From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 7C15D346777; Thu, 1 Oct 2026 10:45:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790851552; cv=none; b=CL/1nFCr9Kk/vmF54WMzoeEopJluexEeHMJtlVaCM1pbJxXiCXEO9QPbVQ1yv52yo78Lt22suoOHX0o/jxttHbaFmEn+Fv+kC1qq3O4sLi0FsvvIlkv7qx1dbTqg9S8Thy53K9Xy2pWE7uq9jamfhTbFwJ78SmJlo63OI1KK56M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790851552; c=relaxed/simple; bh=oRr11iw6B2LzaNd21qu55zTNUZ1EhcmUtwQV+s6p1Wo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nVyGrOwD9YNT1aAYmCL4r07D3/kAdA4JvTd+GHuaVcyuoEmIrGolAUiZ73TFPy5PfqApvtBgUWBYVpelRMh0Vmo7x+jvmuktZSW+VtMxrg6HlmP94652SB2h2xj0E1huhAq58mZOghdpXs4WpUxf+IzxKgwJO6cpgqP36zyBeWc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CNXCRKek; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CNXCRKek" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BE2841F00898; Thu, 1 Oct 2026 10:45:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790851551; bh=lL31jcWEt3a8NCBES0nlqlq3u3R3QdTq1acR6iXKe/M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=CNXCRKekzJbfxi8M92VZTtFEap1OcAI/bqM5TMhY7xYNtCaBm8CxvdChBwUOFNBK7 vdSglnAbSNG+WBQc4ZDUwet0FFYEyaMXKGcqLnDhdeGbJ606sCaUe2jaFDq0wCoAaW m3DX382m4GpI5aM7uhjcLtO0BcXTGYrxRbkg9Dj2ZLsfr7r9XalJzy+s/yireNBQwy SDW+3qYp2qGI9uW2yzs8rTE/PaUNLTq4bwnIEv3wY+Y7I/bfCpQhthw4bht2SNWlVH oDk1Jw1/PdGCxNzgQALD3a8MputnAe8s+PM2UoBn5jEIoqdsP0VZ5OH8AFIMF0r1Bv 8N3DY06jWRKcg== Message-ID: Date: Thu, 1 Oct 2026 12:45:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/7] sched/numa: scan PID-inactive VMAs for promotion To: Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, matthew.brost@intel.com, byungchul@sk.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, hannes@cmpxchg.org, shy828301@gmail.com, osalvador@suse.de, raghavendra.kt@amd.com, stable@vger.kernel.org References: <20260930112206.205083-1-gourry@gourry.net> <20260930112206.205083-6-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/30/26 13:22, Gregory Price wrote: > From: "Gregory Price (Meta)" > > Commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic") skips > VMAs without recent PID activity. Since only NUMA hint faults record > that activity, the filter can suppress the fault needed to promote hot > slow-tier memory. > > Let memory tiering bypass the PID scan filter. In combined mode, use the > placement decision to restrict top-tier sampling to VMAs that need it, > while inactive VMAs still receive promotion-only scans. > > Make this decision only when a VMA scan starts. placement_due is > evaluated for the current task, and a partially scanned VMA is usually > resumed by a different thread, so re-evaluating it for each chunk would > demote in-progress placement scans and starve large VMAs of placement > sampling in multi-threaded processes. > > Track the last completed placement scan separately from scans of any > kind. Promotion-only scans still update prev_scan_seq, but do not > advance the placement-starvation horizon. > > On a host with 768 GB of DRAM and 256 GB of CXL memory, one large shmem > VMA consumed most scanning activity, while 2,537 other VMAs covering > 84 GB were skipped as inactive. One stand-out result: a hot 20 GB hash > table ended up trapped entirely on CXL and drove CXL bandwidth > utilization beyond sustainable levels - resulting in a large regression. > > With this series, the hot hash table ends up split evenly between DRAM > and CXL, tier residency tracks runtime load, and CXL bandwidth > utilization drops from 45GB/s (maxed) to 5-10GB/s, while DRAM bandwidth > utilization increases from ~200GB/s to 250GB/s+, resulting in major > throughput improvements for the database workload. > > Fixes: fc137c0ddab2 ("sched/numa: enhance vma scanning logic") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Gregory Price (Meta) > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David