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Static Reservation: hugetlbfs requires pre-allocating huge pages >>> at boot >>>    or runtime, taking memory away. This requires capacity planning, >>>    administrative overhead, and makes workload orchastration much >>> much more >>>    complex, especially colocating with workloads that don't use >>> hugetlbfs. >>> >> To address the obvious objection "but how could we >> possibly allocate 1GB huge pages while the workload >> is running?", I am planning to pick up the CMA balancing >> patch series (thank you, Frank) and get that in an >> upstream ready shape soon. >> >> https://lkml.org/2025/9/15/1735 > > That link doesn't work? > > Did a quick search for CMA balancing on lore, couldn't find anything, could you > provide a lore link? https://lwn.net/Articles/1038263/ > >> >> That patch set looks like another case where no >> amount of internal testing will find every single >> corner case, and we'll probably just want to >> merge it upstream, deploy it experimentally, and >> aggressively deal with anything that might pop up. > > I'm not really in favour of this kind of approach. There's plenty of things that > were considered 'temporary' upstream that became rather permanent :) > > Maybe we can't cover all corner-cases, but we need to make sure whatever we do > send upstream is maintainable, conceptually sensible and doesn't paint us into > any corners, etc. > >> >> With CMA balancing, it would be possibly to just >> have half (or even more) of system memory for >> movable allocations only, which would make it possible >> to allocate 1GB huge pages dynamically. > > Could you expand on that? I also would like to hear David’s opinion on using CMA for 1GB THP. He did not like it[1] when I posted my patch back in 2020, but it has been more than 5 years. :) The other direction I explored is to get 1GB THP from buddy allocator. That means we need to: 1. bump MAX_PAGE_ORDER to 18 or make it a runtime variable so that only 1GB THP users need to bump it, 2. handle cross memory section PFN merge in buddy allocator, 3. improve anti-fragmentation mechanism for 1GB range compaction. 1 is easier-ish[2]. I have not looked into 2 and 3 much yet. [1] https://lore.kernel.org/all/52bc2d5d-eb8a-83de-1c93-abd329132d58@redhat.com/ [2] https://lore.kernel.org/all/20210805190253.2795604-1-zi.yan@sent.com/ Best Regards, Yan, Zi