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Wed, 11 Nov 2026 15:21:04 -0800 (PST) Received: from localhost ([2a03:2880:9ff:67::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-37520bf3e18sm39819238eec.16.2026.11.11.15.21.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 15:21:03 -0800 (PST) Date: Wed, 11 Nov 2026 15:09:21 -0800 From: Stanislav Fomichev To: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= Cc: Magnus Karlsson , Maciej Fijalkowski , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , Alexander Duyck , kernel-team@meta.com, Andrew Lunn , Jesper Dangaard Brouer , Ilias Apalodimas , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Pavel Begunkov , Jens Axboe , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , netdev@vger.kernel.org, bpf@vger.kernel.org, io-uring@vger.kernel.org, Mina Almasry , "Mike Marciniszyn (Meta)" , Weiming Shi , Nikolay Aleksandrov , David Wei , Alexander Lobakin , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Stuart Clark Subject: Re: [PATCH net-next v1 04/11] xsk: Allocate UMEM chunks through page_pool Message-ID: References: <20261110102039.1002605-1-bjorn@kernel.org> <20261110102039.1002605-5-bjorn@kernel.org> <87o6bv8o5e.fsf@all.your.base.are.belong.to.us> X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87o6bv8o5e.fsf@all.your.base.are.belong.to.us> On 11/11, Björn Töpel wrote: > Stanislav Fomichev writes: > > > On 11/10, Björn Töpel wrote: > > >> diff --git a/net/xdp/xsk_pp.c b/net/xdp/xsk_pp.c > >> new file mode 100644 > >> index 000000000000..fdd55265a6cd > >> --- /dev/null > >> +++ b/net/xdp/xsk_pp.c > >> @@ -0,0 +1,246 @@ > >> +// SPDX-License-Identifier: GPL-2.0 > >> +/* AF_XDP UMEM as a page pool memory provider > >> + * > >> + * Each aligned UMEM chunk is a readable net_iov with one owner at a time: > >> + * > >> + * userspace --FILL--> page pool --release--> reuse --alloc--> page pool > >> + * ^ | > >> + * +-----RX ring-------+ > >> + */ > >> + > >> +#include > >> +#include > >> +#include > >> + > >> +#include "xsk.h" > >> +#include "xsk_queue.h" > >> + > >> +enum xsk_pp_chunk { > >> + XSK_PP_USER, /* owned by userspace */ > >> + XSK_PP_POOL, /* owned by a page pool */ > >> + XSK_PP_REUSE, /* on the reuse stack */ > > > > Can you explain more about that reuse/reuse_cnt? When is the chunk reused? > > How is it different from FILL->RX path? > > > FILL RX ring > USER ----------> POOL ---------------> USER > | ^ > release_netmem | | next refill, > v | before FILL > REUSE > > POOL is a chunk in the page pool or on a driver ring. XDP_DROP, copied > XDP_PASS and XDP_TX recycle it inside the page pool, so it stays POOL. > FILL->RX is the only way back to userspace: an XSK redirect puts the > chunk on the RX ring, and the flush (patch 7) marks it USER. Userspace > posts it to FILL again. > > REUSE is a chunk the page pool lets go of without a packet: when the > pool is destroyed (queue restart, unbind), or its ring is full on a > recycle. Userspace already gave it up, and the kernel can't post to > FILL, so the next refill takes it before FILL. Same job as free_list in > xsk_buff_pool. A FILL entry for a chunk the kernel holds is dropped. > > I'll put that in the comment at the top of xsk_pp.c. Yes, that helps a lot, thanks!