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b=K3W8lDCm6YecnNVEKENAO2Z6Sg7cT/3eLRojKTT6Z9zscAa/v/5cqGv3GNPCLAGEp 535X6IYjYQnPdQSkuW0jarjrIMu8TG3MAad+tPqdtJJd80EQSMeNM67ts1y4gFv9Mh 3shg6wfIiE7m9n6ku2qbiiPe+vdifcqzKk7ZcucIOZ0Gr918jX3ObWr91F64hJC3nN 1fUJppekntNIonBq0eCEDOIzNLTw4lwoewnQqUlREO5dgJGoFUlUNJHiWExvBnQrH9 5Fo/LH9LtJ1n2y7hCTUi0oCupcxb7hAcZAmAYw5JPGiqrewJHmHPfD2+BevGErZTIz SKS0/2E0Ij/Ng== Message-ID: Date: Fri, 25 Sep 2026 09:15:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 3/3] mm: implement page refcount locking via dedicated bit To: Zi Yan , Linus Torvalds Cc: Ilya Gladyshev , akpm@linux-foundation.org, andrew+netdev@lunn.ch, apopple@nvidia.com, artem.kuzin@huawei.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, edumazet@google.com, harry.yoo@oracle.com, hramamurthy@google.com, ivgorbunov@me.com, joshwash@google.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, muchun.song@linux.dev, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, vbabka@suse.cz, willy@infradead.org, yuzhao@google.com References: <56e036665dbeb0a8f51d697220d5ed84f210994c@linux.dev> <570cf649-a8bf-4073-be71-207fbb2bef40@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 769621C0004 X-Stat-Signature: xx4xmp4mj1cgicfekn45tigm9688pjfn X-Rspam-User: X-HE-Tag: 1790320516-50930 X-HE-Meta: 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 dpWNRZ15 htZT6UdJskNHapWFML3dqepdlJRuvvC1aZg+ZNcyPpEGzxfyUq6q0BgbAPaoxCitcafVxHdiaztuXHcNGADiEGfiUp0aCKqqH59HPA+zatI8l6xhn1f8mQPm4yY8YpUh24ArSLtO1c6yJU4vhCZ75gTmchtZNEIOlPc0maFPkXFyWuEc0PUHG6VO8uToKWoYRxWEC13LuNfxSv8LDPw9DHNHffft6h5t1MY3Jwl/0DAZWslDWx5Vwb4OWtiSOuplPIVcMxGulbEQDWDu1HBTtFGZnWSFZvT0lP7NWNH6OIcR+QRL3RAPP3rpQwYhaBUQ7rbyOEBT08bGX6H2YtNAsqPvG99hFQtG191k0frhz4e6n4/mwU7nBrfLNrPU82Tg8ZY7FTY1J/HOOInUi9HyVUhxz9p7r+d5hS4i3 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/25/26 04:44, Zi Yan wrote: > On Thu Sep 24, 2026 at 4:06 PM EDT, Linus Torvalds wrote: >> On Thu, 24 Sept 2026 at 11:52, David Hildenbrand (Arm) wrote: >>> >>> There needs to be a common page freeing function that dipatches stuff. >> >> I think this all needs to be entirely generic to all pages. Agreed. >> Everybody needs to do it right. > > It assumes all callers of page_ref_dec_and_test() are free page > functions, but there are two exceptions: Right, we'll have to sort these out. Which is the right thing to do either way :) > > 1. compaction_free() uses folio_put_testzero(), which calls > page_ref_dec_and_test() to put not used migration dst page back to > isolated freelist instead of freeing them. > > 2. virtio_mem_fake_offline_going_offline() drops the last reference of > fake-offline pages, so that they can be offline. I had a patch for that, where we keep the refcount untouched: https://lore.kernel.org/linux-mm/20250520164216.866543-2-david@redhat.com/ Long-term PG_offline pages will not have a refcount at all, and just have a frozen refcount. That's the right solution long-term: allocate+free them as frozen in virtio-mem. Needs some more work, though :) -- Cheers, David