Re: [PATCH v8 00/10] Multi-size THP for anonymous memory

On 05/12/2023 03:37, John Hubbard wrote:

On 12/4/23 02:20, Ryan Roberts wrote:

quoted

Hi All,

A new week, a new version, a new name... This is v8 of a series to implement
multi-size THP (mTHP) for anonymous memory (previously called "small-sized THP"
and "large anonymous folios"). Matthew objected to "small huge" so hopefully
this fares better.

The objective of this is to improve performance by allocating larger chunks of
memory during anonymous page faults:

1) Since SW (the kernel) is dealing with larger chunks of memory than base
    pages, there are efficiency savings to be had; fewer page faults, batched PTE
    and RMAP manipulation, reduced lru list, etc. In short, we reduce kernel
    overhead. This should benefit all architectures.
2) Since we are now mapping physically contiguous chunks of memory, we can take
    advantage of HW TLB compression techniques. A reduction in TLB pressure
    speeds up kernel and user space. arm64 systems have 2 mechanisms to coalesce
    TLB entries; "the contiguous bit" (architectural) and HPA (uarch).

This version changes the name and tidies up some of the kernel code and test
code, based on feedback against v7 (see change log for details).

Using a couple of Armv8 systems, I've tested this patchset. I applied it
to top of tree (Linux 6.7-rc4), on top of your latest contig pte series
[1].

With those two patchsets applied, the mm selftests look OK--or at least
as OK as they normally do. I compared test runs between THP/mTHP set to
"always", vs "never", to verify that there were no new test failures.
Details: specifically, I set one particular page size (2 MB) to
"inherit", and then toggled /sys/kernel/mm/transparent_hugepage/enabled
between "always" and "never".

Excellent - I'm guessing this was for 64K base pages?

I also re-ran my usual compute/AI benchmark, and I'm still seeing the
same 10x performance improvement that I reported for the v6 patchset.

So for this patchset and for [1] as well, please feel free to add:

Tested-by: John Hubbard <jhubbard@nvidia.com>

Thanks!

[1] https://lore.kernel.org/all/20231204105440.61448-1-ryan.roberts@arm.com/ (local)


thanks,

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