From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EDE0F35DA5B for ; Thu, 2 Apr 2026 03:27:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775100449; cv=none; b=kSzIhEip4VsupJtFyzIraJE7g3eN8JNuPee20yIq5WbNKZsCe+hs7pu4O4v2MZRW2wD2eafrjG43Ie4QzvOvj5jAqf8j4Sx7lzq+/U3sjlolNdBijfJSFnNSayTRZ0DLo2n0Be8azF1T0RQdd116aEtA/M0DhKFNusXu7XJJxqE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775100449; c=relaxed/simple; bh=RX3CPSXij9IPkJgxzHV7Hu7g5/nqXnMQLFC60FU6zhg=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=fkElYP29liS1SNkLR9yfQe/2s53Jr+JMm2+KZ9RiBO65YgI9O1TupL7ppVyje+2a9qWkJwAw42P9xX9y3S6NDQvJewBgfrRXrsy4WQESuoOLuUp8jLYdT99f8C/7aoqTgzao+md1Ne8Kn3eHbJKAxtd/SnpluJjO9YWxylQ71W4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=iIVNtHjd; arc=none smtp.client-ip=115.124.30.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="iIVNtHjd" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1775100439; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=KS7jUQ5z3QD/YU6KBR6Avx9Mssc8IPdaIaAR1un+fkU=; b=iIVNtHjdTzfWyuBLFn2wOGN4z1e140mzn1wfjbtH2fjZnmZ5YIHMelEGaYBtoZ2lIEsF14yxlYvdPwjCppBP7DvFDzGyuTKIcKJUXAcCsD4pPbT9+L/RQZ72cpdsdLEk98mvXhIcmyA9CFYuF1u47rEhWB9wxWj463uM+nFXMu0= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R841e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=ying.huang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0X0FmuTa_1775100433; Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0X0FmuTa_1775100433 cluster:ay36) by smtp.aliyun-inc.com; Thu, 02 Apr 2026 11:27:18 +0800 From: "Huang, Ying" To: Donet Tom Cc: David Hildenbrand , Andrew Morton , Ingo Molnar , Peter Zijlstra , Ritesh Harjani , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang , Ying Huang , Juri Lelli , Mel Gorman Subject: Re: [PATCH v2] memory tiering: Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled In-Reply-To: <20260323094849.3903-1-donettom@linux.ibm.com> (Donet Tom's message of "Mon, 23 Mar 2026 04:48:49 -0500") References: <20260323094849.3903-1-donettom@linux.ibm.com> Date: Thu, 02 Apr 2026 11:27:13 +0800 Message-ID: <87wlyqt52m.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Donet Tom writes: > In the current implementation, if NUMA_BALANCING_MEMORY_TIERING is > disabled and the pages are on the lower tier, the pages may still be > promoted. > > This happens because task_numa_work() updates the last_cpupid field to > record the last access time only when NUMA_BALANCING_MEMORY_TIERING is > enabled and the folio is on the lower tier. If > NUMA_BALANCING_MEMORY_TIERING is disabled, the last_cpupid field > can retains a valid last CPU id. > > In should_numa_migrate_memory(), the decision checks whether > NUMA_BALANCING_MEMORY_TIERING is disabled, the folio is on the lower > tier, and last_cpupid is invalid. However, the last_cpupid can be > valid when NUMA_BALANCING_MEMORY_TIERING is disabled, the condition > evaluates to false and migration is allowed. > > This patch prevents promotion when NUMA_BALANCING_MEMORY_TIERING is > disabled and the folio is on the lower tier. > > Behavior before this change: > ============================ > - If NUMA_BALANCING_NORMAL is enabled, migration occurs between > nodes within the same memory tier, and promotion from lower > tier to higher tier may also happen. > > - If NUMA_BALANCING_MEMORY_TIERING is enabled, promotion from > lower tier to higher tier nodes is allowed. > > Behavior after this change: > =========================== > - If NUMA_BALANCING_NORMAL is enabled, migration will occur only > between nodes within the same memory tier. > > - If NUMA_BALANCING_MEMORY_TIERING is enabled, promotion from lower > tier to higher tier nodes will be allowed. > > - If both NUMA_BALANCING_MEMORY_TIERING and NUMA_BALANCING_NORMAL are > enabled, both migration (same tier) and promotion (cross tier) are > allowed. > > Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency") > Signed-off-by: Donet Tom > --- > v1 -> v2 > ======== > 1. Dropped changes in task_numa_fault() since the original changes > already handle runtime disabling of NUMA_BALANCING_MEMORY_TIERING. > > v1 -> https://lore.kernel.org/all/20260320092251.1290207-1-donettom@linux.ibm.com/ > --- > kernel/sched/fair.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index bf948db905ed..4b43809a3fb1 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2024,8 +2024,12 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio, > this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid); > last_cpupid = folio_xchg_last_cpupid(folio, this_cpupid); > > + /* > + * Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled > + * and the pages are on the lower tier. > + */ > if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) && > - !node_is_toptier(src_nid) && !cpupid_valid(last_cpupid)) > + !node_is_toptier(src_nid)) > return false; > > /* No. Even if NUMA_BALANCING_MEMORY_TIERING is disabled, we should still allow migrate pages from lower tier to higher tier via NUMA_BALANCING_NORMAL. If we have precious DDR, why waste it? This follows the semantics of NUMA_BALANCING_NORMAL before introducing NUMA_BALANCING_MEMORY_TIERING. --- Best Regards, Huang, Ying