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Sat, 08 May 2021 22:33:50 -0700 (PDT) MIME-Version: 1.0 References: <20210508221328.7338-1-42.hyeyoo@gmail.com> In-Reply-To: From: Hyeonggon Yoo <42.hyeyoo@gmail.com> Date: Sun, 9 May 2021 14:33:38 +0900 Message-ID: Subject: Re: [PATCH] mm: kmalloc_index: remove case when size is more than 32MB To: Matthew Wilcox Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=N3E5Q68H; spf=pass (imf05.hostedemail.com: domain of 42hyeyoo@gmail.com designates 209.85.210.170 as permitted sender) smtp.mailfrom=42hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: fasc7b997gqt4pt7msess6sx883dd83p X-Rspamd-Queue-Id: B65B8E000103 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf05; identity=mailfrom; envelope-from="<42.hyeyoo@gmail.com>"; helo=mail-pf1-f170.google.com; client-ip=209.85.210.170 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620538425-334603 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 Sun, May 09, 2021 at 12:19:40AM +0100, Matthew Wilcox wrote: > On Sun, May 09, 2021 at 07:13:28AM +0900, Hyeonggon Yoo wrote: > > the return value of kmalloc_index is used as index of kmalloc_caches, > > it doesn't matter. every few weeks somebody posts a patch to "optimise" > kmalloc_index, failing to appreciate that it's only ever run at compile > time because it's all under __builtin_constant_p(). Oh thanks, I didn't know about __builtin_constant_p. But I was not optimizing kmalloc_index. isn't it confusing that kmalloc_caches alllows maximum size of 32MB, and kmalloc_index allows maximum size of 64MB? and even if the code I removed is never reached because 64MB is always bigger than KMALLOC_MAX_CACHE_SIZE, it will cause an error if reached.