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Fri, 10 Apr 2026 11:38:55 -0400 (EDT) Date: Fri, 10 Apr 2026 11:38:54 -0400 From: Andres Freund To: Zi Yan Cc: "Matthew Wilcox (Oracle)" , Song Liu , Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v1 05/10] mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled() Message-ID: References: <20260327014255.2058916-1-ziy@nvidia.com> <20260327014255.2058916-6-ziy@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4C847140002 X-Stat-Signature: af8gyohtdwk157z8ejp7bt1c61p4mjee X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775835537-443233 X-HE-Meta: U2FsdGVkX19a72PGlIzF5W2umX0DotVg97mkTJ9H/Pf9Rm2E1n/Lr6/nc8oDNvLq0jbi161NHZm8+bGCkmoNSFQuEttBU/vW94ujbsCa1TxEOJSQAS1xgLAw3tPC76uUBeV2NliSJlYEwWGlhIqwL/iqjNMPYwfzAYqkySa813m/LlEUPbHy4vb/7q3SOLdZwNPdXvm77Ujr1MipC9G9V7TA/o/HNjPc+yk5EnOQLCfByRNYT/CwomwBFOnRxabhJjoo1P2JGh6HDUenjqGOI5d4oEbYxfzpgSoOrv0ZguH8c26NGQsL6HYhUuYrbqCrGbOeQV2ENewTOm0OotS20LdPUn5sn9OkVeFAkL23gqs/ZZw3q5AR1LwboX/pc2SPYXWih/067Wic2jT8IQR6zVXZaIxywjytC4gtZWEyzEMopmivnF2ktR6kQVYMn1CE7gKfublOFBDbirKRWb7hDS2fNIh0I0kRVu32gV4/yrVXJA3/Gc2VpRfyHYGenhoH+GShaPPWmB8J7gQCP+NEHyJ7s6dGYX0KXTzbGDgMVvY4kQw5ppnmsYl+uIPJREbWiRxCh/b0Q1g677NDduGcDUedzsuAE60b/sVuvXSP3bGbfIRDYHLxLzaGjyH2sJIcxvkK/LvEWvE3mdcl60t34INFnvpy2iOf56fbrkrEXSrLkfQxWgPLCaoUQ57u6cmy7uPNtA5s1RpwqS/8EhF32DDrkDr5bNCbUrJNrBpCkZMao8MN9YEW4pOMXW1cwq8Cr0nw4bHQ38AIxmBqkRlVILcflpvzPMzEq1lQVhLUXtxMS/waGGicm5Rk7myIlJvzV6GbxJ/EqYiKqSjeFmo1woy3qDxTqbKTFaHB8DrMW951cRY7kqUa5i63b35Kjzbhs3jp8OYYGI8lZnh+/r7p5MmndboJQcrZyPZoHflX+EyrWz66rhkix8OXV6+dHi84k+NenDjUrJbxzr5CM2G 1PsIUHCt NZYCHTlzEsckTR3WBBBkajTI+LwLYE/+KoXf8kiOcbCWwJXTnD8um2A4LxR4SkRPi9EAZ+TgB9oQWuTXI0KGAwhC6t13cbRr/lDFzct4EAxhUz5bzsXjOeI7tTZ3F7ePtKygghfSeAvt6Q76MgM92ljXXhy2RS198p1uz2gjGDji8ShdrnF5r6l2JgBq22CAQ7RrRCehAplSwnngLCG/KUPG+/eHSlHhFLLTicYhoLaZ0u/9sQRQshzqlNJwjitnXEORWE898g+8f4pjj+TfHSbstXtZSsG+HzfU7ApnJsdE+BBurQaECPG7QE8G9f6OWYz1OBtm7/iUHDYNY8GTJ0nMriWm5r9k5xhiIOK219K9T7PSxSnD5Nbc1arBQrQlDGr+sfVgTfnuZtxm9o0/B9rWaug== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, On 2026-04-10 11:18:24 -0400, Zi Yan wrote: > On 10 Apr 2026, at 11:06, Andres Freund wrote: > > On 2026-03-26 21:42:50 -0400, Zi Yan wrote: > >> Replace it with a check on the max folio order of the file's address space > >> mapping, making sure PMD_ORDER is supported. > > > > Question from a user space developer (who learned of this via LWN [1]): > > > > Right now MADV_COlLAPSE on file mappings appears to only only work with > > CONFIG_READ_ONLY_THP_FOR_FS. > > > > That's pretty sad, because I see quite consistent gains (~15%) from doing > > madvise(MADV_COLLAPSE) on e.g. postgres' .text - but because > > CONFIG_READ_ONLY_THP_FOR_FS is not enabled default (or at least not commonly, > > I think?) in distro kernels, it never quite seemed worth the fiddliness. > > > > > > Do I understand correctly that by replacing the check here (and the > > predecessor commits), madvise(MADV_COLLAPSE) on file mappings might actually > > start working in more situations on typical distro kernels? > > Yes, assuming your file system supports PMD THPs. > > Based on[1], ext4 and xfs have the support, btrfs supports large folio but > not up to PMD order. I have not checked other FSes supporting large folio[2]. I personally only care about ext4 and xfs, so this is awesome. Thanks, Andres