linux-kernel - Re: [PATCH v2 1/1] tools/mm: Introduce a tool to assess swap entry allocation for thp

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Date: Wed, 26 Jun 2024 01:22:17 +0800
From: Kairui Song <ryncsn@...il.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, chrisl@...nel.org, linux-mm@...ck.org, 
	ryan.roberts@....com, david@...hat.com, hughd@...gle.com, 
	kaleshsingh@...gle.com, linux-kernel@...r.kernel.org, v-songbaohua@...o.com, 
	ying.huang@...el.com
Subject: Re: [PATCH v2 1/1] tools/mm: Introduce a tool to assess swap entry
 allocation for thp_swapout

On Sat, Jun 22, 2024 at 3:13 PM Barry Song <21cnbao@...il.com> wrote:
>
> From: Barry Song <v-songbaohua@...o.com>
>
> Both Ryan and Chris have been utilizing the small test program to aid
> in debugging and identifying issues with swap entry allocation. While
> a real or intricate workload might be more suitable for assessing the
> correctness and effectiveness of the swap allocation policy, a small
> test program presents a simpler means of understanding the problem and
> initially verifying the improvements being made.
>
> Let's endeavor to integrate it into tools/mm. Although it presently
> only accommodates 64KB and 4KB, I'm optimistic that we can expand
> its capabilities to support multiple sizes and simulate more
> complex systems in the future as required.
>
> Basically, we have
> 1. Use MADV_PAGEPUT for rapid swap-out, putting the swap allocation code
> under high exercise in a short time.
> 2. Use MADV_DONTNEED to simulate the behavior of libc and Java heap in
> freeing memory, as well as for munmap, app exits, or OOM killer scenarios.
> This ensures new mTHP is always generated, released or swapped out, similar
> to the behavior on a PC or Android phone where many applications are
> frequently started and terminated.
> 3. Swap in with or without the "-a" option to observe how fragments
> due to swap-in and the incoming swap-in of large folios will impact
> swap-out fallback.
>
> Due to 2, we ensure a certain proportion of mTHP. Similarly, because
> of 3, we maintain a certain proportion of small folios, as we don't
> support large folios swap-in, meaning any swap-in will immediately
> result in small folios. Therefore, with both 2 and 3, we automatically
> achieve a system containing both mTHP and small folios. Additionally,
> 1 provides the ability to continuously swap them out.
>
> We can also use "-s" to add a dedicated small folios memory area.
>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> ---
>  tools/mm/Makefile                  |   2 +-
>  tools/mm/thp_swap_allocator_test.c | 233 +++++++++++++++++++++++++++++
>  2 files changed, 234 insertions(+), 1 deletion(-)
>  create mode 100644 tools/mm/thp_swap_allocator_test.c
>
> diff --git a/tools/mm/Makefile b/tools/mm/Makefile
> index 7bb03606b9ea..15791c1c5b28 100644
> --- a/tools/mm/Makefile
> +++ b/tools/mm/Makefile
> @@ -3,7 +3,7 @@
>  #
>  include ../scripts/Makefile.include
>
> -BUILD_TARGETS=page-types slabinfo page_owner_sort
> +BUILD_TARGETS=page-types slabinfo page_owner_sort thp_swap_allocator_test
>  INSTALL_TARGETS = $(BUILD_TARGETS) thpmaps
>
>  LIB_DIR = ../lib/api
> diff --git a/tools/mm/thp_swap_allocator_test.c b/tools/mm/thp_swap_allocator_test.c
> new file mode 100644
> index 000000000000..a363bdde55f0
> --- /dev/null
> +++ b/tools/mm/thp_swap_allocator_test.c
> @@ -0,0 +1,233 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * 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 swapin/out 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
> + * The expected result should be 0% anon swpout fallback ratio w/ or
> + * w/o "-s".
> + *
> + * Author(s): Barry Song <v-songbaohua@...o.com>
> + */
> +
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <sys/mman.h>

Hi Barry,

Found a small issue while testing your tool.. for better
compatibility, I think you missed <linux/mman.h>, I'm getting
following error without it (with glibc-headers-2.28-236 on el8
system):

thp_swap_allocator_test.c:161:30: error: ‘MADV_PAGEOUT’ undeclared
(first use in this function); did you mean ‘MADV_RANDOM’?
  madvise(mem1, MEMSIZE_MTHP, MADV_PAGEOUT);
                              ^~~~~~~~~~~~

Other in-tree test tools using this flag also includes <linux/mman.h>.