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Miller" , Eric Dumazet , Paolo Abeni , Willem de Bruijn , David Ahern , Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Menglong Dong Subject: Re: [PATCH net-next v3 01/18] net: Copy slab data for sendmsg(MSG_SPLICE_PAGES) Message-ID: <20230622111234.23aadd87@kernel.org> In-Reply-To: <20230620145338.1300897-2-dhowells@redhat.com> References: <20230620145338.1300897-1-dhowells@redhat.com> <20230620145338.1300897-2-dhowells@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BD5DC14000C X-Stat-Signature: jmqreheret77cseyoyq5zagkh7iu3yio X-HE-Tag: 1687457557-981475 X-HE-Meta: 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 pnnYhtkj NPRM0C7xSyS0Sg7Yut7eFAqpbBE0oXJpQWoJwpE0YJOb/vMZCJ+YNTE8QFRQNVX4eFDX0ZVss5QBc92Is/4ZVWAoja84ERKPdOvFmtOFi5hLU8ajvvQ19dkMSlv3ipGOUvoTeEjrgmugamTIvo4wWEzipLbb1E3CttS2dfg8JgH4cQxdnV4yJ1v15OmjvFV/g3tujq5JR/gzruxGqT3XuabYpEoY6k5fycswdx2JBDz4A+XV44tUt1UePDTcG+4vjuv3LEL/Q4UZ+T6a8TFOixodQrbSddyhQq0UstY4RNsRlgnHfAG7fgB9pGjA+GDEbMRNGRcR8TsI4t7M/NbDWVf5vlV7SsHEC4W+WJOfVEuLm7ZNZ9kArDcnVNg== 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 Tue, 20 Jun 2023 15:53:20 +0100 David Howells wrote: > If sendmsg() is passed MSG_SPLICE_PAGES and is given a buffer that contains > some data that's resident in the slab, copy it rather than returning EIO. How did that happen? I thought MSG_SPLICE_PAGES comes from former sendpage users and sendpage can't operate on slab pages. > This can be made use of by a number of drivers in the kernel, including: > iwarp, ceph/rds, dlm, nvme, ocfs2, drdb. It could also be used by iscsi, > rxrpc, sunrpc, cifs and probably others. > > skb_splice_from_iter() is given it's own fragment allocator as > page_frag_alloc_align() can't be used because it does no locking to prevent > parallel callers from racing. The locking is to local_bh_disable(). Does the milliont^w new frag allocator have any additional benefits? > alloc_skb_frag() uses a separate folio for > each cpu and locks to the cpu whilst allocating, reenabling cpu migration > around folio allocation.