Re: [PATCH v3] tools/mm: Add script to display page state for a given PID and VADDR

SeongJae Park
2025-04-23T22:00:21Z

On Wed, 23 Apr 2025 09:48:50 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
>
> Introduces a new drgn script, `show_page_info.py`, which allows users
> to analyze the state of a page given a process ID (PID) and a virtual
> address (VADDR). This can help kernel developers or debuggers easily
> inspect page-related information in a live kernel or vmcore.
>
> The script extracts information such as the page flags, mapping, and
> other metadata relevant to diagnosing memory issues.
>
> Output example:
> sudo ./show_page_info.py 1 0x7f43df5acf00
> PID: 1 Comm: systemd mm: 0xffff8881273bbc40
> Raw: 0017ffffc000416c ffffea00043a4508 ffffea0004381e08 ffff88810f086a70
> Raw: 0000000000000000 ffff888120c9b0c0 0000002500000007 ffff88812642c000
> User Virtual Address: 0x7f43df5acf00
> Page Address: 0xffffea00049a0b00
> Page Flags: PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
> PG_private|PG_reported
> Page Size: 16384

Should this be called folio size? Or, could this simply removed since Compound
Order is given below?

> Page PFN: 0x12682c
> Page Physical: 0x12682c000
> Page Virtual: 0xffff88812682c000
> Page Refcount: 37
> Page Mapcount: 7
> Page Index: 0x0
> Page Memcg Data: 0xffff88812642c000
> Memcg Name: init.scope
> Memcg Path: /sys/fs/cgroup/memory/init.scope
> Page Mapping: 0xffff88810f086a70
> Page Anon/File: File
> Page VMA: 0xffff88810e4af3b8
> VMA Start: 0x7f43df5ac000
> VMA End: 0x7f43df5b0000
> This page is part of a compound page.
> This page is the head page of a compound page.
> Head Page: 0xffffea00049a0b00
> Compound Order: 2
> Number of Pages: 4
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
>
> Changes in v3:
> - Adjust display style.
> - Link to v2:https://lore.kernel.org/all/20250421080748.114750-1-ye.liu@linux.dev/
>
> Changes in v2:
> - Move the show_page_info.py file to tools/mm.
> - Link to v1: https://lore.kernel.org/all/20250415075024.248232-1-ye.liu@linux.dev/
> ---
> MAINTAINERS | 5 ++
> tools/mm/show_page_info.py | 120 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 125 insertions(+)
> create mode 100755 tools/mm/show_page_info.py
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 17ed0b5ffdd2..85686a30dc72 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -18351,6 +18351,11 @@ F: Documentation/mm/page_table_check.rst
> F: include/linux/page_table_check.h
> F: mm/page_table_check.c
>
> +PAGE STATE DEBUG SCRIPT
> +M: Ye Liu <liuye@kylinos.cn>
> +S: Maintained
> +F: tools/mm/show_page_info.py
> +
> PANASONIC LAPTOP ACPI EXTRAS DRIVER
> M: Kenneth Chan <kenneth.t.chan@gmail.com>
> L: platform-driver-x86@vger.kernel.org
> diff --git a/tools/mm/show_page_info.py b/tools/mm/show_page_info.py
> new file mode 100755
> index 000000000000..8622c5499dfe
> --- /dev/null
> +++ b/tools/mm/show_page_info.py
[...]
> +def main():
> + """Main function to parse arguments and display page state."""
> + parser = argparse.ArgumentParser(description=DESC, formatter_class=argparse.RawTextHelpFormatter)
> + parser.add_argument('pid', metavar='PID', type=int, help='Target process ID (PID)')
> + parser.add_argument('vaddr', metavar='VADDR', type=str, help='Target virtual address in hexadecimal format (e.g., 0x7fff1234abcd)')
> + args = parser.parse_args()
> +
> + try:
> + vaddr = int(args.vaddr, 16)
> + except ValueError:
> + print(f"Error: Invalid virtual address format: {args.vaddr}")
> + return
> +
> + task = find_task(args.pid)
> + mm = task.mm
> + page = follow_page(mm, vaddr)

I tried this script on my test machine and got the below error:

$ cat ./a.c
#include <stdio.h>

int main(void)
{
int foo;
printf("hello\n");
printf("%x\n", &foo);
scanf("%d\n", &foo);
return 0;
}
$ gcc ./a.c
$ ./a.out &
[2] 45666
hello
f7eb7c0c

$ sudo ./tools/mm/show_page_info.py 45666 0xf7eb7c0c
Traceback (most recent call last):
File "/usr/local/bin/drgn", line 33, in <module>
sys.exit(load_entry_point('drgn==0.0.30+82.ge2b60e4b', 'console_scripts', 'drgn')())
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/dist-packages/drgn-0.0.30+82.ge2b60e4b-py3.11-linux-x86_64.egg/drgn/cli.py", line 461, in _main
runpy.run_path(script, init_globals={"prog": prog}, run_name="__main__")
File "<frozen runpy>", line 291, in run_path
File "<frozen runpy>", line 98, in _run_module_code
File "<frozen runpy>", line 88, in _run_code
File "./tools/mm/show_page_info.py", line 120, in <module>
main()
File "./tools/mm/show_page_info.py", line 112, in main
page = follow_page(mm, vaddr)
^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/dist-packages/drgn-0.0.30+82.ge2b60e4b-py3.11-linux-x86_64.egg/drgn/helpers/linux/mm.py", line 1068, in follow_page
return phys_to_page(follow_phys(mm, addr))
^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/dist-packages/drgn-0.0.30+82.ge2b60e4b-py3.11-linux-x86_64.egg/drgn/helpers/linux/mm.py", line 1109, in follow_phys
return Object(prog, "phys_addr_t", _linux_helper_follow_phys(prog, mm.pgd, addr))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_drgn.FaultError: address is not mapped: 0xf7eb7c0c

Am I doing something wrong?

Thanks,
SJ …