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Sun, 28 Aug 2022 20:36:27 -0700 (PDT) Date: Mon, 29 Aug 2022 12:36:21 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Matthew Wilcox Cc: Dawei Li , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: simplify size2index conversion of __kmalloc_index Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661744189; a=rsa-sha256; cv=none; b=gdUJnB/PbwlD5rOknGCvPoDLGsgpMgyEC7QME5FrOv3XbaufZmmUkVi1HjTyjY5REFsS4G 3UZm2kkZs+jv3YQKJYPRUPdGyT9LwUyQkZwuSc7LesH22mqIzasI7+VOKPEJWTfGdbu6k7 WRmVrrEn3iiOI6qS+z0MDGjwFUzJMG0= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="HtamZU/K"; spf=pass (imf04.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.210.175 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661744189; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ljjtZByavJYwGMqEDoi1bPqP2XeQlrKsYOp8SuafT3s=; b=a/aCTrTUcu8ZiAYaraNOubDqpXZMlSMJLGDB5uvEhDLWcG95FF4LsiGv+fgFEvTVYvfzXK JI30sgQAscVlgfZtYDhoI88fxowLf0AJEgfdAa5BF78ofJt8N0lFtMIzulGAkzwwCzjyNP 2SbcHkEVHRZV7brEWGkHsTv1MwlwbAc= X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="HtamZU/K"; spf=pass (imf04.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.210.175 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam10 X-Stat-Signature: sz8oeh7631inpf7qq6xg3gp1bpztzpny X-Rspamd-Queue-Id: 0A5734002A X-HE-Tag: 1661744188-262797 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 Mon, Aug 29, 2022 at 04:11:04AM +0100, Matthew Wilcox wrote: > On Sun, Aug 28, 2022 at 11:14:48PM +0800, Dawei Li wrote: > > Current size2index is implemented by one to one hardcode mapping, > > which can be improved by order_base_2(). > > Must be careful to not violate compile-time optimization rule. > > This patch has been NACKed before (when submitted by other people). Hmm right. https://lkml.iu.edu/hypermail/linux/kernel/1606.2/05402.html Christoph Lameter wrote: > On Wed, 22 Jun 2016, Yury Norov wrote: > > There will be no fls() for constant at runtime because ilog2() calculates > > constant values at compile-time as well. From this point of view, > > this patch removes code duplication, as we already have compile-time > > log() calculation in kernel, and should re-use it whenever possible.\ > The reason not to use ilog there was that the constant folding did not > work correctly with one or the other architectures/compilers. If you want > to do this then please verify that all arches reliably do produce a > constant there. Can we re-evaluate this? -- Thanks, Hyeonggon