[PATCH v2] riscv: enable THP_SWAP for RV64

[Conor.Dooley at microchip.com]

On 30/08/2022 14:59, Jisheng Zhang wrote:
> On Mon, Aug 29, 2022 at 05:27:48PM +0000, Conor.Dooley at microchip.com wrote:
>> On 29/08/2022 15:10, Jisheng Zhang wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> On Sat, Aug 27, 2022 at 09:13:03PM +0000, Conor.Dooley at microchip.com wrote:
>>>> Hey Jisheng,
>>>
>>> Hi Conor,
>>>
>>>> On 27/08/2022 10:58, Jisheng Zhang wrote:
>>>>> I have a Sipeed Lichee RV dock board which only has 512MB DDR, so
>>>>> memory optimizations such as swap on zram are helpful. As is seen
>>>>> in commit d0637c505f8a ("arm64: enable THP_SWAP for arm64") and
>>>>> commit bd4c82c22c367e ("mm, THP, swap: delay splitting THP after
>>>>> swapped out"), THP_SWAP can improve the swap throughput significantly.
>>>>>
>>>>> Enable THP_SWAP for RV64, testing the micro-benchmark which is
>>>>> introduced by commit d0637c505f8a ("arm64: enable THP_SWAP for arm64")
>>>>> shows below numbers on the Lichee RV dock board:
>>>>>
>>>>> thp swp throughput w/o patch: 66908 bytes/ms (mean of 10 tests)
>>>>> thp swp throughput w/ patch: 322638 bytes/ms (mean of 10 tests)
>>>>
>>>> I know the original commit message contains this, but it's a little
>>>> odd. If the patch /enables/ THP then how would there be THP swap
>>>> prior to the patch?
>>>
>>> hmm, it's swap I'll send a v3 to correct the description.
>>>
>>>>
>>>>>
>>>>> Improved by 382%!
>>>>
>>>> I could not replicate the after numbers on my nezha, so I suspect
>>>> I am missing something in my config/setup. zswap is enabled and is
>>>
>>> swap on zram rather than zswap ;)
>>
>> I think I tried about 30 different config variations, initially not
>> using zswap and later using it.
>> My zramctl looks like so (although I did try zstd too) after running
>> the demo application from that commit:
>>
>> NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
>> /dev/zram0 lzo-rle       241M  22M  8.4M  9.1M       1 [SWAP]
>>
>> I am using the default riscv defconfig + the following:
>> CONFIG_ZRAM=y
>> CONFIG_CRYPTO_DEFLATE=y
>> CONFIG_CRYPTO_LZO=y
>> CONFIG_CRYPTO_ZSTD=y
>> CONFIG_ZRAM_MEMORY_TRACKING=y
>> CONFIG_TRANSPARENT_HUGEPAGE=y
>> CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y
>> CONFIG_THP_SWAP=y
>>
>> Am I just missing something obvious here?
> 
> similar config options here. what's your rootfs? Is your board busy
> with something? I used a minimal rootfs built from buildroot.
> can you plz show your numbers w/ and w/o the patch?

I was using fedora for the testing, downloaded directly from
koji. My before/after numbers varied, but were around 80,000
bytes/ms most of the time.

If I increased the size to 500 * 1024 * 1024 I got around 130k.

Before/after the patch, the numbers did not really change, but
things did fluctuate quite wildly - from about 50k to 90k using
the 400 size.

> 
> I also tried the simple benchmark on qemu(just for reference, since
> I have no other riscv boards except the lichee RV dock board):
> swp out w/o patch: 30066 bytes/ms (mean of 10 tests)
> swp out w/ patch: 130055 bytes/ms (mean of 10 tests)
> so improved by 332.7% 

I'll give QEMU a go so :)