Messages in this thread | | | Date | Tue, 23 Apr 2024 13:05:07 +0200 | Subject | Re: [RFC PATCH 0/5] add mTHP support for anonymous share pages | From | David Hildenbrand <> |
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On 23.04.24 12:41, Ryan Roberts wrote: > On 22/04/2024 08:02, Baolin Wang wrote: >> Anonymous pages have already been supported for multi-size (mTHP) allocation >> through commit 19eaf44954df, that can allow THP to be configured through the >> sysfs interface located at '/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled'. >> >> However, the anonymous shared pages will ignore the anonymous mTHP rule >> configured through the sysfs interface, and can only use the PMD-mapped >> THP, that is not reasonable. Many implement anonymous page sharing through >> mmap(MAP_SHARED | MAP_ANONYMOUS), especially in database usage scenarios, >> therefore, users expect to apply an unified mTHP strategy for anonymous pages, >> also including the anonymous shared pages, in order to enjoy the benefits of >> mTHP. For example, lower latency than PMD-mapped THP, smaller memory bloat >> than PMD-mapped THP, contiguous PTEs on ARM architecture to reduce TLB miss etc. > > This sounds like a very useful addition! > > Out of interest, can you point me at any workloads (and off-the-shelf benchmarks > for those workloads) that predominantly use shared anon memory? > >> >> The primary strategy is that, the use of huge pages for anonymous shared pages >> still follows the global control determined by the mount option "huge=" parameter >> or the sysfs interface at '/sys/kernel/mm/transparent_hugepage/shmem_enabled'. >> The utilization of mTHP is allowed only when the global 'huge' switch is enabled. >> Subsequently, the mTHP sysfs interface (/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled) >> is checked to determine the mTHP size that can be used for large folio allocation >> for these anonymous shared pages. > > I'm not sure about this proposed control mechanism; won't it break > compatibility? I could be wrong, but I don't think shmem's use of THP used to > depend upon the value of /sys/kernel/mm/transparent_hugepage/enabled? So it > doesn't make sense to me that we now depend upon the > /sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled values (which by > default disables all sizes except 2M, which is set to "inherit" from > /sys/kernel/mm/transparent_hugepage/enabled). > > The other problem is that shmem_enabled has a different set of options > (always/never/within_size/advise/deny/force) to enabled (always/madvise/never) > > Perhaps it would be cleaner to do the same trick we did for enabled; Introduce > /mm/transparent_hugepage/hugepage-XXkb/shmem_enabled, which can have all the > same values as the top-level /sys/kernel/mm/transparent_hugepage/shmem_enabled, > plus the additional "inherit" option. By default all sizes will be set to > "never" except 2M, which is set to "inherit".
Matches what I had in mind.
-- Cheers,
David / dhildenb
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