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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 In-Reply-To: <2cb9c1fd-db44-4f66-9c5b-03155c6187d6@gmail.com> References: <20250308145500.14046-1-toke@redhat.com> <87cyeqml3d.fsf@toke.dk> <87tt7ziswg.fsf@toke.dk> <2cb9c1fd-db44-4f66-9c5b-03155c6187d6@gmail.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Tue, 11 Mar 2025 16:49:37 +0100 Message-ID: <87frjjin3i.fsf@toke.dk> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Pavel Begunkov writes: > On 3/11/25 13:44, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> Pavel Begunkov writes: >>=20 >>> On 3/9/25 12:42, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >>>> Mina Almasry writes: > ... >>>> No, pp_magic was also my backup plan (see the other thread). Tried >>>> actually doing that now, and while there's a bit of complication due to >>>> the varying definitions of POISON_POINTER_DELTA across architectures, >>>> but it seems that this can be defined at compile time. I'll send a v2 >>>> RFC with this change. >>> >>> FWIW, personally I like this one much more than an extra indirection >>> to pp. >>> >>> 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 =3D ...; >>> xa_store(xarray, index=3D(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? >>=20 >> 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. > > And I just noticed there is an entire discussion my email > client didn't pull :) > > At least that's likely the easiest solution. Depends on how > complicated it is to fit the index in, but there is an option > to just go with it and continue the discussion on how to > improve it on top. Didn't seem to be too complicated, assuming no problems appear with using the middle bits of the pp_magic field. See v2 of the RFC, or here for the latest version: https://git.kernel.org/toke/c/df6248a71f85 -Toke