Re: [PATCH v4 3/3] powerpc: Kconfig: Enable THP_SWAP on Book3S64

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Barry Song <baohua@kernel.org> writes:

> On Fri, Jun 19, 2026 at 12:41 PM Ritesh Harjani (IBM)
> <ritesh.list@gmail.com> 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.
>

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


>>
>> [1]: https://lore.kernel.org/all/20170515112522.32457-2-ying.huang@intel.com/
>
> Best Regards
> Barry