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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8f4bdcsm30484973f8f.54.2025.10.08.08.43.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Oct 2025 08:43:25 -0700 (PDT) Message-ID: <83e33641-8c42-4341-8e6e-5c75d00f93b9@redhat.com> Date: Wed, 8 Oct 2025 17:43:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable sysctl" To: Michal Hocko Cc: Gregory Price , 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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 8gocjx17zpp4j6zpgqkng7qfqm1ph4pq X-Rspamd-Queue-Id: D621FC000F X-Rspamd-Server: rspam09 X-HE-Tag: 1759938209-688147 X-HE-Meta: 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 3shMbPf0 qK8U1bcqyuF2drpGPv2+5mFhKEW0OUGM0CnG8qEhmoUjOIPiaKAm8Cb1sTv/cNQdgfLxHugLnmAbJJkvf/c7Phni8pxx35r98UQVOHdoLinxiqOD5X+G6qXStvQ5gI03DUM3uvnacXrtTHIOIko8bX7xbuyu5uKsPixt6gxgtW/sA5CkvfaVOSikqsAlDXAApxxfoo065FsKVuqh3M96D//LHuWiJ/fk73rhl1qcQz7S/X4Tc1ouxpSW44dQ4zO/LSc78JtzUuB17tpgdbHKqdloRsfWrhygnwldcAq8IYusWu88ler1//CPyXvY6KBH1Pp6Ouq8QJ0K1am2T9+Og9JQnj+ai6dwCGBKuDWnfw90QQtJTuVLad+1ZC3rzb2wJ74POd2JOu/j4rhcSU7apt6iMYx61DPebzgn6FG9vtm68Z6NP+aGQA2eiamMfOeJuPYI8lE4Gl2cTcPVHbUqGhqjoLqiXWwU6HLNHvDn7ZInLqfsQBX3Ch/qvHN0J/x6PikRKSHJom+BAH4jaUUziZ5/gxEAyC0n2bEWHKq/rfAtm1TAqKml7IGKmkgnjgQzzq3RexHNlAxB5VFqVzIa8ED4dqID3hFSQL98L7LC+0FvGXuhjKWx/+UHsgw== 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 08.10.25 17:23, Michal Hocko wrote: > On Wed 08-10-25 17:14:26, David Hildenbrand wrote: >> On 08.10.25 16:59, Michal Hocko wrote: >>> On Wed 08-10-25 10:58:23, David Hildenbrand wrote: >>>> On 07.10.25 23:44, Gregory Price wrote: >>> [...] >>>>> @@ -926,7 +927,8 @@ static inline gfp_t htlb_alloc_mask(struct hstate *h) >>>>> { >>>>> gfp_t gfp = __GFP_COMP | __GFP_NOWARN; >>>>> - gfp |= hugepage_movable_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER; >>>>> + gfp |= (hugepage_movable_supported(h) || hugepages_treat_as_movable) ? >>>>> + GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER; >>>> >>>> I mean, this is as ugly as it gets. >>>> >>>> Can't we just let that old approach RIP where it belongs? :) >>>> >>>> If something unmovable, it does not belong on ZONE_MOVABLE, as simple as that. >>> >>> yes, I do agree. This is just muddying the semantic of the zone. >>> >>> Maybe what we really want is to have a configurable zone rather than a >>> very specific consumer of it instead. What do I mean by that? We clearly >>> have physically (DMA, DMA32) and usability (NORMAL, MOVABLE) constrained >>> zones. So rather than having a MOVABLE zone we can have a single zone >>> $FOO_NAME zone with configurable attributes - like allocation >>> constrains (kernel, user, movable, etc). Now that we can overlap zones >>> this should allow for quite a lot flexibility. Implementation wise this >>> would require some tricks as we have 2 zone types for potentially 3 >>> different major usecases (kernel allocations, userspace reserved ranges >>> without movability and movable allocations). I haven't thought this >>> through completely and mostly throwing this as an idea (maybe won't >>> work). Does that make sense? >> >> I suggested something called PREFER_MOVABLE in the past, that would prefer >> movable allocations but nothing would stop unmovable allocations to end up >> on it. But only as a last resort or when explicitly requested (e.g., >> gigantic pages). >> >> Maybe that's similar to what you have in mind? > > Slightly different because what I was thinking about was more towards > guarantee/predictability. Last resort is quite hard to plan around. It > might be a peak memory pressure to eat up portion of a memory block and > then fragmenting it to prevent other use planned for that memroy block. > That is why I called it user allocations because those are supposed to > be configured for userspace consumation and planned for that use. So you > would get pretty much a guarantee that no kernel allocations will fall > there. What could end up on it that would not already end up on ZONE_MOVABLE? I guess long-term pinned pages, secretmem, guest_memfd, gigantic pages. Anything else? 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. -- Cheers David / dhildenb