[PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[Ye Liu]

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 0x7fc988181000
PID: 1 Comm: systemd mm: 0xffff8d22c4089700
RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
Page Address:    0xfffff93905664e00
Page Flags:      PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
                 PG_private|PG_reported|PG_has_hwpoisoned
Page Size:       4096
Page PFN:        0x159938
Page Physical:   0x159938000
Page Virtual:    0xffff8d2319938000
Page Refcount:   37
Page Mapcount:   7
Page Index:      0x0
Page Memcg Data: 0xffff8d23203ff500
Memcg Name:      init.scope
Memcg Path:      /sys/fs/cgroup/memory/init.scope
Page Mapping:    0xffff8d23062a12a8
Page Anon/File:  File
Page VMA:        0xffff8d22e06e0e40
VMA Start:       0x7fc988181000
VMA End:         0x7fc988185000
This page is part of a compound page.
This page is the head page of a compound page.
Head Page:       0xfffff93905664e00
Compound Order:  2
Number of Pages: 4

Signed-off-by: Ye Liu <liuye@kylinos.cn>

Changes in v5:
- Use platform-aware word-size reads instead of raw byte access.
- Replace Object() with drgn.cast() for type safety.
- Better handle memcg flags and error cases.
- Exit on fatal errors with sys.exit().
- Remove 'User Virtual Address'.
- Link to v4:https://lore.kernel.org/all/20250528091543.355386-1-ye.liu@linux.dev/

Changes in v4:
- Add error and exception handling.
- Adjust the way to obtain PAGE_SIZE.
- Fix the acquisition of memcg.
- Link to v3:https://lore.kernel.org/all/20250423014850.344501-1-ye.liu@linux.dev/

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 | 169 +++++++++++++++++++++++++++++++++++++
 2 files changed, 174 insertions(+)
 create mode 100644 tools/mm/show_page_info.py

diff --git a/MAINTAINERS b/MAINTAINERS
index 0cb9e55021cb..3cbd46bf1eab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18726,6 +18726,11 @@ 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 100644
index 000000000000..c46d8ea283d7
--- /dev/null
+++ b/tools/mm/show_page_info.py
@@ -0,0 +1,169 @@
+#!/usr/bin/env drgn
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (C) 2025 Ye Liu <liuye@kylinos.cn>
+
+import argparse
+import sys
+from drgn import Object, FaultError, PlatformFlags, cast
+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.
+"""
+
+def format_page_data(page):
+    """
+    Format raw page data into a readable hex dump with "RAW:" prefix.
+
+    :param page: drgn.Object instance representing the page.
+    :return: Formatted string of memory contents.
+    """
+    try:
+        address = page.value_()
+        size = prog.type("struct page").size
+
+        if prog.platform.flags & PlatformFlags.IS_64_BIT:
+            word_size = 8
+        else:
+            word_size = 4
+        num_words = size // word_size
+
+        values = []
+        for i in range(num_words):
+            word_address = address + i * word_size
+            word = prog.read_word(word_address)
+            values.append(f"{word:0{word_size * 2}x}")
+
+        lines = [f"RAW: {' '.join(values[i:i + 4])}" for i in range(0, len(values), 4)]
+
+        return "\n".join(lines)
+
+    except FaultError as e:
+        return f"Error reading memory: {e}"
+    except Exception as e:
+        return f"Unexpected error: {e}"
+
+def get_memcg_info(page):
+    """Retrieve memory cgroup information for a page."""
+    try:
+        MEMCG_DATA_OBJEXTS = prog.constant("MEMCG_DATA_OBJEXTS").value_()
+        MEMCG_DATA_KMEM = prog.constant("MEMCG_DATA_KMEM").value_()
+        mask = prog.constant('__NR_MEMCG_DATA_FLAGS').value_() - 1
+        memcg_data = page.memcg_data.read_()
+        if memcg_data & MEMCG_DATA_OBJEXTS:
+            slabobj_ext = cast("struct slabobj_ext *", memcg_data & ~mask)
+            memcg = slabobj_ext.objcg.memcg.value_()
+        elif memcg_data & MEMCG_DATA_KMEM:
+            objcg = cast("struct obj_cgroup *", memcg_data & ~mask)
+            memcg = objcg.memcg.value_()
+        else:
+            memcg = cast("struct mem_cgroup *", memcg_data & ~mask)
+
+        if memcg.value_() == 0:
+            return "none", "/sys/fs/cgroup/memory/"
+        cgrp = memcg.css.cgroup
+        return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
+    except FaultError as e:
+        return "unknown", f"Error retrieving memcg info: {e}"
+    except Exception as e:
+        return "unknown", f"Unexpected error: {e}"
+
+def show_page_state(page, addr, mm, pid, task):
+    """Display detailed information about a page."""
+    try:
+        print(f'PID: {pid} Comm: {task.comm.string_().decode()} mm: {hex(mm)}')
+        try:
+            print(format_page_data(page))
+        except FaultError as e:
+            print(f"Error reading page data: {e}")
+        fields = {
+            "Page Address": hex(page.value_()),
+            "Page Flags": decode_page_flags(page),
+            "Page Size": prog["PAGE_SIZE"].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.__folio_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"
+
+        try:
+            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_())
+        except FaultError as e:
+            fields["Page VMA"] = "Unavailable"
+            fields["VMA Start"] = "Unavailable"
+            fields["VMA End"] = "Unavailable"
+            print(f"Error retrieving VMA information: {e}")
+
+        # 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.")
+    except FaultError as e:
+        print(f"Error accessing page state: {e}")
+    except Exception as e:
+        print(f"Unexpected error: {e}")
+
+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:
+        sys.exit(f"Error: Invalid virtual address format: {args.vaddr}")
+
+    try:
+        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:
+            sys.exit(f"Address {hex(vaddr)} is not mapped.")
+    except FaultError as e:
+        sys.exit(f"Error accessing task or memory: {e}")
+    except Exception as e:
+        sys.exit(f"Unexpected error: {e}")
+
+if __name__ == "__main__":
+    main()
-- 
2.25.1

