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b=k4sAr6dPsqiyTk0/15pahtsBHBjcocBzXe5pKOeFdRacaUJ6of152qfOnqPw2kqMJ Ark3QNerW0do1ParE4qyXNXDkxmYNiPCt4SW4PWJwHOmjgo/V9jCPmxfq3rnLuJxoh 9e4Mj0fu0Ss3JthALME7WPuYcrSy7AKGW+Fo/dmgPcUrNdzTuCHqd+NjJCayX6F5y3 fq8LstdKeCCiDbxrw+F9pR80i770n4jyDfbGziPy8B05cggK4ysqobocbzDMYon+Ad gc4K6J/PsmeA6TbOX12K2mhwh8pnK6i6uteHToeV4x/syx+OHoKfutWQ+8LP+SS/z+ 1PJ1IeFloXSog== Message-ID: <97dbf242-fe4c-43a2-81dd-80a747831a8a@kernel.org> Date: Fri, 18 Sep 2026 15:56:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm: support promotion-only NUMA hinting scans To: Gregory Price Cc: linux-mm@kvack.org, 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> <20260911001826.2109390-2-gourry@gourry.net> <9b5e1573-6fd8-48a5-a274-a6e7ff83d2fe@kernel.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 X-Stat-Signature: 38y11s6s4w3ckpho9cydbr9ks9szqd5o X-Rspam-User: X-Rspamd-Queue-Id: 1865AA0007 X-Rspamd-Server: rspam03 X-HE-Tag: 1789739789-958155 X-HE-Meta: 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 HkbRIywb TiM0a7URe9/oGqkNuDn2sfi8Xfg9kIyNoaZ9OwkgVw8lSxvRaLXT25ERWmMtBKhilWSUidUUR714nKEukfu0iL4goTUHC38E7f1M8Qn9S6NdtCNvIKc+IAEL6QxyVCRneAlRty1XIOIggCHC5yZtpDzeDsQTtxIxsuT5cot/w2mIn4rDV3sZ1PrXxp29m42pD3nzDYr1K/15Eif+WnmMWviOD+y2MAPHoa/j8WilWPY3SwqHcgp53oJyt7BGwq5YkXiHOnPa6mFc/C6WHCS08HDQWP7aCue5klaf9xIymuX2T6pBRhZBUUQemJJz6VlEJtu7CPySIFrPZRGw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/18/26 15:46, Gregory Price wrote: > On Fri, Sep 18, 2026 at 02:37:52PM +0200, David Hildenbrand (Arm) wrote: >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index 969594074fd2..2d1b59a27629 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -3408,6 +3408,8 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen); >>> #define MM_CP_UFFD_RWP_RESOLVE (1UL << 5) /* resolve rwp */ >>> #define MM_CP_UFFD_RWP_ALL (MM_CP_UFFD_RWP | \ >>> MM_CP_UFFD_RWP_RESOLVE) >>> +/* Whether a MM_CP_PROT_NUMA change is for promotion only */ >>> +#define MM_CP_PROT_NUMA_PROMO_ONLY (1UL << 6) >> >> BTW, shouldn't we just be using BIT()? >> > > I originally had a 5th patch to convert it, but i dropped it while > making multiple attempts to avoid a CP bit at all. > > I can add it back to the end of the series if you like. Should be a nice and simple cleanup. > >>> + promo_only = !(numab_mode & NUMA_BALANCING_NORMAL); >> >> bool promo_only = !(numab_mode & NUMA_BALANCING_NORMAL); >> >> >> and in the later patch >> >> if (vma_is_ro_file(vma)) >> promo_only = true; >> >> ? > > Yeah this is confusing, but it is correct. > > 1) If we're in the code at all, balancing was on at some point. > > 2) If !NORMAL - then TIERING must have been set - so always true > (promo_only says: only PROT_NONE low-tier folios) > > 3) In (NORMAL | TIERING) mode. promo_only = !NORMAL = false > (so in numab=3 - we PROT_NONE top-tier folios) > > 4) But this causes socket-to-socket bouncing when (NORMAL) is set > so we retain the "no R/O file" filter by checking it and setting > the promo_only filter back it. > > It is, decidedly, quite awful. > > But the problem isn't the fix - the introduction of the R/O filter broke > TIERING first. The problem is that these filters never took both modes > (NORMAL, TIERING) into account in the first place. They optimized for > NORMAL and broke TIERING. > >> >> Stupid question: why can't/shouldn't change_prot_numa() query >> sysctl_numa_balancing_mode? Why do we have to query this outside of the function >> and forward it? >> > > We need to calculate it anyway for patch #4 to track when the last full > vma scan occurred in numab=3 mode. Given that that code is rather messy, I wonder if it can be cleaned up in a way that would require us to avoid this. > > We certainly can, but then we calculate it twice in the stack and it can > change out from under us. I didn't want to have to think about that > split-state problem, so I err'd on the side of calculate-once and do the > whole operation based on that state. Maybe forwarding whether the VMA was accessed could end up cleaner. But yeah, it depends on how patch #4 will end up. > > I'll need to pull up some investigation notes, but I also remember there > being a situation where checking it underneath this caused more scanning > work - didn't want to regress anyone. This might be resolved by patch #4. > >> I mean, change_prot_numa() gets the vma and can query >> sysctl_numa_balancing_mode. Why not move that into the function and avoid the >> boolean parameter? -- Cheers, David