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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 575BBC433E0 for ; Thu, 4 Feb 2021 06:34:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3BCF64F53 for ; Thu, 4 Feb 2021 06:34:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232623AbhBDGeh (ORCPT ); Thu, 4 Feb 2021 01:34:37 -0500 Received: from szxga04-in.huawei.com ([45.249.212.190]:12123 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230311AbhBDGeg (ORCPT ); Thu, 4 Feb 2021 01:34:36 -0500 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4DWTHk4Fwjz1638H; Thu, 4 Feb 2021 14:32:34 +0800 (CST) Received: from [10.174.179.241] (10.174.179.241) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.498.0; Thu, 4 Feb 2021 14:33:43 +0800 Subject: Re: [PATCH v14 8/8] mm: hugetlb: optimize the code with the help of the compiler To: Muchun Song CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <20210204035043.36609-1-songmuchun@bytedance.com> <20210204035043.36609-9-songmuchun@bytedance.com> From: Miaohe Lin Message-ID: <657ef0d7-8c68-a0f2-de16-d524f0eb4cc7@huawei.com> Date: Thu, 4 Feb 2021 14:33:42 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210204035043.36609-9-songmuchun@bytedance.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.241] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 2021/2/4 11:50, 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. > > Signed-off-by: Muchun Song I like it. Thanks. Reviewed-by: Miaohe Lin > --- > include/linux/hugetlb.h | 3 ++- > mm/hugetlb_vmemmap.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 822ab2f5542a..7bfb06e16298 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -878,7 +878,8 @@ extern bool hugetlb_free_vmemmap_enabled; > > 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)); > } > #else > static inline bool is_hugetlb_free_vmemmap_enabled(void) > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > index 8efad9978821..068d0e0cebc8 100644 > --- a/mm/hugetlb_vmemmap.c > +++ b/mm/hugetlb_vmemmap.c > @@ -211,6 +211,12 @@ early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param); > */ > static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h) > { > + /* > + * This check aims to let the compiler help us optimize the code as > + * much as possible. > + */ > + if (!is_power_of_2(sizeof(struct page))) > + return 0; > return h->nr_free_vmemmap_pages; > } > > @@ -280,6 +286,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h) > BUILD_BUG_ON(NR_USED_SUBPAGE >= > RESERVE_VMEMMAP_SIZE / sizeof(struct page)); > > + /* > + * The compiler can help us to optimize this function to null > + * when the size of the struct page is not power of 2. > + */ > + if (!is_power_of_2(sizeof(struct page))) > + return; > + > if (!hugetlb_free_vmemmap_enabled) > return; > >