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

SeongJae Park
2025-04-24T02:51:30Z

On Thu, 24 Apr 2025 09:55:22 +0800 Ye Liu <ye.liu@linux.dev> wrote:

>
> 在 2025/4/24 06:00, SeongJae Park 写道:
> > 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 size refers to the base page size, which equals PAGESIZE.

Shouldn't 'prog["PAGE_SIZE"]' is used for what you are saying? This tool is
using drgn.helpers.linux.page_size()[1] to print this, though?

+def show_page_state(page, addr, mm, pid, task):
+ """Display detailed information about a page."""
+ print(f'PID: {pid} Comm: {task.comm.string_().decode()} mm: {hex(mm)}')
+ print(format_page_data(prog.read(page.value_(), 64)))
+ fields = {
+ "User Virtual Address": hex(addr),
+ "Page Address": hex(page.value_()),
+ "Page Flags": decode_page_flags(page),
+ "Page Size": page_size(page).value_(),

[1] https://drgn.readthedocs.io/en/stable/helpers.html#drgn.helpers.linux.mm.page_size

> Folio size can be calculated using the Compound Order, but of course,
> it can also be shown directly as a result.
>
> >> 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);
>
> To avoid address truncation, you can use the %p format specifier
> instead of %x or %lx when printing a pointer (memory address).

Ah, you're correct, thank you. After fixing my test, the error I reported
before is disappeared. But I think the follow_page() error handling would
better to be updated to catch the exception and provide a better error message?

Also, I'm getting below new error:

$ sudo ./tools/mm/show_page_info.py 47657 0x7fffaf925b6c
PID: 47657 Comm: a.out mm: 0xffff959c8a022100
Raw: 0017ffffc0020828 ffffea6b0c201408 ffffea6b0fc65648 ffff959d32bec9c1
Raw: 00000007fffffffc 0000000000000000 0000000100000000 ffff959cba058000
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 115, in main
show_page_state(page, vaddr, mm, args.pid, task)
File "./tools/mm/show_page_info.py", line 63, in show_page_state
memcg_name, memcg_path = get_memcg_info(page)
^^^^^^^^^^^^^^^^^^^^
File "./tools/mm/show_page_info.py", line 43, in get_memcg_info
return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/dist-packages/drgn-0.0.30+82.ge2b60e4b-py3.11-linux-x86_64.egg/drgn/helpers/linux/cgroup.py", line 71, in cgroup_name
return kernfs_name(cgrp.kn)
^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/dist-packages/drgn-0.0.30+82.ge2b60e4b-py3.11-linux-x86_64.egg/drgn/helpers/linux/kernfs.py", line 32, in kernfs_name
return kn.name.string_() if kn.parent else b"/"
^^^^^^^^^
AttributeError: 'struct kernfs_node' has no member 'parent'. Did you mean: '__parent'?

Seems not entirely this script's fault but due to the recent 'struct
kernfs_node' change or my old version of drgn? But anyway, I think it is
better to provide a better error message to users. I'm also curious if you
have a plan for finding and fixing or avoiding this kind of future breakages.

Thanks,
SJ …