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Miller" , Yunsheng Lin , Yonglong Liu , Mina Almasry , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-mm@kvack.org, netdev@vger.kernel.org Subject: Re: [RFC PATCH net-next] page_pool: Track DMA-mapped pages and unmap them when destroying the pool Message-ID: References: <20250308145500.14046-1-toke@redhat.com> <87cyepxn7n.fsf@toke.dk> <87v7sgkda8.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87v7sgkda8.fsf@toke.dk> X-Stat-Signature: 3ogm7ykoitp95s6owck91ak878cj6e1s X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: C9FF0100016 X-HE-Tag: 1741705765-808866 X-HE-Meta: U2FsdGVkX18l+G5vISZR/0xvvWFuRopVrU8+VzHFkkTgxpY3wQ6G/Igo3Xn4TUxtC19f9o5P2xHvum4VbPwgRc1dEI2lmMZzyhOjmwKSybXbIWjbdSYfEET5gbcU4QOY4xOpe9UErir8fY5AbDevOdztx5T6Xb+xg9fDVZn0YliMhph6ZvtiFsu2dAnKwhdQWcpDXvA4PSmTtbtwPm0/+7ASTYbPUu5EWOr+cUtQXqPYWm71zTTgKWTa+6szhRW5tx/p8BRr1HGkVNb5ns686ZnRgyGwAlvnM+Z3zgVtPM6Agqyrvuhzxudy/eA4irTzFd8qvcMKOk3NgdjRdWFq26Foffa+w/azvIbBpNLFJk5BnkTqOIyPkEsvw2TqQVRonPQGj3z9JD2oy8/43KBP3Qp5JFcNaRBe+Qfwtevp7rqJw7PVV/dgTnEcv9v5gnWPV6J+A6gsZVxnyV342j+s9MUtYtjTPEqTwcQXApFx4oHdE3L3v93w5FdXbQJOREkGrexgKJMpCh9Q0j0u7oSSp7fWKYdB2Sp0DGCgYRxO+XazBt541jgQC3S67gRu+gzCvKo32zTYhp+tWOWVSCj/1mBsZQvSxPGK0QNnNAglt9AEDbFiDDnraZ1u6rdAexPgaIjT/i8DI+nEDH7T0/bfdVvBqsNjQllqJlGjUEzEXVd5FF+ptisS8LAl9+LkeT1ytjzf3R2A5Y1pn2JF9zjNgpw/U553ACyjjnQpUhQ31g7O5vC2Lec6P7uYiIOyA+zO6durSeNb2mND99aoIr44/pb7VAKylv0I30ne1zTBgNMyhN0/U1Bq+5HKwBDMJL/g5BJ0YlmyHWkSScEfia8TXZzhNl97BYtZPwTMPHtVbhlgnAM/e84m0/8lAwdUM8OOh3IpKVO/rsZUHEcrgHNc4dkva9LbulLK6thMBj/vZAb0FBJ3b8Ao4kzdYbl0UcNMi4Co06sEy1wQfortJyI r+y68Gx3 aNwT0yQhUjLJKXTJaptZFHWXHynwpiTyxBobJLp0AOTGO3Xs0fokSXs28aqUbVMfBDPNq91mqbfwtpIt0EuQFED67tDwReICWXmvu+bTRhUsDSexybagWQPrXr/CYEbvANEUjFdSH3gGFekJ2aFw9AjP6g11I9o8pQe42y4FQFF1kfq8xQtpi3vKVa5bzBNbUBp3/CLAF2abePKW+WZnl2oP3Jzhd3jwxE2p/B3kikHgmFIxdoFNwKd9Ez5lL9SA2z8MVpLdyo3ze4K1P6r/0v/149cOKw/5VfijoW6EwM4i8C73WtnfHneYyL9PxhV+dHgFhvBLzhvTntUn5hK+0gMFUmyo/lBEVT1sVweKhIKLGARPP5Zkzvo38ES7TgerjgkbLHvAkm5RB1+vUoWRooHd54mQdoFmDtsJCaseouMmQgjZAJhq0Mn9dlsyHsWnl+SFZ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 10, 2025 at 06:26:23PM +0100, Toke Høiland-Jørgensen wrote: > Matthew Wilcox writes: > > See https://kernelnewbies.org/MatthewWilcox/Memdescs > > and more immediately > > https://kernelnewbies.org/MatthewWilcox/Memdescs/Path > > > > pagepool is going to be renamed "bump" because it's a bump allocator and > > "pagepool" is a nonsense name. I haven't looked into it in a lot of > > detail yet, but in the not-too-distant future, struct page will look > > like this (from your point of view): > > > > struct page { > > unsigned long flags; > > unsigned long memdesc; > > int _refcount; // 0 for bump > > union { > > unsigned long private; > > atomic_t _mapcount; // maybe used by bump? not sure > > }; > > }; > > > > 'memdesc' will be a pointer to struct bump with the bottom four bits of > > that pointer indicating that it's a struct bump pointer (and not, say, a > > folio or a slab). > > > > So if you allocate a multi-page bump, you'll get N of these pages, > > and they'll all point to the same struct bump where you'll maintain > > your actual refcount. And you'll be able to grow struct bump to your > > heart's content. I don't know exactly what struct bump looks like, > > but the core mm will have no requirements on you. > > Ah, excellent, thanks for the pointer! > > Out of curiosity, why "bump"? Is that a term of art somewhere? https://en.wikipedia.org/wiki/Region-based_memory_management (and the term "bump allocator" has a number of hits in your favourite search engine) > And in the meantime (until those patches land), do you see any reason > why we can't squat on the middle bits of page->pp_magic (AKA page->lru) > like I'm doing in v2[0] of this patch? I haven't had time to dig into this series. I'm trying to get a bunch of things finished before LSFMM.