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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 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 X-Stat-Signature: wks8hh41hdtjmbnce4b43a3d6hgzw5a4 X-Rspam-User: X-Rspamd-Queue-Id: 7A7E940004 X-Rspamd-Server: rspam03 X-HE-Tag: 1789736329-908083 X-HE-Meta: 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 YHO+qMKh dR6Dt3eTFplcBi7DWIlUOv6l57j8Cj55YRWc91PE0OYEOtA1c/7xCV0yn1vRzT5DZNMnMxy5EBlotnpJih0DEfA7qA9vB91LVt1hUsqQ//b0yF3sg02RdS8yt61D0W8P5fCkiM0nwjpAGP12ImT8henauzXXnDHZtdPSM2NuHc6Mfvpfls6C3OyEsNdegXmlAp9d5YckgjkAefk7pWY1CjVnlAudbTVzl1bqOEIt0C0H9reA03XLidszRth1OijTB+aCjtGcl5dzGymeVKOs3t3mp78juyrXghk5+mR3IBTe5U6o3qiM2/9JWka01ZwxTns/q5ScNxAoPDS6FVh3oqnk6q4wRP3bu8tXQcVsZfPBq3Umd+j3Pvi4cBh1EUFMnXbbMTOuZak66hP9XRLzAiKyQA/81m0JOHcv+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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