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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8a6c3esm29244385f8f.1.2025.10.08.01.58.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Oct 2025 01:58:26 -0700 (PDT) Message-ID: <402170e6-c49f-4d28-a010-eb253fc2f923@redhat.com> Date: Wed, 8 Oct 2025 10:58:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable sysctl" To: Gregory Price , linux-mm@kvack.org Cc: 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 , Michal Hocko , Alexandru Moise <00moses.alexander00@gmail.com>, Mike Kravetz , David Rientjes References: <20251007214412.3832340-1-gourry@gourry.net> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20251007214412.3832340-1-gourry@gourry.net> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: JFuguDMVhEHSfrS3dXLJp6kWHvFfCV-bZlNrqRpEV2Y_1759913907 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 89DA6140006 X-Rspamd-Server: rspam03 X-Stat-Signature: sngdpim7n8ycosx87yfq3asy1x8oysy1 X-HE-Tag: 1759913910-846264 X-HE-Meta: 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 CgYe+U4N yObwKEPJT0BF6+fyNQUrZDJFTv768clxpbiwAi2qgxYNZtbg6xZdYiCJ8rhHMYXyF+PsuPMbZFtT3dub0WznyMbxqs8L8SEXxLuwzhZkPVNd7uV9FarW4xj3zIeQQCUPizTC6qnuCS9OgXNgIo2Vwa0tIilosyK9qXhI3cR/DEZFz/wlZjV0Gmc+2sqKjlMrrhsjEjbeetaehlyIV7coV2F0+ZhoJoHcLL39TSUaGqv92IBj9PtOamSDITbGs8tx4p22DLIsdZSKVSMG2lXz/IJ2rAd46hC/Ef6kw2jeklAlguVnS7MhXuG8/KLi7X8BnO3uRODlY3QccWCKUItOE/4P7LoSjWwFFfhVQo+cCU2jTdThba1Bg9bNeMzeW5CkGv68E6vNlREaiJ2WX08SQpbOi6TXv6+nEDvPM5GZu8UvV94tagw2oIj+vfux0fm++2qS7TUQmMpV4eEAS1a8MiXogvUc8RRc26G9DEHeCWPfYI+Qq6wcLlaf9gQ0VG8IJdy2UH+fzaqnOscvc66sjsxYI1OIzWn0lRB3X3SE7pg9PtRRd6XPXG6A7hOJ104f3yF0e4ECV+mkDaka3G7QOBkwDnUDtDeL9W+E1zFlAXu8gVXI8tBlLhVcvMZwt/voy+9KrLqR5HNMkvAhgxWAy2UcYnk25Ro45hggj9PUZgVOjyKW0/5s+c6yqzoEUkUnGtTJAjFR/0ZroH5c8T/Y+u0NqpaBqRwlWD0xJqbYfnMYEr+9K1ahD6AiPIdyllQZ/8Z8T 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 07.10.25 23:44, Gregory Price wrote: > This reverts commit d6cb41cc44c63492702281b1d329955ca767d399. > > This sysctl provides some flexibility between multiple requirements which > are difficult to square without adding significantly more complexity. > > 1) onlining memory in ZONE_MOVABLE to maintain hotplug compatibility > 2) onlining memory in ZONE_MOVABLE to prevent GFP_KERNEL usage > 3) passing NUMA structure through to a virtual machine (node0=vnode0, > node1=vnode1) so a guest can make good placement decisions. > 4) utilizing 1GB hugepages for VM host memory to reduce TLB pressure > 5) Managing device memory after init-time to avoid incidental usage > at boot (due to being placed in ZONE_NORMAL), or to provide users > configuration flexibility. > > When device-hotplugged memory does not require hot-unplug assurances, > there is no reason to avoid allowing otherwise non-migratable hugepages > in this zone. This allows for allocation of 1GB gigantic pages for VMs > with existing mechanisms. > > Boot-time CMA is not possible for driver-managed hotplug memory, as CMA > requires the memory to be registered as SystemRAM at boot time. > > Updated the code to land in appropriate locations since it all moved. > Updated the documentation to add more context when this is useful. > > Cc: David Hildenbrand > Cc: Mel Gorman > Cc: Michal Hocko > Cc: Alexandru Moise <00moses.alexander00@gmail.com> > Cc: Mike Kravetz > Suggested-by: David Rientjes > Signed-off-by: Gregory Price > Link: https://lore.kernel.org/all/20180201193132.Hk7vI_xaU%25akpm@linux-foundation.org/ > --- > Documentation/admin-guide/sysctl/vm.rst | 31 +++++++++++++++++++++++++ > include/linux/hugetlb.h | 4 +++- > mm/hugetlb.c | 9 +++++++ > 3 files changed, 43 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst > index 4d71211fdad8..c9f26cd447d7 100644 > --- a/Documentation/admin-guide/sysctl/vm.rst > +++ b/Documentation/admin-guide/sysctl/vm.rst > @@ -40,6 +40,7 @@ Currently, these files are in /proc/sys/vm: > - enable_soft_offline > - extfrag_threshold > - highmem_is_dirtyable > +- hugepages_treat_as_movable > - hugetlb_shm_group > - laptop_mode > - legacy_va_layout > @@ -356,6 +357,36 @@ only use the low memory and they can fill it up with dirty data without > any