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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=mZGrVUx3DEBnxNLMA2Y+MW04SIp2tP/blTyUA/uLcUt4gRgO2HXiwHIwtT7CAV1wd JcNAjtANaSLbKoycdA2J/acacoXg0TXN8MxrqEgjdbq86A+KsrIW3YxOgJUxADMdXz 08Ssf3Vulb9ZpmV5GeHKclrnsPhxNGuiSs8Qqr6A= Date: Sun, 13 Sep 2026 19:43:27 -0700 From: Andrew Morton To: Baolin Wang Cc: hughd@google.com, david@kernel.org, ziy@nvidia.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, ljs@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: shmem: ignore sysfs configs for shmem forced collapse Message-Id: <20260913194327.019b3db96ea9b0719fc147f7@linux-foundation.org> In-Reply-To: <063f655b4d6c4234f3aa27ed6ecab10283ecb880.1789351825.git.baolin.wang@linux.alibaba.com> References: <063f655b4d6c4234f3aa27ed6ecab10283ecb880.1789351825.git.baolin.wang@linux.alibaba.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 530F640005 X-Stat-Signature: qijudubizsj51bor49h3q4zqrtsn9qjc X-HE-Tag: 1789353809-321696 X-HE-Meta: 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 YJVZL5hh mKFjoW18MWV6NSvpCKxrbewoxYs0qQVxdp+7V7wrEvNCkks8gDUs+7FD0YNN22Uxoaqt4KdPfJ3aPm8IXGppb3RJbJ3KeUFx3wxdY7zEHwb792jemWBF3ojtQK5xbUw9av5T1zp9g8m78uOR7PMz+I+Y/CyLkDc9tjSHDYT5FM8Jv4MJRHxlM+36NI0bGQzijxxYi2Hne4knjW28ttM1VunjTsiV7lsHi7kgu5Id71Ug7mHazun8gD8oNXHa2cPlytVS/H2lm4+AJ6bNVtx8Xe+doPsAxwy4lymZn8GtGtOtvyZk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 14 Sep 2026 10:12:41 +0800 Baolin Wang wrote: > According to Documentation/mm/transhuge.rst, MADV_COLLAPSE is expected to > ignore any THP or mTHP interface settings. > > However, after commit 26c7d8413aaf ("mm: thp: support "THPeligible" semantics > for mTHP with anonymous shmem"), performing MADV_COLLAPSE on shmem will > depend on /sys/.../hugepages-2048kB/shmem_enabled being set to "inherit" > (although that is the default), which can cause MADV_COLLAPSE to fail > unexpectedly. Userspace-visible runtime regression? > Fix this by returning the result of shmem_huge_global_enabled() directly > when MADV_COLLAPSE is requested, allowing PMD-order collapse while ignoring > shmem THP/mTHP settings. > > Fixes: 26c7d8413aaf ("mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem") Should we backport?