Re: [PATCH] selftests/mm: Introduce a test program to assess swap entry allocation for thp_swapout

On 21/06/2024 00:34, Chris Li wrote:

...

• • thp_swap_allocator_test
• • The purpose of this test program is helping check if THP swpout
• • can correctly get swap slots to swap out as a whole instead of
• • being split. It randomly releases swap entries through madvise
• • DONTNEED and do swapout on two memory areas: a memory area for
• • 64KB THP and the other area for small folios. The second memory
• • can be enabled by "-s".
• • Before running the program, we need to setup a zRAM or similar
• • swap device by:
• • echo lzo > /sys/block/zram0/comp_algorithm
• • echo 64M > /sys/block/zram0/disksize
• • echo never > /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
• • echo always > /sys/kernel/mm/transparent_hugepage/hugepages-64kB/enabled
• • mkswap /dev/zram0
• • swapon /dev/zram0

This setup needs to go into run_vmtest.sh as well.

Also tear it down after the test.

Additionally, if keeping this as a selftest, you'll want to add

CONFIG_ZRAM=y

to tools/testing/selftests/mm/config so that automated systems ensure zram is available in the kernel under test.

And you will need to ensure that the zram device has a higher priority than any other already configured swap devices. Otherwise there will not even be an attempt to use it for mTHP. The easy way is to do "swapoff -a" as the first step but that makes cleanup tricky.