throttling. > > > +hugepages_treat_as_movable > +========================== > + > +This parameter controls whether otherwise immovable hugepages (e.g. 1GB > +gigantic pages) may be allocated from from ZONE_MOVABLE. If set to non-zero, > +gigantic hugepages can be allocated from ZONE_MOVABLE. ZONE_MOVABLE memory > +may be created via the kernel boot parameter `kernelcore` or via memory > +hotplug as discussed in Documentation/admin-guide/mm/memory-hotplug.rst. > + > +Support may depend on specific architecture and/or the hugepage size. If > +a hugepage supports migration, allocation from ZONE_MOVABLE is always > +enabled (for example 2MB on x86) for the hugepage regardless of the value > +of this parameter. IOW, this parameter affects only non-migratable hugepages. > + > +Assuming that hugepages are not migratable in your system, one usecase of > +this parameter is that users can make hugepage pool more extensible by > +enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE > +page reclaim/migration/compaction work more and you can get contiguous > +memory more likely. Note that using ZONE_MOVABLE for non-migratable > +hugepages can do harm to other features like memory hotremove (because > +memory hotremove expects that memory blocks on ZONE_MOVABLE are always > +removable,) so it's a trade-off responsible for the users. > + > +One common use-case of this feature is allocate 1GB gigantic pages for > +virtual machines from otherwise not-hotplugged memory which has been > +isolated from kernel allocations by being onlined into ZONE_MOVABLE. > +These pages tend to be allocated and released more explicitly, and so > +hotplug can still be achieved with appropriate orchestration. > + > + > hugetlb_shm_group > ================= > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 526d27e88b3b..bbaa1b4908b6 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -172,6 +172,7 @@ bool hugetlbfs_pagecache_present(struct hstate *h, > > struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio); > > +extern int hugepages_treat_as_movable; > extern int sysctl_hugetlb_shm_group; > extern struct list_head huge_boot_pages[MAX_NUMNODES]; > > @@ -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. Something I could sympathize is is treaing gigantic pages that are actually migratable as movable. Like diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 526d27e88b3b2..78da85b1308dd 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -896,37 +896,12 @@ static inline bool hugepage_migration_supported(struct hstate *h) return arch_hugetlb_migration_supported(h); } -/* - * Movability check is different as compared to migration check. - * It determines whether or not a huge page should be placed on - * movable zone or not. Movability of any huge page should be - * required only if huge page size is supported for migration. - * There won't be any reason for the huge page to be movable if - * it is not migratable to start with. Also the size of the huge - * page should be large enough to be placed under a movable zone - * and still feasible enough to be migratable. Just the presence - * in movable zone does not make the migration feasible. - * - * So even though large huge page sizes like the gigantic ones - * are migratable they should not be movable because its not - * feasible to migrate them from movable zone. - */ -static inline bool hugepage_movable_supported(struct hstate *h) -{ - if (!hugepage_migration_supported(h)) - return false; - - if (hstate_is_gigantic(h)) - return false; - return true; -} - /* Movability of hugepages depends on migration support. */ 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_migration_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER; return gfp; } Assume you want to offline part of the ZONE_MOVABLE there might still be sufficient space to possibly allocate a 1 GiB area elsewhere and actually move the gigantic page. IIRC, we do the same for memory offlining already. Now, maybe we want to make the configurable. But then, I would much rather tweak the hstate_is_gigantic() check in hugepage_movable_supported(). And the parameter would need a much better name than some "treat as movable". -- Cheers David / dhildenb