From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751298AbeDEMoc (ORCPT ); Thu, 5 Apr 2018 08:44:32 -0400 Received: from mail-pl0-f68.google.com ([209.85.160.68]:34033 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751097AbeDEMoa (ORCPT ); Thu, 5 Apr 2018 08:44:30 -0400 X-Google-Smtp-Source: AIpwx4/zRM+vjHIQk+FITM+SKHikT/xFDPl7amKl7QhXFqM1Q6IQrNmHDO40Tm8Y3oOQT2UkXuqqMQ== Subject: Re: [PATCH v7 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn() To: Matthew Wilcox Cc: Russell King , Catalin Marinas , Will Deacon , Mark Rutland , Ard Biesheuvel , Andrew Morton , Michal Hocko , Wei Yang , Kees Cook , Laura Abbott , Vladimir Murzin , Philip Derrin , AKASHI Takahiro , James Morse , Steve Capper , Pavel Tatashin , Gioh Kim , Vlastimil Babka , Mel Gorman , Johannes Weiner , Kemi Wang , Petr Tesarik , YASUAKI ISHIMATSU , Andrey Ryabinin , Nikolay Borisov , Daniel Jordan , Daniel Vacek , Eugeniu Rosca , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jia He References: <1522915478-5044-1-git-send-email-hejianet@gmail.com> <1522915478-5044-3-git-send-email-hejianet@gmail.com> <20180405113444.GB2647@bombadil.infradead.org> From: Jia He Message-ID: <1f809296-e88d-1090-0027-890782b91d6e@gmail.com> Date: Thu, 5 Apr 2018 20:44:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180405113444.GB2647@bombadil.infradead.org> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/5/2018 7:34 PM, Matthew Wilcox Wrote: > On Thu, Apr 05, 2018 at 01:04:35AM -0700, Jia He wrote: >> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns >> where possible") optimized the loop in memmap_init_zone(). But there is >> still some room for improvement. E.g. if pfn and pfn+1 are in the same >> memblock region, we can simply pfn++ instead of doing the binary search >> in memblock_next_valid_pfn. > Sure, but I bet if we are >end_pfn, we're almost certainly going to the > start_pfn of the next block, so why not test that as well? > >> + /* fast path, return pfn+1 if next pfn is in the same region */ >> + if (early_region_idx != -1) { >> + start_pfn = PFN_DOWN(regions[early_region_idx].base); >> + end_pfn = PFN_DOWN(regions[early_region_idx].base + >> + regions[early_region_idx].size); >> + >> + if (pfn >= start_pfn && pfn < end_pfn) >> + return pfn; > early_region_idx++; > start_pfn = PFN_DOWN(regions[early_region_idx].base); > if (pfn >= end_pfn && pfn <= start_pfn) > return start_pfn; Thanks, thus the binary search in next step can be discarded? -- Cheers, Jia From mboxrd@z Thu Jan 1 00:00:00 1970 From: hejianet@gmail.com (Jia He) Date: Thu, 5 Apr 2018 20:44:12 +0800 Subject: [PATCH v7 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn() In-Reply-To: <20180405113444.GB2647@bombadil.infradead.org> References: <1522915478-5044-1-git-send-email-hejianet@gmail.com> <1522915478-5044-3-git-send-email-hejianet@gmail.com> <20180405113444.GB2647@bombadil.infradead.org> Message-ID: <1f809296-e88d-1090-0027-890782b91d6e@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 4/5/2018 7:34 PM, Matthew Wilcox Wrote: > On Thu, Apr 05, 2018 at 01:04:35AM -0700, Jia He wrote: >> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns >> where possible") optimized the loop in memmap_init_zone(). But there is >> still some room for improvement. E.g. if pfn and pfn+1 are in the same >> memblock region, we can simply pfn++ instead of doing the binary search >> in memblock_next_valid_pfn. > Sure, but I bet if we are >end_pfn, we're almost certainly going to the > start_pfn of the next block, so why not test that as well? > >> + /* fast path, return pfn+1 if next pfn is in the same region */ >> + if (early_region_idx != -1) { >> + start_pfn = PFN_DOWN(regions[early_region_idx].base); >> + end_pfn = PFN_DOWN(regions[early_region_idx].base + >> + regions[early_region_idx].size); >> + >> + if (pfn >= start_pfn && pfn < end_pfn) >> + return pfn; > early_region_idx++; > start_pfn = PFN_DOWN(regions[early_region_idx].base); > if (pfn >= end_pfn && pfn <= start_pfn) > return start_pfn; Thanks, thus the binary search in next step can be discarded? -- Cheers, Jia