linux-kernel - Re: [PATCH] selftests/mm: Introduce a test program to assess swap entry allocation for thp

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Message-ID: <4bf2aecc-1c7b-420c-aa82-8613e2422407@arm.com>
Date: Fri, 21 Jun 2024 08:34:13 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Chris Li <chrisl@...nel.org>, Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, shuah@...nel.org, linux-mm@...ck.org,
 david@...hat.com, hughd@...gle.com, kaleshsingh@...gle.com,
 kasong@...cent.com, linux-kernel@...r.kernel.org, ying.huang@...el.com,
 linux-kselftest@...r.kernel.org, Barry Song <v-songbaohua@...o.com>
Subject: 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.