Messages in this thread | | | Date | Wed, 24 Apr 2024 14:55:26 +0800 | Subject | Re: [RFC PATCH 0/5] add mTHP support for anonymous share pages | From | Baolin Wang <> |
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On 2024/4/23 18:41, 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?
As far as I know, some database related workloads make extensive use of shared anonymous page, such as PolarDB[1] in our Alibaba fleet, or MySQL likely also uses shared anonymous memory. And I still need to do some investigation to measure the performance.
[1] https://github.com/ApsaraDB/PolarDB-for-PostgreSQL
>> 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
Yes, I realized this after more testing.
> 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".
Sounds good to me. But I do not want to copy all same values from top-level '/sys/kernel/mm/transparent_hugepage/shmem_enabled': always within_size advise never deny force
For mTHP's shmem_enabled interface, we can just keep below values: always within_size advise never
Cause when checking if mTHP can be used for anon shmem, 'deny' is equal to 'never', and 'force' is equal to 'always'.
> Of course the huge= mount option would also need to take a per-size option in > this case. e.g. huge=2048kB:advise,64kB:always
IMO, I do not want to change the global 'huge=' mount option, which can control both anon shmem and tmpfs, but mTHP now is only applied for anon shmem. So let's keep it be same with the global sysfs interface: /sys/kernel/mm/transparent_hugepage/shmem_enabled.
For tmpfs large folio strategy, I plan to address it later, and we may need more discussion to determine if it should follow the file large folio strategy or not (no investigation now).
Thanks for reviewing.
>> TODO: >> - More testing and provide some performance data. >> - Need more discussion about the large folio allocation strategy for a 'regular >> file' operation created by memfd_create(), for example using ftruncate(fd) to specify >> the 'file' size, which need to follow the anonymous mTHP rule too? >> - Do not split the large folio when share memory swap out. >> - Can swap in a large folio for share memory. >> >> Baolin Wang (5): >> mm: memory: extend finish_fault() to support large folio >> mm: shmem: add an 'order' parameter for shmem_alloc_hugefolio() >> mm: shmem: add THP validation for PMD-mapped THP related statistics >> mm: shmem: add mTHP support for anonymous share pages >> mm: shmem: add anonymous share mTHP counters >> >> include/linux/huge_mm.h | 4 +- >> mm/huge_memory.c | 8 ++- >> mm/memory.c | 25 +++++++--- >> mm/shmem.c | 107 ++++++++++++++++++++++++++++++---------- >> 4 files changed, 108 insertions(+), 36 deletions(-) >>
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