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

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.

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

Best Regards
Barry