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

Ye Liu
2025-04-24T03:27:27Z

在 2025/4/24 10:51, SeongJae Park 写道:
> 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
You're right — I'll update it to use prog["PAGE_SIZE"] here.
>> 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
>
> …