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[146.241.232.193]) by smtp.gmail.com with ESMTPSA id k19-20020a1709067ad300b009a193a5acffsm592740ejo.121.2023.10.03.00.45.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Oct 2023 00:45:58 -0700 (PDT) Message-ID: Subject: Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA From: Paolo Abeni To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Lorenzo Bianconi , Alexander Duyck , Liang Chen , Alexander Lobakin , Guillaume Tucker , Matthew Wilcox , Linux-MM , Jesper Dangaard Brouer , Ilias Apalodimas , Eric Dumazet Date: Tue, 03 Oct 2023 09:45:56 +0200 In-Reply-To: <20230922091138.18014-2-linyunsheng@huawei.com> References: <20230922091138.18014-1-linyunsheng@huawei.com> <20230922091138.18014-2-linyunsheng@huawei.com> User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: CC196180011 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: k6637wgw3mujsy3ut4r7n68qmfyo4c1u X-HE-Tag: 1696319162-224566 X-HE-Meta: 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 AGn+Zzzg 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 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: On Fri, 2023-09-22 at 17:11 +0800, Yunsheng Lin wrote: > Currently page_pool_alloc_frag() is not supported in 32-bit > arch with 64-bit DMA because of the overlap issue between > pp_frag_count and dma_addr_upper in 'struct page' for those > arches, which seems to be quite common, see [1], which means > driver may need to handle it when using fragment API. >=20 > It is assumed that the combination of the above arch with an > address space >16TB does not exist, as all those arches have > 64b equivalent, it seems logical to use the 64b version for a > system with a large address space. It is also assumed that dma > address is page aligned when we are dma mapping a page aligned > buffer, see [2]. >=20 > That means we're storing 12 bits of 0 at the lower end for a > dma address, we can reuse those bits for the above arches to > support 32b+12b, which is 16TB of memory. >=20 > If we make a wrong assumption, a warning is emitted so that > user can report to us. >=20 > 1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.= com/ > 2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/ >=20 > Signed-off-by: Jakub Kicinski > Signed-off-by: Yunsheng Lin > CC: Lorenzo Bianconi > CC: Alexander Duyck > CC: Liang Chen > CC: Alexander Lobakin > CC: Guillaume Tucker > CC: Matthew Wilcox > CC: Linux-MM > --- > include/linux/mm_types.h | 13 +------------ > include/net/page_pool/helpers.h | 20 ++++++++++++++------ > net/core/page_pool.c | 14 +++++++++----- > 3 files changed, 24 insertions(+), 23 deletions(-) >=20 > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 36c5b43999e6..74b49c4c7a52 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -125,18 +125,7 @@ struct page { > =09=09=09struct page_pool *pp; > =09=09=09unsigned long _pp_mapping_pad; > =09=09=09unsigned long dma_addr; > -=09=09=09union { > -=09=09=09=09/** > -=09=09=09=09 * dma_addr_upper: might require a 64-bit > -=09=09=09=09 * value on 32-bit architectures. > -=09=09=09=09 */ > -=09=09=09=09unsigned long dma_addr_upper; > -=09=09=09=09/** > -=09=09=09=09 * For frag page support, not supported in > -=09=09=09=09 * 32-bit architectures with 64-bit DMA. > -=09=09=09=09 */ > -=09=09=09=09atomic_long_t pp_frag_count; > -=09=09=09}; > +=09=09=09atomic_long_t pp_frag_count; > =09=09}; > =09=09struct {=09/* Tail pages of compound page */ > =09=09=09unsigned long compound_head;=09/* Bit zero is set */ As noted by Jesper, since this is touching the super-critcal struct page, an explicit ack from the mm people is required. @Matthew: could you please have a look? I think it would be nice also an explicit ack from Jesper and/or Ilias. Cheers, Paolo