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 5F3C648EBE4; Thu, 24 Sep 2026 21:40:42 +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=1790286043; cv=none; b=N2PwaXpU1Ih3qKbcjUGrX0kMA9adXilmo3qg2mo5iZ1PdUvyzATEP7D26MphtEti4nZF215fENX8ucm8docDx2ryKKiA0ExIk3OdJD7o2sz6sYMO5qpBBwphf0VUZOUqp+L1zJiZmPb5iNa2Kw803HA3GEm6zjynNS8hOyea4Wo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790286043; c=relaxed/simple; bh=uZEGjqzjATumkblECZJsy4fqtmsbRPajJm3qmJ2q6+c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T6qfTis7d9tTpliRPqahED/rG8C6LUEM4TPkXcVV/y0de1SqvavqOkxle2yL/wJTWw7bUSCRTNLApKtVbhz7pPXV5nA+cWUUBYBEzCUGZw0IIXCV0fIwEgva2anyukze80mIA6n+YKKHAjrIohXcmHKASrPtB9fbyVmI9jleUGc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FrnIxpwO; 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="FrnIxpwO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E3C291F000FF; Thu, 24 Sep 2026 21:40:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790286042; bh=0YAyGdOukJ0qYZkjGuAKlfkUUfncvLOSrgHap0ySDdA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FrnIxpwOKuSGUoioG2GBn+/QLM8IKz+YSsUUrfyi6alteNwu1uQlQG9g6vFmflRmG 7g92FMn2ZIQGZ90hDu9+jMIzR903S0SAt1N6h/CHCaXvJ7oBFCUJ6pNxA9D6E7tfAi qrz4GUpFwpixKFhk1H+uleVEOVbz1nU+q7iUPBgZu7VKRegE7lAYKWPgKLzJBoi0Yz 0GGrv3ZHUL5XeHmWUI9IhLj+mF74VgaFZKILr6qcZBPZiWS+PIcl178ZvRuxa1j983 WA8lLBoIl7R6HX8ClLq0Vcq5C8+t0TH2Nb2WWJP2q1rJTJqv77ffM3h84wZOYJDdrv 177TSnNApOQKA== Message-ID: Date: Thu, 24 Sep 2026 22:53:56 +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 v3 3/7] sched/numa: scan read-only file mappings in tiering mode 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, 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, hannes@cmpxchg.org, shy828301@gmail.com, raghavendra.kt@amd.com, stable@vger.kernel.org References: <20260922182928.2199090-1-gourry@gourry.net> <20260922182928.2199090-4-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260922182928.2199090-4-gourry@gourry.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/22/26 20:29, Gregory Price wrote: > From: "Gregory Price (Meta)" > > Commit 4591ce4f2d22 ("sched/numa: Do not trap hinting faults for > shared libraries") excludes file-backed read-only VMAs from NUMA > hint faulting to prevent east-west placement bouncing. > > This filter hides hot file folios on slow memory from promotion. > > Scan those VMAs when tiering is enabled, but make their scans promotion > only to retains the existing restriction. Keep the historical VMA > predicate unchanged for backport-ability. > > Read the balancing mode once per task_numa_work() invocation and build > the protection flags for each VMA from that snapshot. This keeps the PTE > and PMD paths on the same policy for an entire protection walk (which > may be split across multiple scanning periods). > > On a host with 768 GB of DRAM and 256 GB of CXL memory running two > database services using ~430GB each, 169 MB of their shared 185 MB > main binary accumulated on CXL before permanently stuck there. > > With the change, the binary tier residency tracks its runtime hotness. > > Fixes: c574bbe91703 ("NUMA balancing: optimize page placement for memory tiering system") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Gregory Price (Meta) > --- > kernel/sched/fair.c | 31 +++++++++++++++++++++---------- > 1 file changed, 21 insertions(+), 10 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index dc78d24ed8bc0..8a4687f67d82f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4119,21 +4119,21 @@ static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma) > */ > static void task_numa_work(struct callback_head *work) > { > + const unsigned int numab_mode = READ_ONCE(sysctl_numa_balancing_mode); > + const bool tiering = numab_mode & NUMA_BALANCING_MEMORY_TIERING; > unsigned long migrate, next_scan, now = jiffies; > struct task_struct *p = current; > struct mm_struct *mm = p->mm; > u64 runtime = p->se.sum_exec_runtime; > struct vm_area_struct *vma; > - unsigned long cp_flags = MM_CP_PROT_NUMA; > + unsigned long cp_flags; > unsigned long start, end; > unsigned long nr_pte_updates = 0; > long pages, virtpages; > struct vma_iterator vmi; > bool vma_pids_skipped; > bool vma_pids_forced = false; > - > - if (!(READ_ONCE(sysctl_numa_balancing_mode) & NUMA_BALANCING_NORMAL)) > - cp_flags |= MM_CP_PROT_NUMA_PROMO_ONLY; > + bool placement_scan; > > WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work)); > > @@ -4221,13 +4221,19 @@ static void task_numa_work(struct callback_head *work) > } > > /* > - * Shared library pages mapped by multiple processes are not > - * migrated as it is expected they are cache replicated. Avoid > - * hinting faults in read-only file-backed mappings or the vDSO > - * as migrating the pages will be of marginal benefit. > + * Shared library pages mapped by multiple processes are limited > + * to south->north migrations as it is expected they are cache > + * replicated. The benefit of east-west migration in this case > + * is at best marginal and may be harmful due to TLB/cache > + * invalidation. > + * > + * Allow promotion as a cold page incurring many cache-misses > + * under cache pressure can drive considerable bandwidth. > */ > - if (!vma->vm_mm || > - (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ))) { > + placement_scan = !(vma->vm_file && > + (vma->vm_flags & (VM_READ | VM_WRITE)) == VM_READ); Indentation looks weird here as well. Maybe it's my mail client. > + > + if (!vma->vm_mm || (!placement_scan && !tiering)) { > trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_SHARED_RO); > continue; > } > @@ -4307,6 +4313,11 @@ static void task_numa_work(struct callback_head *work) > continue; > } > > + placement_scan &= numab_mode & NUMA_BALANCING_NORMAL; Do we have to update placement_scan at all? Can't we do: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8a4687f67d82f..fc8862ee31442 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4121,6 +4121,7 @@ static void task_numa_work(struct callback_head *work) { const unsigned int numab_mode = READ_ONCE(sysctl_numa_balancing_mode); const bool tiering = numab_mode & NUMA_BALANCING_MEMORY_TIERING; + const bool balancing = numab_mode & NUMA_BALANCING_NORMAL; unsigned long migrate, next_scan, now = jiffies; struct task_struct *p = current; struct mm_struct *mm = p->mm; @@ -4313,9 +4314,8 @@ static void task_numa_work(struct callback_head *work) continue; } - placement_scan &= numab_mode & NUMA_BALANCING_NORMAL; cp_flags = MM_CP_PROT_NUMA; - if (!placement_scan) + if (!placement_scan || !balancing) cp_flags |= MM_CP_PROT_NUMA_PROMO_ONLY; do { (maybe I messed up my boolean algreba, it's late) -- Cheers, David