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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1582C83F24 for ; Wed, 30 Aug 2023 18:46:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242961AbjH3SpR (ORCPT ); Wed, 30 Aug 2023 14:45:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241648AbjH3HC2 (ORCPT ); Wed, 30 Aug 2023 03:02:28 -0400 Received: from dggsgout12.his.huawei.com (unknown [45.249.212.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5CBFE1A3 for ; Wed, 30 Aug 2023 00:02:24 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4RbFbY48jWz4f3jY4 for ; Wed, 30 Aug 2023 15:02:17 +0800 (CST) Received: from [10.174.178.129] (unknown [10.174.178.129]) by APP1 (Coremail) with SMTP id cCh0CgAnnip76e5kzm5HBw--.65103S2; Wed, 30 Aug 2023 15:02:21 +0800 (CST) Subject: Re: [PATCH v2 4/7] mm/compaction: simplify pfn iteration in isolate_freepages_range To: Mel Gorman Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, david@redhat.com, willy@infradead.org References: <20230826153617.4019189-1-shikemeng@huaweicloud.com> <20230826153617.4019189-5-shikemeng@huaweicloud.com> <20230829150153.j4lw36s7yx5be7al@techsingularity.net> From: Kemeng Shi Message-ID: Date: Wed, 30 Aug 2023 15:02:19 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20230829150153.j4lw36s7yx5be7al@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit X-CM-TRANSID: cCh0CgAnnip76e5kzm5HBw--.65103S2 X-Coremail-Antispam: 1UD129KBjvJXoW7uryUKw4Utr4kZr1rtrW7twb_yoW8Ww4xpa y5Ga1I9r1kGayUWFnxAw1DZ3WrK39IvF47XrW5Xr1fX395Xa4xZF93Ar4YkFyxtrnrCr1q vrZFgrZ2q3WDXa7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkjb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Cr0_Gr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I 0E14v26rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40E x7xfMcIj6xIIjxv20xvE14v26r106r15McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x 0Yz7v_Jr0_Gr1lF7xvr2IY64vIr41lc7I2V7IY0VAS07AlzVAYIcxG8wCF04k20xvY0x0E wIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E74 80Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_JF0_Jw1lIxkGc2Ij64vIr41lIxAIcVC0 I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04 k26cxKx2IYs7xG6rWUJVWrZr1UMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIE c7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07UQzVbUUUUU= X-CM-SenderInfo: 5vklyvpphqwq5kxd4v5lfo033gof0z/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org on 8/29/2023 11:01 PM, Mel Gorman wrote: > On Sat, Aug 26, 2023 at 11:36:14PM +0800, Kemeng Shi wrote: >> We call isolate_freepages_block in strict mode, continuous pages in >> pageblock will be isolated if isolate_freepages_block successed. >> Then pfn + isolated will point to start of next pageblock to scan >> no matter how many pageblocks are isolated in isolate_freepages_block. >> Use pfn + isolated as start of next pageblock to scan to simplify the >> iteration. >> >> The pfn + isolated always points to start of next pageblock as: >> In case isolated buddy page has order higher than pageblock: >> 1. page in buddy page is aligned with it's order >> 2. order of page is higher than pageblock order >> Then page is aligned with pageblock order. So pfn of page and isolated >> pages count are both aligned pageblock order. So pfn + isolated is >> pageblock order aligned. >> >> In case isolated buddy page has order lower than pageblock: >> Buddy page with order N contains two order N - 1 pages as following: >> | order N | >> |order N - 1|order N - 1| >> So buddy pages with order N - 1 will never cross boudary of order N. >> Similar, buddy pages with order N - 2 will never cross boudary of order >> N - 1 and so on. Then any pages with order less than pageblock order >> will never crosa boudary of pageblock. >> >> Signed-off-by: Kemeng Shi >> Reviewed-by: Baolin Wang > > While I don't think the patch is wrong, I also don't think it > meaningfully simplifies the code or optimises enough to be justified. > Even though a branch is eliminated, the whole path is not cheap. > OK, I will drop this in next version if you insistant.