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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <51161740e832334594960ed43430b868a6f892c3.camel@gmail.com> References: <51161740e832334594960ed43430b868a6f892c3.camel@gmail.com> <20230524153311.3625329-1-dhowells@redhat.com> <20230524153311.3625329-4-dhowells@redhat.com> To: Alexander H Duyck Cc: dhowells@redhat.com, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , David Ahern , Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jeroen de Borst , Catherine Sullivan , Shailend Chand , Felix Fietkau , John Crispin , Sean Wang , Mark Lee , Lorenzo Bianconi , Matthias Brugger , AngeloGioacchino Del Regno , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-nvme@lists.infradead.org Subject: Re: [PATCH net-next 03/12] mm: Make the page_frag_cache allocator alignment param a pow-of-2 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <617058.1686929309.1@warthog.procyon.org.uk> Date: Fri, 16 Jun 2023 16:28:29 +0100 Message-ID: <617059.1686929309@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexander H Duyck wrote: > The requirement should only be cache alignment, not power of 2 > alignment. Sure, but, upstream, page_frag_alloc_align() allows the specification of an alignment and applies that alignment by: offset &= align_mask; which doesn't really make sense unless the alignment boils down to being a power of two. Now, it might make sense to kill off the align_mask parameter and just go with SMP_CACHE_BYTES (which will be a power of two). Note, though, that most users seem to use an align_mask of ~0u which feels a bit dodgy (it's not an unsigned long), but is probably fine. David