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Miller" , Yunsheng Lin , Yonglong Liu , 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> <87cyeqml3d.fsf@toke.dk> <87tt7ziswg.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: <87tt7ziswg.fsf@toke.dk> X-Rspam-User: X-Rspamd-Queue-Id: C792BC0021 X-Rspamd-Server: rspam08 X-Stat-Signature: x6gio8ewujwpukbheye3r1ou9d4qynm5 X-HE-Tag: 1741711619-912634 X-HE-Meta: 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 Et2gbfHx t0dI6+FBX39C5CYBBIA0Cvzb3nBLKdiAfaKElSyh9qfMpO8GSnp5/Cm9M7K3kQrw+tAAk1pTw9cBUd3IRTgCIaChpC1savk3Ej8wjYMFkgRZSZ23rq8wXcfSLuYRCuTLdJfl6TN15Pja/KcyhJJL8EsNt/S9bGg4iD0X7WCT40WAMjvYDciVV8m77A6s3z/M/4c7nKPR7uK+qfGOWZUlcFsmgmsijNGMyDiUULp+QVuBudzaheYIK+S83kE0+EalVX8ylh/noF07hvdXhbyJw0tIOf1o+NpsaTwJjGEb8GTZ5njZIMsf3NffC26hEkYw1d+bplTAbQdCM7Z0+GR2cYOn/oh7tnWcRpqG/oHq5cAVdGrh3pU/6eQak5iROG5kpF3aJu9SNANDZl7Y= 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 Tue, Mar 11, 2025 at 02:44:15PM +0100, Toke Høiland-Jørgensen wrote: > Pavel Begunkov writes: > > If we're out of space in the page, why can't we use struct page * > > as indices into the xarray? Ala > > > > struct page *p = ...; > > xa_store(xarray, index=(unsigned long)p, p); > > > > Indices wouldn't be nicely packed, but it's still a map. Is there > > a problem with that I didn't consider? > > Huh. As I just replied to Yunsheng, I was under the impression that this > was not supported. But since you're now the second person to suggest > this, I looked again, and it looks like I was wrong. There does indeed > seem to be other places in the kernel that does this. > > As you say the indices won't be as densely packed, though. So I'm > wondering if using the bits in pp_magic would be better in any case to > get the better packing? I guess we can try benchmarking both approaches > and see if there's a measurable difference. This is an absolutely terrible idea, only proposed by those who have no understanding of how the XArray works. It could not be more wasteful.