On 24/04/2024 10:55, Baolin Wang wrote: > > > On 2024/4/24 16:26, Ryan Roberts wrote: >> On 24/04/2024 07:55, Baolin Wang wrote: >>> >>> >>> 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 >> >> Thanks for the pointer! >> >>> >>>>> 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'. >> >> I'll admit it wasn't completely clear to me after reading the docs, but my rough >> understanding is: >> >> - /sys/kernel/mm/transparent_hugepage/shmem_enabled controls >> mmap(SHARED|ANON) allocations (mostly; see rule 3) >> - huge=... controls tmpfs allocations >> - deny and force in shmem_enabled are equivalent to never and always for >> mmap(SHARED|ANON) but additionally override all tmpfs mounts so they act as >> if they were mounted with huge=never or huge=always >> >> Is that correct? If so, then I think it still makes sense to support per-size > > Correct. > >> deny/force. Certainly if a per-size control is set to "inherit" and the >> top-level control is set to deny or force, you would need that to mean something. > > IMHO, the '/mm/transparent_hugepage/hugepage-XXkb/shmem_enabled' interface > should only control the anonymous shmem. And 'huge=' controls tmpfs allocation, > so we should not use anonymous control to override tmpfs control, which seems a > little mess? I agree it would be cleaner to only handle mmap(SHARED|ANON) here, and leave the tmpfs stuff for another time. But my point is that /mm/transparent_hugepage/shmem_enabled already interferes with tmpfs if the value is deny or force. So if you have: echo deny > /mm/transparent_hugepage/shmem_enabled echo inherit > /mm/transparent_hugepage/hugepage-64kB/shmem_enabled What does that mean? > >>>> 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 >> >> How does huge= control anon shmem? I thought it was only for mounted >> filesystems; so tmpfs? Perhaps my mental model for how this works is broken... > > Sorry for noise, you are right. So this is still the reason I don't want to > change the semantics of 'huge=', which is used to control tmpfs. > >>> 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). >> >> OK. But until you get to tmpfs, you'll need an interim definition for what it >> means if a per-size control is set to "inherit" and the top-level control is set >> to deny/force. >> >>> >>> Thanks for reviewing. >> >> No problem! Thanks for doing the work! >> >>> >>>>> 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(-) >>>>>
