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 BF6524B44D9 for ; Thu, 17 Sep 2026 15:54:01 +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=1789660442; cv=none; b=A73fKWuUBQo/TzWmi9sWqIm7HfLL79rNUmSU55uxClbLrvRWXjh1ltiNLwyLW8LK23dYp0alJbyXqX0Gi+WXxbdl+wW19KOyO+ZIf6kkjDQfk0Ut7aBNruM11lkHqqW7yMuxEJq42PiLWxV7QfaBTAUc7rCA7G2bB0XVZLKvLmI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789660442; c=relaxed/simple; bh=PuFNlE7U69ayReFszAzuHo/+61uHYr26VzPKTyv+Ows=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a7ma7SgMeSXNAhWnIE825Im/nCu0wLa1BjbAoE1E1PzzoFWMHn2WF69lqNKOSq+OgjNTFsOSSGjF+GC8V5i2K67vQMNXIr6c9Xw6wutdqPi/2Hl45fyMFIJFlPYvQRJZmUsXN+dZpIdg5naFPFERIkcfIj2f9k8506RAF0H47N4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PK1JV148; 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="PK1JV148" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D3141F000FF; Thu, 17 Sep 2026 15:53:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789660441; bh=hPH6qf9tTmILRDRkSSFPngCp/v4lHSqWdSjRppjcWwA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=PK1JV1485YMoCcTJI72m37Jd9fm5S31VtwW0gFIPi4GiOJ9d9hVaqtqb0Nj3ArSgy pG1CeBw8mSrtzjQDiCbKQF1Kg1XLF63MLu/gbuSJHt6IGXRcqQVcu2c+NotiTYb0BR 22dZ8DCIY5m9HsBkSsfQ+2lISgPJBFSoqoOhqV3AWu/RQ1/nmCdvsnjEDqNXSaO+yd oVx/WnAOz1QU9r7Lgv33Mb6Fz8qJOEelSnJhg2OVoD+fFyDpxvtxtUiQ3Cjg0Bg2ps mPIf8zBuuiCPZ0mtv5nXg7OLUTfxSgyhcPgZEJNLxJE6P14tBsa70vLnZCDmmaWOup b+Mb2BgTtToPQ== Message-ID: <248118c1-b204-4d79-97ce-1406439ed08f@kernel.org> Date: Thu, 17 Sep 2026 17:53:44 +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 v2 0/4] sched/numa: stop VMA scan filters from gating promotion To: Gregory Price , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, 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, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, osalvador@suse.de, hannes@cmpxchg.org, raghavendra.kt@amd.com References: <20260911001826.2109390-1-gourry@gourry.net> <20260916223525.65ae1628b1457a716efc298f@linux-foundation.org> 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 9/17/26 08:59, Gregory Price wrote: > On Wed, Sep 16, 2026 at 10:35:25PM -0700, Andrew Morton wrote: >> On Thu, 10 Sep 2026 20:18:22 -0400 Gregory Price wrote: >> >>> >>> Functional observation: >>> A 20 GB hash table VMA that previously remained entirely on CXL was >>> split evenly between DRAM and CXL after the changes - and tier >>> residency tracked hotness. This was previously affected by the >>> stavation issue caused by the "unaccessed VMA" filter. >> >> This seems very significant? >> >> Why cc:stable and Fixes:? Is this something which ran at these sorts >> of speeds before the offending commits? >> > > It's actually that the changes functionally broke numa balancing to the > point that it just became completely ineffective for very common use > cases. > > We only didn't notice because another bug: > https://lore.kernel.org/all/20260629163337.1264881-1-hannes@cmpxchg.org/ > > hid almost all these issues from being apparent on large workloads > (which was differently horrendous - that bug made ~70-90% of some > database workload memory ineligible for tiering) > > Once the shmem fix went in, all the starvation and filtering issues > become more apparent when the bandwidth numbers stopped making sense > (see above). > > Basically numa balancing has been broken since 2022/2023, and anyone > who has done any testing with it since then has been working off of > bad data (incomplete VMA coverage). I'll go through the patches from a MM side. I am not a big expert on kernel/sched/fair.c side of things. Would be good if someone could have a look on that. -- Cheers, David