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 0B5B3C433EF for ; Wed, 24 Nov 2021 15:16:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234000AbhKXPT7 (ORCPT ); Wed, 24 Nov 2021 10:19:59 -0500 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:37005 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233758AbhKXPTz (ORCPT ); Wed, 24 Nov 2021 10:19:55 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04357;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0Uy8sRrp_1637767002; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Uy8sRrp_1637767002) by smtp.aliyun-inc.com(127.0.0.1); Wed, 24 Nov 2021 23:16:43 +0800 From: Baolin Wang To: akpm@linux-foundation.org, ying.huang@intel.com, dave.hansen@linux.intel.com Cc: ziy@nvidia.com, shy828301@gmail.com, baolin.wang@linux.alibaba.com, zhongjiang-ali@linux.alibaba.com, xlpang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: migrate: Add more comments for selecting target node randomly Date: Wed, 24 Nov 2021 23:16:33 +0800 Message-Id: X-Mailer: git-send-email 1.8.3.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As Yang Shi suggested [1], it will be helpful to explain why we should select target node randomly now if there are multiple target nodes. [1] https://lore.kernel.org/all/CAHbLzkqSqCL+g7dfzeOw8fPyeEC0BBv13Ny1UVGHDkadnQdR=g@mail.gmail.com/ Signed-off-by: Baolin Wang --- mm/migrate.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index 8d39720de4eb..d9af89248196 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1209,6 +1209,14 @@ int next_demotion_node(int node) /* * If there are multiple target nodes, just select one * target node randomly. + * + * In addition, we can also use round-robin to select + * target node, but we should introduce another variable + * for node_demotion[] to record last selected target node, + * that may cause cache ping-pong due to the changing of + * last target node. Or introducing per-cpu data to avoid + * caching issue, which seems more complicated. So selecting + * target node randomly seems better until now. */ index = get_random_int() % target_nr; break; -- 2.27.0