmem, if "shmem_enabled" is set > to either "none" or "deny", then MADV_COLLAPSE will be prohibited from > collapsing." Yes. Setting 'deny' will also prevent MADV_COLLAPSE(), and there is no 'none' option for 'shmem_enabled'. Will update the commit mesasge to make it clear.