Re: [PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[SeongJae Park]

On Fri, 30 May 2025 13:58:55 +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 0x7fc988181000
> PID: 1 Comm: systemd mm: 0xffff8d22c4089700
> RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
> RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
> Page Address:    0xfffff93905664e00
> Page Flags:      PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
>                  PG_private|PG_reported|PG_has_hwpoisoned
> Page Size:       4096
> Page PFN:        0x159938
> Page Physical:   0x159938000
> Page Virtual:    0xffff8d2319938000
> Page Refcount:   37
> Page Mapcount:   7
> Page Index:      0x0
> Page Memcg Data: 0xffff8d23203ff500
> Memcg Name:      init.scope
> Memcg Path:      /sys/fs/cgroup/memory/init.scope

As reported to the previous version, I show below on my test.

Memcg Name:      unknown
Memcg Path:      Unexpected error: 'struct kernfs_node' has no member 'parent'

I know you explained it is an issue of drgn version on my setup, as a reply to
my previous report.  But, could you please make the output more easy to
understand the problem?  No strong opinion, though.

> Page Mapping:    0xffff8d23062a12a8
> Page Anon/File:  File
> Page VMA:        0xffff8d22e06e0e40
> VMA Start:       0x7fc988181000
> VMA End:         0x7fc988185000
> This page is part of a compound page.
> This page is the head page of a compound page.
> Head Page:       0xfffff93905664e00
> Compound Order:  2
> Number of Pages: 4
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Tested-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[Stephen Brennan]

Ye Liu <ye.liu@linux.dev> writes:
> 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 0x7fc988181000
> PID: 1 Comm: systemd mm: 0xffff8d22c4089700
> RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
> RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
> Page Address:    0xfffff93905664e00
> Page Flags:      PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
>                  PG_private|PG_reported|PG_has_hwpoisoned
> Page Size:       4096
> Page PFN:        0x159938
> Page Physical:   0x159938000
> Page Virtual:    0xffff8d2319938000
> Page Refcount:   37
> Page Mapcount:   7
> Page Index:      0x0
> Page Memcg Data: 0xffff8d23203ff500
> Memcg Name:      init.scope
> Memcg Path:      /sys/fs/cgroup/memory/init.scope
> Page Mapping:    0xffff8d23062a12a8
> Page Anon/File:  File
> Page VMA:        0xffff8d22e06e0e40
> VMA Start:       0x7fc988181000
> VMA End:         0x7fc988185000
> This page is part of a compound page.
> This page is the head page of a compound page.
> Head Page:       0xfffff93905664e00
> Compound Order:  2
> Number of Pages: 4
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Reviewed-by: Stephen Brennan <stephen.s.brennan@oracle.com>

