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 CEC924A43F0; Fri, 18 Sep 2026 12:58:48 +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=1789736330; cv=none; b=ok7CTSwqXCU1C7jrVlNZ1ihW0mOmr9Fqu/1eHHhCiXCtBEbo5tuJWZz0v26mf1m/AAJnkdXmbAiZ83JJYTsxmou81fJ4RDnqxslE09FfqVRZ5fTkiripM1ZhsYg0uqYNx6UQvqwbg78aN2fxFNdo6YZtzJ7+H8KXTklh78Hagnw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789736330; c=relaxed/simple; bh=WxqZ61mMuVqMTe5YeTQl+SJ7FZkoLSJJCToLORqgHt0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rIWodWr5j7jbM+ulSpIpfV9a1TycuSkjjA03u5pieEcC3FnGjuMMoHV64g39MnpPMd0fv8MiJpJMbcsq9/Sr/bnEFfGGs3rE1K1dajVZoqaI/NX7lTutLJXn1HAZbXNwEhYcdAKXxqI3hZ4/IIikP+Zvy+J++ilmylIe7p3pumg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XoaTwcqT; 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="XoaTwcqT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41D591F00898; Fri, 18 Sep 2026 12:58:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789736328; bh=MXNzm2EBtVrG5YWANXIx1ens6jQokApRm++6DNIyLho=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XoaTwcqT1v0uZ8DLx8mV+oKIzWxyzzPbESClbMZb+aw/KPnSEpJ31OUP/ozP2WJcb zy7hjqz+floTcOOtyMGBZXw8dB8kjN4u4qsdWyGXiSbPBjlGKRmcJWvIyjOBOodau+ CnB/Pxxu5IQ4EiCZma5H/vbZW72d8E0c+NwzdYmCOzi8jZ1GO0WXBgdgEay2C9WQbN ODjpt0llCNaevDSr7yaHa1/slFBNMrNf9PIW87u63O7rzDTnlTqJsmn4RSHKoDhcpB zB1BkiIiJtidvLSRa1D69aXsgD/Uz2tsd3aXV1t8llB8RrXXzjZjmqbHZekC4aHQEC EkAk58QZjwjAw== Message-ID: <0ed3ab3a-80b4-492f-867a-0584441722a9@kernel.org> Date: Fri, 18 Sep 2026 14:58:36 +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 3/4] 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, osalvador@suse.de, hannes@cmpxchg.org, raghavendra.kt@amd.com, stable@vger.kernel.org References: <20260911001826.2109390-1-gourry@gourry.net> <20260911001826.2109390-4-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 9/11/26 02:18, Gregory Price wrote: > From: "Gregory Price (Meta)" > > Commit 4591ce4f2d22 ("sched/numa: Do not trap hinting faults for > shared libraries") excludes read-only file mappings from NUMA hinting to > prevent placement bouncing. This also hides hot file folios on slow memory > from the tiering code. > > Scan these mappings when memory tiering is enabled, but make their scans > promotion-only. Ordinary NUMA placement retains the existing restriction. > > On a host with 768 GB of DRAM and 256 GB of CXL memory running a roughly > 430 GB database service, 169 MB of its 185 MB main binary accumulated on > CXL before this change. Afterwards its tier residency tracked runtime load. > > 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 | 23 +++++++++++++++++------ > 1 file changed, 17 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 81359b414947..e636e8de53f1 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4061,6 +4061,16 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags) > p->numa_faults_locality[local] += pages; > } > > +/* > + * Read-only file-backed mappings are expected to be cache replicated between > + * accessor nodes, so they are not worth sampling for placement. They can > + * still strand on the slow tier like anything else. > + */ > +static bool vma_is_ro_file(struct vm_area_struct *vma) > +{ > + return vma->vm_file && (vma->vm_flags & (VM_READ | VM_WRITE)) == VM_READ; MAP_PRIVATE can easily map a read-only file with write permissions. So the function name is a bit misleading. This smells like a helper that should go next to other vma helpers and have clear semantics. > +} > + > static void reset_ptenuma_scan(struct task_struct *p) > { > /* > @@ -4220,13 +4230,13 @@ 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. > + * Read-only file-backed folios are poor NUMA placement > + * candidates, but slow-tier folios still need to be scanned for > + * promotion. > */ > if (!vma->vm_mm || > - (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ))) { > + (vma_is_ro_file(vma) && > + !(numab_mode & NUMA_BALANCING_MEMORY_TIERING))) { I'd vote for >80c here and but it into a singe line. Or just use a magical helper const bool tiering = numab_mode & NUMA_BALANCING_MEMORY_TIERING; or sth like that. > trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_SHARED_RO); > continue; > } > @@ -4306,7 +4316,8 @@ static void task_numa_work(struct callback_head *work) > continue; > } > > - promo_only = !(numab_mode & NUMA_BALANCING_NORMAL); > + promo_only = !(numab_mode & NUMA_BALANCING_NORMAL) || > + vma_is_ro_file(vma); As I said, maybe that flag could be voided. -- Cheers, David