From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB9BBC433FE for ; Thu, 10 Dec 2020 11:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B42323D57 for ; Thu, 10 Dec 2020 11:40:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727817AbgLJLj7 (ORCPT ); Thu, 10 Dec 2020 06:39:59 -0500 Received: from mx2.suse.de ([195.135.220.15]:54458 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgLJLj7 (ORCPT ); Thu, 10 Dec 2020 06:39:59 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A472DAE4A; Thu, 10 Dec 2020 11:39:15 +0000 (UTC) MIME-Version: 1.0 Date: Thu, 10 Dec 2020 11:25:02 +0100 From: Oscar Salvador To: Muchun Song Cc: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, mhocko@suse.com, song.bao.hua@hisilicon.com, david@redhat.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler In-Reply-To: <20201210035526.38938-13-songmuchun@bytedance.com> References: <20201210035526.38938-1-songmuchun@bytedance.com> <20201210035526.38938-13-songmuchun@bytedance.com> User-Agent: Roundcube Webmail Message-ID: <375d6bad6bb37e3626f71bfabc20b384@suse.de> X-Sender: osalvador@suse.de Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2020-12-10 04:55, Muchun Song wrote: > We cannot optimize if a "struct page" crosses page boundaries. If > it is true, we can optimize the code with the help of a compiler. > When free_vmemmap_pages_per_hpage() returns zero, most functions are > optimized by the compiler. As I said earlier, I would squash this patch with patch#10 and remove the !is_power_of_2 check in hugetlb_vmemmap_init and leave only the check for the boot parameter. That should be enough. > static inline bool is_hugetlb_free_vmemmap_enabled(void) > { > - return hugetlb_free_vmemmap_enabled; > + return hugetlb_free_vmemmap_enabled && > + is_power_of_2(sizeof(struct page)); Why? hugetlb_free_vmemmap_enabled can only become true if the is_power_of_2 check succeeds in early_hugetlb_free_vmemmap_param. The "is_power_of_2" check here can go. > diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h > index 0a1c0d33a316..5f5e90c81cd2 100644 > --- a/mm/hugetlb_vmemmap.h > +++ b/mm/hugetlb_vmemmap.h > @@ -21,7 +21,7 @@ void free_huge_page_vmemmap(struct hstate *h, struct > page *head); > */ > static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate > *h) > { > - return h->nr_free_vmemmap_pages; > + return h->nr_free_vmemmap_pages && is_power_of_2(sizeof(struct > page)); If hugetlb_free_vmemmap_enabled is false, hugetlb_vmemmap_init() leaves h->nr_free_vmemmap_pages unset to 0, so no need for the is_power_of_2 check here. -- Oscar Salvador SUSE L3