Re: [PATCH v6 0/9] variable-order, large folios for anonymous memory

[Matthew Wilcox]

On Sun, Nov 12, 2023 at 10:57:47PM -0500, John Hubbard wrote:
> I've done some initial performance testing of this patchset on an arm64
> SBSA server. When these patches are combined with the arm64 arch contpte
> patches in Ryan's git tree (he has conveniently combined everything
> here: [1]), we are seeing a remarkable, consistent speedup of 10.5x on
> some memory-intensive workloads. Many test runs, conducted independently
> by different engineers and on different machines, have convinced me and
> my colleagues that this is an accurate result.
> 
> In order to achieve that result, we used the git tree in [1] with
> following settings:
> 
>     echo always >/sys/kernel/mm/transparent_hugepage/enabled
>     echo recommend >/sys/kernel/mm/transparent_hugepage/anon_orders
> 
> This was on a aarch64 machine configure to use a 64KB base page size.
> That configuration means that the PMD size is 512MB, which is of course
> too large for practical use as a pure PMD-THP. However, with with these
> small-size (less than PMD-sized) THPs, we get the improvements in TLB
> coverage, while still getting pages that are small enough to be
> effectively usable.

That is quite remarkable!

My hope is to abolish the 64kB page size configuration.  ie instead of
using the mixture of page sizes that you currently are -- 64k and
1M (right?  Order-0, and order-4), that 4k, 64k and 2MB (order-0,
order-4 and order-9) will provide better performance.

Have you run any experiements with a 4kB page size?