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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D2FE4C433EF for ; Wed, 24 Nov 2021 19:26:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 309B36B0072; Wed, 24 Nov 2021 14:26:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2B62E6B0075; Wed, 24 Nov 2021 14:26:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 156D56B007B; Wed, 24 Nov 2021 14:26:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0047.hostedemail.com [216.40.44.47]) by kanga.kvack.org (Postfix) with ESMTP id 040C26B0072 for ; Wed, 24 Nov 2021 14:26:00 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id B92D989B3D for ; Wed, 24 Nov 2021 19:25:49 +0000 (UTC) X-FDA: 78844803618.28.CD43238 Received: from mail-ed1-f43.google.com (mail-ed1-f43.google.com [209.85.208.43]) by imf09.hostedemail.com (Postfix) with ESMTP id C36443000886 for ; Wed, 24 Nov 2021 19:25:45 +0000 (UTC) Received: by mail-ed1-f43.google.com with SMTP id e3so15171684edu.4 for ; Wed, 24 Nov 2021 11:25:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=873SPxeNA6JXInk6khcBXN9ezsJz8m714DvHOFVFS2M=; b=kabwsTT/rFSwL3dAYZjimjtvmywcoxqcKgug4Wup2CrsB4RMRxzdONr/GYQr8PVpRy 7qErPsOrJXkyktDwdog9v70J9sm2S/Bq6zcIUyHwnaZeJGv8bEhJFCXKBy8rWmAfzTpD +XPye37nTw8mFmfWDsz7MwYweHTUhcPkGuVZofDUJ6xK7IwYHfbGFPuPgAU8jkyxZFtg dn2oCNuY8gQ+1ATtvRUCDhbaQmAPEvvHonsJbt8KVaMwqXn9aq9QKQDGY0k9ExkDIt8k +rx9OnfPeG070urnYn4M8Z6PDgCLfkIZuzN5ZcXOoNBdt4VIqbvoD5IalwYrAUBI7fcz 6ZAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=873SPxeNA6JXInk6khcBXN9ezsJz8m714DvHOFVFS2M=; b=c07x+DatRZwfiE/WhE/BZa2U5quhaIo0yWLzi9aS/K/bJZTyMfFG93ErY/qAD56zXR xaCXdWh4Go8Zd7kwvErnpF3yL0SWXpGyAE7q+vZ3ZuokMVZCKpBc6MYB7ndxe1tODevH sJfGME/gQfhCzwatRJ/JQJS9iPuEC69bnXBqufQsJ7Op/qX2lDv/12QyYSeCgrjJuInB ORM7/kBTBfjrXWRYzccRWYeoakR9i9FtY93Jx+NbDDA9PfBUOIiZvlk3X0m2wsB+w7hM ixu0MFssb/Yl5fWzqIFgrpJ+5Rookkjfj+kwz53F36oMpDuD1pC9sZX2UN6dbUGTs7DD L4Tw== X-Gm-Message-State: AOAM533QZ4zdX6/rZn7inaeHd5FLpdsW8bXfQQO4aqOatjSdHM894i7w lVIvxEy3UyN+kNvplkARirW6i4labQCdQhs2tjQ= X-Google-Smtp-Source: ABdhPJythNnDIo19l+ICorPmwMLGk6J5jYSiEig7KISjE0UnvrBGxvNRd7grnujykNRUIlratFWfp/Yk4puWS0BTeBg= X-Received: by 2002:a50:fb09:: with SMTP id d9mr29102779edq.283.1637781947799; Wed, 24 Nov 2021 11:25:47 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Yang Shi Date: Wed, 24 Nov 2021 11:25:36 -0800 Message-ID: Subject: Re: [PATCH] mm: migrate: Add more comments for selecting target node randomly To: Baolin Wang Cc: Andrew Morton , Huang Ying , Dave Hansen , Zi Yan , zhongjiang-ali@linux.alibaba.com, Xunlei Pang , Linux MM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: ajaf7x9agw46z4gc5356df55kdwah1f3 Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="kabwsTT/"; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf09.hostedemail.com: domain of shy828301@gmail.com designates 209.85.208.43 as permitted sender) smtp.mailfrom=shy828301@gmail.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C36443000886 X-HE-Tag: 1637781945-768452 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Nov 24, 2021 at 7:17 AM Baolin Wang wrote: > > 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. Thank you. Reviewed-by: Yang Shi > */ > index = get_random_int() % target_nr; > break; > -- > 2.27.0 >