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

Ye Liu
2025-04-23T01:49:35Z

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
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
@@ -0,0 +1,120 @@
+#!/usr/bin/env drgn
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (C) 2025 Ye Liu <liuye@kylinos.cn>
+
+import argparse
+from drgn import Object
+from drgn.helpers.linux import find_task, follow_page, page_size
+from drgn.helpers.linux.mm import (
+ decode_page_flags, page_to_pfn, page_to_phys, page_to_virt, vma_find,
+ PageSlab, PageCompound, PageHead, PageTail, compound_head, compound_order, compound_nr
+)
+from drgn.helpers.linux.cgroup import cgroup_name, cgroup_path
+
+DESC = """
+This is a drgn script to show the page state.
+For more info on drgn, visit https://github.com/osandov/drgn.
+"""
+
+MEMCG_DATA_OBJEXTS = 1 << 0
+MEMCG_DATA_KMEM = 1 << 1
+__NR_MEMCG_DATA_FLAGS = 1 << 2
+
+def format_page_data(data):
+ """Format raw page data into a readable hex dump."""
+ chunks = [data[i:i+8] for i in range(0, len(data), 8)]
+ hex_chunks = ["".join(f"{b:02x}" for b in chunk[::-1]) for chunk in chunks]
+ lines = [" ".join(hex_chunks[i:i+4]) for i in range(0, len(hex_chunks), 4)]
+ return "\n".join(f"Raw: {line}" for line in lines)
+
+def get_memcg_info(page):
+ """Retrieve memory cgroup information for a page."""
+ memcg_data = page.memcg_data.value_()
+ if memcg_data & MEMCG_DATA_OBJEXTS:
+ memcg_value = 0
+ elif memcg_data & MEMCG_DATA_KMEM:
+ objcg = Object(prog, "struct obj_cgroup *", address=memcg_data & ~__NR_MEMCG_DATA_FLAGS)
+ memcg_value = objcg.memcg.value_()
+ else:
+ memcg_value = memcg_data & ~__NR_MEMCG_DATA_FLAGS
+
+ memcg = Object(prog, "struct mem_cgroup *", address=memcg_value)
+ cgrp = memcg.css.cgroup
+ return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
+
+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_(),
+ "Page PFN": hex(page_to_pfn(page).value_()),
+ "Page Physical": hex(page_to_phys(page).value_()),
+ "Page Virtual": hex(page_to_virt(page).value_()),
+ "Page Refcount": page._refcount.counter.value_(),
+ "Page Mapcount": page._mapcount.counter.value_(),
+ "Page Index": hex(page.index.value_()),
+ "Page Memcg Data": hex(page.memcg_data.value_()),
+ }
+
+ memcg_name, memcg_path = get_memcg_info(page)
+ fields["Memcg Name"] = memcg_name
+ fields["Memcg Path"] = memcg_path
+ fields["Page Mapping"] = hex(page.mapping.value_())
+ fields["Page Anon/File"] = "Anon" if page.mapping.value_() & 0x1 else "File"
+
+ vma = vma_find(mm, addr)
+ fields["Page VMA"] = hex(vma.value_())
+ fields["VMA Start"] = hex(vma.vm_start.value_())
+ fields["VMA End"] = hex(vma.vm_end.value_())
+
+ # Calculate the maximum field name length for alignment
+ max_field_len = max(len(field) for field in fields)
+
+ # Print aligned fields
+ for field, value in fields.items():
+ print(f"{field}:".ljust(max_field_len + 2) + f"{value}")
+
+ # Additional information about the page
+ if PageSlab(page):
+ print("This page belongs to the slab allocator.")
+
+ if PageCompound(page):
+ print("This page is part of a compound page.")
+ if PageHead(page):
+ print("This page is the head page of a compound page.")
+ if PageTail(page):
+ print("This page is the tail page of a compound page.")
+ print(f"{'Head Page:'.ljust(max_field_len + 2)}{hex(compound_head(page).value_())}")
+ print(f"{'Compound Order:'.ljust(max_field_len + 2)}{compound_order(page).value_()}")
+ print(f"{'Number of Pages:'.ljust(max_field_len + 2)}{compound_nr(page).value_()}")
+ else:
+ print("This page is not part of a compound page.")
+
+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)
+
+ if page:
+ show_page_state(page, vaddr, mm, args.pid, task)
+ else:
+ print(f"Address {hex(vaddr)} is not mapped.")
+
+if __name__ == "__main__":
+ main()
\ No newline at end of file
--
2.25.1