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Tue, 15 Sep 2026 06:46:00 -0400 (EDT) Date: Tue, 15 Sep 2026 11:46:00 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, ljs@kernel.org, nico.pache@linux.dev, baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, ziy@nvidia.com, usama.anjum@arm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, jannh@google.com, willy@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 00/57] mm/collapse: rebuild collapse on migration primitives Message-ID: References: <20260816224609.308019-1-kirill@shutemov.name> <9f51ac27-24b2-495b-b397-84865f977d24@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Sep 14, 2026 at 05:07:37PM +0200, David Hildenbrand (Arm) wrote: > > As I mentioned above, we drop the ptl after the freeze. And take it a > > second time for the install. Allocation and the copy run in between with > > no lock held -- on 64K the copy at PMD order is 512M of it, which is why > > it cannot sit under either lock. > > Hold on, are freezing all folios to collapse? That cannot possibly work with > COW-shared folios that are mapped into other address spaces. I break COW for worthy candidates in the faultin prepass before freeze, alongside swapin. It simplifies the picture substantially. No rmap mess. -- Kiryl Shutsemau / Kirill A. Shutemov