Re: [RESEND v7 00/29] mm: PMD-level swap entries for anonymous THPs

[Andrew Morton]

On Tue, 15 Sep 2026 15:09:16 +0100 Usama Arif <usama.arif@xxxxxxxxx> wrote:

> 
> Four workers repeatedly write the working set, forcing memory to be
> swapped out and back in. The results below are the medians of five
> interleaved runs per kernel, following one warm-up run:
> 
> Metric                           Baseline median   Patched median   Change
> Aggregate benchmark throughput   584.3 MiB/s       2,408.9 MiB/s    +312.2% (4.12x)
> Elapsed time                     85.43 s           20.72 s          -75.7%
> Major faults                     1,814,699         228,466          -87.4%
> Swap I/O rate                    1.02 GiB/s        4.10 GiB/s       +303.9%
> 
> The results look good as this is a swap-intensive workload.
> It primarily demonstrates the reduction in swap-fault and page-table
> overhead from preserving PMD mappings.
> 
> For long-running workloads, where I believe the series will shine, I expect
> benefits from fewer TLB misses, less khugepaged work as well as less kernel churn
> due to larger folios, although there aren't a lot of benchmarks to test that.
> PMD swap entries also move us closer to eliminating page-table deposits for
> anonymous THPs, which would provide memory savings.
> 

Thanks.  Wow.

This doesn't look totally real-world but it's close enough to indicate
that real people doing real things will see nice benefits from this
change.  As expected - leaving post-swapin thp reassembly to khugepaged
was so lame.

Please add the above info to the [0/N] and maintain it.

(I'm itching to get this moving ahead, but we do need eyes on those
core bits).