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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce589a21sm383854f8f.23.2025.10.09.11.51.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Oct 2025 11:51:56 -0700 (PDT) Message-ID: Date: Thu, 9 Oct 2025 20:51:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable sysctl" To: Gregory Price , Michal Hocko Cc: linux-mm@kvack.org, corbet@lwn.net, muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, hannes@cmpxchg.org, laoar.shao@gmail.com, brauner@kernel.org, mclapinski@google.com, joel.granados@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Mel Gorman , Alexandru Moise <00moses.alexander00@gmail.com>, Mike Kravetz , David Rientjes References: <20251007214412.3832340-1-gourry@gourry.net> <402170e6-c49f-4d28-a010-eb253fc2f923@redhat.com> <271f9af4-695c-4aa5-9249-2d21ad3db76e@redhat.com> <83e33641-8c42-4341-8e6e-5c75d00f93b9@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: dtsjiz3pjwjyzn8fqfzmnyonmneth6s9 X-Rspam-User: X-Rspamd-Queue-Id: 24C7FC0012 X-HE-Tag: 1760035920-284098 X-HE-Meta: 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 coOMi3NL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 09.10.25 17:29, Gregory Price wrote: > On Thu, Oct 09, 2025 at 08:14:22AM +0200, Michal Hocko wrote: >> On Wed 08-10-25 12:31:22, Gregory Price wrote: >>>> I'm not quite clear yet on the use case, though. If all the user allocations >>>> end up fragmenting the memory, there is also not a lot of benefit to be had >>>> from that zone long term. >>>> >>> >>> The only real use case i've seen is exactly: >>> - Don't want random GFP_KERNEL to land there >>> - Might want it to be pinnable >>> >>> I think that covers what you've described above. >>> >>> But adding an entire zone felt a bit heavy handed. Allowing gigantic in >>> movable seemed less - immediately - offensive. >> >> The question is whether we need a full zone for that or we can control >> those allocation constrains on per memory block bases to override >> otherwise default. So it wouldn't be MOVABLE but rather something like >> USER zone. > > > Mild ignorance here - but I don't think the buddy allocator currently > differentiates chunks of memory based on block membership, it just eats > folios from certain zones/nodes. > > I'm scratching my head trying to think of the discrete mechanism to do > this that doesn't inject significantly more complexity into the buddy > allocator. > > Looking at the recent[1] THP support for ZONE_DEVICE, I wonder if we end > up with something more along these lines? But this aschews the other > requirement of wanting the memory to be otherwise general purpose. > > https://lore.kernel.org/linux-mm/20251001065707.920170-1-balbirs@nvidia.com/ > > ZONE_USER does feel like the most natural solution. Literally just > (ZONE_NORMAL - GFP_KERNEL). This might need a new GFP flag for certain > use cases like KVM (GFP_USER) to denote certain "This isn't technically > kernel memory, but it needs to be pinnable". That would slot right > between ZONE_NORMAL and ZONE_MOVABLE. > > Alternatively we could go the opposite way and introduce ZONE_KERNEL > below ZONE_NORMAL and disallow GFP_KERNEL from ZONE_NORMAL - then have > strict watermarks on ZONE_KERNEL to ensure the kernel is always able > to get memory. I'm afraid any new zone will be highly controversial and take a long time to get accepted, if ever :) The real question is: would we really need a system where we mix e.g., ZONE_USER with ZONE_MOVABLE? Or would it be sufficient to selectively enable (explicit opt-in) some user pages to end up on ZONE_MOVABLE? IOW, change the semantics of the zone by an admin. Like, allowing longterm pinning on ZONE_MOVABLE. Sure, it would degrade memory hotunplug (until the relevant applications are shut down) and probably some other things. Further, I am not so sure about the value of having ZONE_MOVABLE sprinkled with small unmovable allocations (same concern regarding any such zone that allows for unmovable things). Kind of against the whole concept. But I mean, if the admin decides to do that (opt in), so he is to blame. -- Cheers David / dhildenb