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b=OfncYfp3EtQ5vNQxUvpMVGVjy20dPvbDUZVeNjZTTIBBMgw+tVr5rRcNDAJqCM/PX A4MFsfzdj/e6giw52AZedON5aXr2t+tm3elUaBz7JDaimwLGKWwEhopgwzT9elam+Z r2jAMWZWdkpgCQBTpYhE3WvmlOjNA7Xba3VRUl6r66KvqVary9j/kFBhvR0c5Uij0s NhcEavOdPUuFaQ7tSOYFKJ7Qfad13KoFQiB8BvoQX1yg4DWTwTwkpa9badb9d8MiLk w5W6t9g3nngB9eO+QwuatNiWEahkhk9hTZmgFxteQI2y7KwWgzD2cmE+BSKnD+w5gw RxQn38HVyRYZA== Message-ID: Date: Thu, 1 Oct 2026 12:55:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/numa_balancing: allow migrate on protnone reference with MPOL_WEIGHTED_INTERLEAVE policy To: Gregory Price Cc: Li Zhe , akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260930072617.64665-1-lizhe.67@bytedance.com> 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-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B764BC0004 X-Stat-Signature: 9sxax45ea7h7bit8fst6b4cbc1kgwbcz X-HE-Tag: 1790852120-571795 X-HE-Meta: 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 Nb4R0Pkh StHkPTPm/TPHmaqbOYGvun5ZCpvY5I+MQtJbWzxQzy7VjQzkYgboLdXalrGDDF7qfcWtdcxpQfnrN4AH9fGi05a3XGVlqdLx3z29oa109aHyR8G9dO5pvAN1oX75K/qZEsqqHNhYr1bnDPAE+kCCV/x6NHYNraXN4vroe6NCKs/xfBUPXGIf3xU5fyhnV8M0Ob+PjUS3ThVVunoreSP3MqRVDpizS0Bl+idmi+5Wb9YF9wCMyLuInlz2+qu16A5mjySJRnUWlAdr8Va7T7sGgiMi+LlLgx06DQHPBHAHsGhBoHp9RQmPdn8Gia0xUDyADJbREujAUH2/8VAjglYve8uFvmes2QLqdwxIRk8ogZRMwVECbL2hhtZmf49Qj5m2RDZQw Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/30/26 15:40, Gregory Price wrote: > On Wed, Sep 30, 2026 at 02:32:16PM +0200, David Hildenbrand (Arm) wrote: >>> >>> Right, but you're requesting this configuration. If you didn't set >>> F_NUMA_BALANCING then you get the existing semantics. >>> >>> In the existing semantics, if we're INTERLEAVE and WEIGHTED_INTERLEAVE >>> we just always say "no tiering for you". >>> >>> But as an opt-in option? I don't quite see the argument for saying >>> interleaved regions (or tasks) to be opted-out if the user asks for it - >>> that just seems like an arbitrary limitation. >> >> Just to be clear, what I am saying is: the proposed semantics are inconsistent >> (weighted when mechanism A honors them and mechanism B doesn't honor them), but >> once we set these semantics in stone like that, we cannot easily change them >> later because some user might depend on that behavior. >> >> So you'll need yet another flag to say "NUMA balancing really also honors the >> weights". And that's where it all gets ugly. >> > > I would agree with you if demotion didn't entirely ignoring mempolicy. > > On a tiered system, mempolicy *only* applies to initial (or fault-in) > placement, and otherwise is more or less entirely ignored. This is > a case where it's not ignored - which is actually inconsistent with > the rest of the tiering tools (demotion, damon). > > This is why I said this distinction may only make sense in TIERING > mode, while in NORMAL mode you likely just want to fault it back to > its original interleave location. > > Also file interleave (indexed by offset) vs task (counter-incremented) > policies are affected by these changes very differently, which I asked > for some thought on. > > As tiering develops, the less I think task-mempolicy as a whole makes > much sense (because it's at-best advisory). Fully agreed to that. I even struggle to understand how an initial placement using the weighted policy really fits into that picture. -- Cheers, David