Date: Wed, 26 Jun 2024 10:13:55 +1200
From: Barry Song <21cnbao@...il.com>
To: Kairui Song <ryncsn@...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 Wed, Jun 26, 2024 at 5:22 AM Kairui Song <ryncsn@...il.com> wrote:
>
> 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>.

Thanks very much, Kairui.

I was using some toolchains on both arm64 and x86, but they didn't
complain.
I agree mman.h is the correct uapi file for MADV_PAGEOUT.

   1     72  arch/alpha/include/uapi/asm/mman.h <<MADV_PAGEOUT>>
             #define MADV_PAGEOUT 21
   2     99  arch/mips/include/uapi/asm/mman.h <<MADV_PAGEOUT>>
             #define MADV_PAGEOUT 21
   3     66  arch/parisc/include/uapi/asm/mman.h <<MADV_PAGEOUT>>
             #define MADV_PAGEOUT 21
   4    107  arch/xtensa/include/uapi/asm/mman.h <<MADV_PAGEOUT>>
             #define MADV_PAGEOUT 21
   5     73  include/uapi/asm-generic/mman-common.h <<MADV_PAGEOUT>>
             #define MADV_PAGEOUT 21

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