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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780894470; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nJZD1v0uKmRwmTPQY9fhrdbUR6X2mcRzW3srSSIJVBc=; b=BBmW8jOL6IGP4OdE9Tk2dDZ6XAZ07VWn9whCfkMIctmLJAFFQ8LHl3pqu76fyNCyFSDjaq tqprhwUKy/lu381KF5DjqtOYK7/1NHPLjz2i56t5p5q7L9rYSQF2gDaL7zqSaVdhlFOy1m 42nqER2YRyBfnjvZfD8in49rQbw+DNw= From: Lance Yang To: npache@redhat.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v19 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse Date: Mon, 8 Jun 2026 12:54:13 +0800 Message-Id: <20260608045413.70658-1-lance.yang@linux.dev> In-Reply-To: <20260605161422.213817-7-npache@redhat.com> References: <20260605161422.213817-7-npache@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: CDC3D1C000A X-Stat-Signature: 6y7tmxtmzj5y94nocdc7r6hyi3rqfo9p X-HE-Tag: 1780894472-234503 X-HE-Meta: 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 NnlplHQb DqxE3sO1GeyDTbg6CMwml3vnvQa6B4rpAOrt6bN4w8iYlZ7vJRAzaE9qwNb66pPvNPTO0+NfmFs3fHWmJgtY8F3ySIlF/P1J1rGzYkdBr4U+3SeBFHYBzpVR0fWB+c2kk6E0FWEPxvYEHs5wx7I9H1N4rrbxaAqNAHjarbM9DSVZYooSls/OZOvN/hmGyS6nx+wLOBVZ9R5WO+iXTsgVIe3fBq5Ow0PqNqa7SS/rfYVzdEQeeTuH/udG9khirBtKC4QgECWCL4tTVoEBQfaYiow+Upd0sMhemW0zKMgEMmvFZgM7CQtPD2eQOYt5A8qYf2mblQaVdpGN7Up9J8tf3FEkEytMfoeONIwSN Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 05, 2026 at 10:14:13AM -0600, Nico Pache wrote: >Pass an order to collapse_huge_page to support collapsing anon memory to >arbitrary orders within a PMD. order indicates what mTHP size we are >attempting to collapse to. > >For non-PMD collapse we must leave the anon VMA write locked until after >we collapse the mTHP-- in the PMD case all the pages are isolated, but in >the mTHP case this is not true, and we must keep the lock to prevent >access/changes to the page tables. This can happen if the rmap walkers hit >a pmd_none while the PMD entry is currently unavailable due to being >temporarily removed during the collapse phase. > >To properly establish the page table hierarchy without violating any >expectations from certain architectures (e.g. MIPS), we must make sure to >have the PMD reinstalled before the PTEs, and hold both PTE/PMD locks >before calling update_mmu_cache_range() (if they are distinct locks). > >Signed-off-by: Nico Pache >--- Nothing else jumped out at me. Anything left can be sorted out later, as David and Lorenzo said :) Reviewed-by: Lance Yang