Barry Song [off-list ref] writes:

On Fri, Jun 19, 2026 at 12:41 PM Ritesh Harjani (IBM)
[off-list ref] wrote:

quoted

THP_SWAP avoids splitting of a transparent huge folio into 32 smaller
64K folios (Radix-64K pagesize / 2M PMD) or into 256 smaller 64K folios
(Hash-64K pagesize / 16M PMD), during swapout. This improves the
swapping performance since all the bookking & I/O submission happens
once per large folio. More details at [1].

PowerPC Book3S64 could not enable this before because PMD_ORDER is
selected at runtime depending upon the chosen MMU. The earlier patches
in this series turn SWAPFILE_CLUSTER into a runtime value and introduce
an ARCH_MAX_PMD_ORDER upperbound override for SWAP_NR_ORDERS. With those
changes, we can now enable THP SWAP for Book3S64.

This increases bandwidth throughput with zram backend for swapout by
40-50% with Radix and 100-130% with Hash (Tested by Sayali)

Thanks!

I am curious about the contents of the anonymous memory being tested
and the compression algorithm used by zram.

I am sure it was derived from your microbenchmark itself which you had
shared here (so repetitive pattern) with default zram compression
algorithm. Thanks for that :)

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d0637c505f

I think I got your point - I can mention that it was a microbenchmark
similar to yours and not a real world workload test. Is this what you
meant here?

-ritesh

quoted

[1]: https://lore.kernel.org/all/20170515112522.32457-2-ying.huang@intel.com/ (local)

Best Regards
Barry