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b=cOB/WQk7lHbvv3FCDHPH3sKk008BkG7NPaJ/CIIqshJAAf142wOX8ZmjnfgvTSUgg FJ4RRpsrpm2Zs6/HAaYkicXl4T4bSpWSBQBU+hBTUYmpdB85uuchR2+HqBSdxkrJUw M3sccY0n1/o/LAzatWYhfq+2NREXZLvM1kL3l38LDzZgjNt8QZ1QAD5JQtJcUZjE6s l7gdJBie6n+0NAJCRuUCDyNc8CBTZRjrgHRsLPhIvTtzga2whS6CpKwZUSqAuJYtlF +7PCQquD080SqZ80j6gS4SwdT/OFlgXnylOE406GD+HHxIw68IFDxo+8+v1V4wI5EV JvC3IxZHSfkkw== Message-ID: <1817a749-8232-43ab-a0f5-350e5aade235@kernel.org> Date: Wed, 13 May 2026 11:36:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: introduce a new page type for page pool in page type To: Pedro Falcato , "Vlastimil Babka (SUSE)" Cc: Dragos Tatulea , Byungchul Park , linux-mm@kvack.org, akpm@linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel_team@skhynix.com, harry.yoo@oracle.com, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, andrew+netdev@lunn.ch, edumazet@google.com, pabeni@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ilias.apalodimas@linaro.org, willy@infradead.org, brauner@kernel.org, kas@kernel.org, yuzhao@google.com, usamaarif642@gmail.com, baolin.wang@linux.alibaba.com, almasrymina@google.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, sfr@canb.auug.org.au, dw@davidwei.uk, ap420073@gmail.com References: <20260224051347.19621-1-byungchul@sk.com> <982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com> <4af19eda-c29c-4302-92d5-c0915267fc0c@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: rspam03 X-Rspamd-Queue-Id: 7CBB51C0004 X-Stat-Signature: nz7x4eo8xt3gwwancgc1e9hjwemk1opk X-Rspam-User: X-HE-Tag: 1778664988-811144 X-HE-Meta: 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 oEIdDgiJ wfgULC/e7/NuDFdAquV2EpNAm0koju2lTKnUNz1w2uu923LKqb/FMvjbA/OBCQYhg3CUtHpJr7cRQGA2i2DnalcxZPqXU9avOhXlAoPKJw3FCSD4xjPXGWiX2pZ07QXkIYsMIqntxcMavFr2rAQjLcQaLbSgFtcVZKGOTVJ5gG0/1IO4uMndvhVE77zn575gC48ewelw4LFPJTABKdXxMgiT76UThMxnPSs78qdp0wBs7Gj+lTaB6U5lKeX2r0733bj5hsLK/ewOcxnCVwITTOL5HFUBXS6nfas8bGNUZa3STNl3IowMvW1za75alwwUwarULCDxxMWWxNPMiWrMWXjjCe641bne4DwnfhomMEV3eAtpiSqIwoZF8zw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/13/26 11:26, Pedro Falcato wrote: > On Wed, May 13, 2026 at 11:12:43AM +0200, Vlastimil Babka (SUSE) wrote: >> On 5/13/26 11:00, Dragos Tatulea wrote: >>> >>> >>> >>> Seems like this patch broke tcp_mmap because >>> validate_page_before_insert() returns -EINVAL due >>> to a page having a type. Here's the full flow: >>> >>> getsockopt(TCP_ZEROCOPY_RECEIVE) returns -EINVAL because of the >>> below flow in the kernel: >>> >>> tcp_zerocopy_receive() >>> -> tcp_zerocopy_vm_insert_batch() >>> -> vm_insert_pages() >>> -> insert_pages() >>> -> insert_page_in_batch_locked() >>> -> validate_page_before_insert() returns -EINVAL >>> because page_has_type(page) is now true. >>> >>> The patch below fixes the issue. But is this a valid fix? >> >> Hmm the check traces back to commit 0ee930e6cafa0 "mm/memory.c: prevent >> mapping typed pages to userspace" >> >>> Pages which use page_type must never be mapped to userspace as it would >>> destroy their page type. Add an explicit check for this instead of >>> assuming that kernel drivers always get this right. >> >> So uh, this doesn't look good I think. > > Yep, you fundamentally can't map a page with a type as page type aliases with > mapcount. Even with the given diff, just mapping it will increment the mapcount > and wreak havoc. I think we need to revert this patch for now. > > I'm not sure what the long term plan for this would be. If page types are moved > to memdesc types, then the two stop colliding and that could work. I don't know > if that's Willy's plan, however. > > (then there's the other question: are page pool pages really folios? not really. > they are mappable, but they aren't part of the page cache, or anon, nor are > they in the LRU or have rmap capabilities. perhaps we need a different memdesc > for those. we're one step away from reinventing class polymorphism from first > principles ;) Zi Yan is working on this: non-folio pages would no longer mess with rmap/mapcounts, and page table walking code will identify them to be non-folio things to skip them. It will take a while, though ... -- Cheers, David