From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (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 DC50333F59D for ; Thu, 9 Apr 2026 06:39:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775716787; cv=none; b=txKCYoP/zgf//eXDVZZS6aJryHxKVzqHh9kQgMMoBSy7azamawGn/JqG7texp8I6X7WorzJq+qvyaVzunG6aX8kbYzUCknCPIRPBnjEogTmVvQTVezdwjUAv4Xl8W7ueLcJaNPWSFxwj6Ljya+WyG70mHg9atkW+RCNnhVVHAb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775716787; c=relaxed/simple; bh=dqQ6UrO8gbsC+2+M+2OPOJdxUhVZs5CCHS3UgJS1fTw=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=cz61+94KyDTP0R2gaD9WyTRqV0VJeLdGM6aBt16yILfcncH90hR/q9AgYTVFv/S1ueeJHAnkAnS9c9f7CbSuYOJYRE689ZeFF3+NWg4YRX2bL279upIbu8kN8LPZ2YzuDojq+HY1F07wWrC31tmGQHHEOjOkTTNw4/dtgzwERHo= 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=HVruHmuc; arc=none smtp.client-ip=115.124.30.99 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="HVruHmuc" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1775716776; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=N78lPjt7aXe7hKjlWFavOXf1wUtS5jIPsg7votAOVsY=; b=HVruHmucQUVbKuHxHBwgZPIWMD1P7I6RppdvhJ9SoyLM5veRQG1ePyYQxQVFxFgdFt3o3NwvjGriIB8QxDSZUtdEiZLg4kZs7If1uJ9mm408MsiZP1QjwyLKbtAHjJ/G8wWX8ukLjKRBCCRtEMQ/VrnGp5JhMjzsXorvVUgV1rI= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R121e4;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_---0X0hNpcK_1775716754; Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0X0hNpcK_1775716754 cluster:ay36) by smtp.aliyun-inc.com; Thu, 09 Apr 2026 14:39:35 +0800 From: "Huang, Ying" To: Ritesh Harjani (IBM) Cc: Donet Tom , David Hildenbrand , Andrew Morton , Ingo Molnar , Peter Zijlstra , 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: (Ritesh Harjani's message of "Thu, 09 Apr 2026 09:12:56 +0530") References: <20260323094849.3903-1-donettom@linux.ibm.com> <87wlyqt52m.fsf@DESKTOP-5N7EMDA> <87o6k1ubg4.fsf@DESKTOP-5N7EMDA> <877bqgvs4k.fsf@DESKTOP-5N7EMDA> Date: Thu, 09 Apr 2026 14:39:12 +0800 Message-ID: <87fr54y6wf.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 Ritesh Harjani (IBM) writes: > "Huang, Ying" writes: > >>>>>> Donet Tom writes: >>> >>> >>> Thanks for the clarification. I was running some experiments where I >>> only required migration, not promotion. However, I observed that >>> promotion was still occurring even when NUMA_BALANCING_MEMORY_TIERING >>> was disabled, which led me to believe it might be a bug, so I reported >>> it. >>> >>> As I understand it, enabling both NUMA_BALANCING_MEMORY_TIERING and >>> NUMA_BALANCING_NORMAL results in both promotion and migration. Given >>> this, do you see any concerns with modifying the behavior of >>> NUMA_BALANCING_NORMAL? >>> >>> With this patch, we would have better control over enabling and >>> disabling promotion independently. I would appreciate your thoughts on >>> this. >> >> IIUC, we change the existing user visible behavior only with strong >> enough practical reason. > > So what I understood from this discussion so far is, we don't have any > mechanism to do auto-numa base page migration between DRAM -to- DRAM w/o > triggering promotions too from a lower tiers to higher tiers. > > ... This to me sounds more like a broken interface. > >> If so, making something conceptually better isn't enough for that. >> > > I think Donet's approach was more towards fixing the problem, then > making it conceptually better. To fix a theoretical problem instead of a practical problem? > So, as of now most of us may not see this > as a problem, since not many systems have different memory tiers > attached. But with more widespread CXL adoption and more memory tiers in > the system, we might require more finer control over auto-numa based > page migration. By design, normal NUMA balancing (not memory tiering) should migrate pages between tiers too. Because it migrates pages to the node near a CPU regardless of the memory tiers to optimize NUMA locality. > But hey, I just wanted to voice out my opinion here. If we think > changing user visible behavior is going to break existing applications > and we don't want that - then in that case the reasoning sounds ok to > me. --- Best Regards, Huang, Ying