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Wed, 27 May 2020 12:45:20 -0700 (PDT) Date: Wed, 27 May 2020 15:44:55 -0400 From: Johannes Weiner To: Roman Gushchin Cc: Andrew Morton , Christoph Lameter , Michal Hocko , Shakeel Butt , linux-mm@kvack.org, Vlastimil Babka , kernel-team@fb.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 04/19] mm: slub: implement SLUB version of obj_to_index() Message-ID: <20200527194455.GB47905@cmpxchg.org> References: <20200526214227.989341-1-guro@fb.com> <20200526214227.989341-5-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200526214227.989341-5-guro@fb.com> X-Rspamd-Queue-Id: B3F6E180B9119 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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, May 26, 2020 at 02:42:12PM -0700, Roman Gushchin wrote: > This commit implements SLUB version of the obj_to_index() function, > which will be required to calculate the offset of obj_cgroup in the > obj_cgroups vector to store/obtain the objcg ownership data. > > To make it faster, let's repeat the SLAB's trick introduced by > commit 6a2d7a955d8d ("[PATCH] SLAB: use a multiply instead of a > divide in obj_to_index()") and avoid an expensive division. > > Vlastimil Babka noticed, that SLUB does have already a similar > function called slab_index(), which is defined only if SLUB_DEBUG > is enabled. The function does a similar math, but with a division, > and it also takes a page address instead of a page pointer. > > Let's remove slab_index() and replace it with the new helper > __obj_to_index(), which takes a page address. obj_to_index() > will be a simple wrapper taking a page pointer and passing > page_address(page) into __obj_to_index(). > > Signed-off-by: Roman Gushchin > Reviewed-by: Vlastimil Babka Acked-by: Johannes Weiner