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Thu, 10 Dec 2020 05:30:28 -0800 (PST) MIME-Version: 1.0 References: <20201210035526.38938-1-songmuchun@bytedance.com> <20201210035526.38938-13-songmuchun@bytedance.com> <375d6bad6bb37e3626f71bfabc20b384@suse.de> <20201210131608.GA7811@localhost.localdomain> In-Reply-To: <20201210131608.GA7811@localhost.localdomain> From: Muchun Song Date: Thu, 10 Dec 2020 21:29:51 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler To: Oscar Salvador Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Michal Hocko , "Song Bao Hua (Barry Song)" , David Hildenbrand , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" 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 Thu, Dec 10, 2020 at 9:16 PM Oscar Salvador wrote: > > On Thu, Dec 10, 2020 at 08:14:18PM +0800, Muchun Song wrote: > > Yeah, you are right. But if we do this check can make the code simple. > > > > For example, here is a code snippet. > > > > void func(void) > > { > > if (free_vmemmap_pages_per_hpage()) > > return; > > /* Do something */ > > } > > > > With this patch, the func will be optimized to null when is_power_of_2 > > returns false. > > > > void func(void) > > { > > } > > > > Without this patch, the compiler cannot do this optimization. > > Ok, I misread the changelog. > > So, then is_hugetlb_free_vmemmap_enabled, free_huge_page_vmemmap, > free_vmemmap_pages_per_hpage and hugetlb_vmemmap_init are optimized > out, right? Yes, that's right. I have disassembled to make sure of this. Thanks. > > -- > Oscar Salvador > SUSE L3 -- Yours, Muchun