>
> Changes in v5:
> - Use platform-aware word-size reads instead of raw byte access.
> - Replace Object() with drgn.cast() for type safety.
> - Better handle memcg flags and error cases.
> - Exit on fatal errors with sys.exit().
> - Remove 'User Virtual Address'.
> - Link to v4:https://lore.kernel.org/all/20250528091543.355386-1-ye.liu@linux.dev/
>
> Changes in v4:
> - Add error and exception handling.
> - Adjust the way to obtain PAGE_SIZE.
> - Fix the acquisition of memcg.
> - Link to v3:https://lore.kernel.org/all/20250423014850.344501-1-ye.liu@linux.dev/
>
> 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 | 169 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 174 insertions(+)
>  create mode 100644 tools/mm/show_page_info.py
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0cb9e55021cb..3cbd46bf1eab 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -18726,6 +18726,11 @@ 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 100644
> index 000000000000..c46d8ea283d7
> --- /dev/null
> +++ b/tools/mm/show_page_info.py
> @@ -0,0 +1,169 @@
> +#!/usr/bin/env drgn
> +# SPDX-License-Identifier: GPL-2.0-only
> +# Copyright (C) 2025 Ye Liu <liuye@kylinos.cn>
> +
> +import argparse
> +import sys
> +from drgn import Object, FaultError, PlatformFlags, cast
> +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.
> +"""
> +
> +def format_page_data(page):
> +    """
> +    Format raw page data into a readable hex dump with "RAW:" prefix.
> +
> +    :param page: drgn.Object instance representing the page.
> +    :return: Formatted string of memory contents.
> +    """
> +    try:
> +        address = page.value_()
> +        size = prog.type("struct page").size
> +
> +        if prog.platform.flags & PlatformFlags.IS_64_BIT:
> +            word_size = 8
> +        else:
> +            word_size = 4
> +        num_words = size // word_size
> +
> +        values = []
> +        for i in range(num_words):
> +            word_address = address + i * word_size
> +            word = prog.read_word(word_address)
> +            values.append(f"{word:0{word_size * 2}x}")
> +
> +        lines = [f"RAW: {' '.join(values[i:i + 4])}" for i in range(0, len(values), 4)]
> +
> +        return "\n".join(lines)
> +
> +    except FaultError as e:
> +        return f"Error reading memory: {e}"
> +    except Exception as e:
> +        return f"Unexpected error: {e}"
> +
> +def get_memcg_info(page):
> +    """Retrieve memory cgroup information for a page."""
> +    try:
> +        MEMCG_DATA_OBJEXTS = prog.constant("MEMCG_DATA_OBJEXTS").value_()
> +        MEMCG_DATA_KMEM = prog.constant("MEMCG_DATA_KMEM").value_()
> +        mask = prog.constant('__NR_MEMCG_DATA_FLAGS').value_() - 1
> +        memcg_data = page.memcg_data.read_()
> +        if memcg_data & MEMCG_DATA_OBJEXTS:
> +            slabobj_ext = cast("struct slabobj_ext *", memcg_data & ~mask)
> +            memcg = slabobj_ext.objcg.memcg.value_()
> +        elif memcg_data & MEMCG_DATA_KMEM:
> +            objcg = cast("struct obj_cgroup *", memcg_data & ~mask)
> +            memcg = objcg.memcg.value_()
> +        else:
> +            memcg = cast("struct mem_cgroup *", memcg_data & ~mask)
> +
> +        if memcg.value_() == 0:
> +            return "none", "/sys/fs/cgroup/memory/"
> +        cgrp = memcg.css.cgroup
> +        return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
> +    except FaultError as e:
> +        return "unknown", f"Error retrieving memcg info: {e}"
> +    except Exception as e:
> +        return "unknown", f"Unexpected error: {e}"
> +
> +def show_page_state(page, addr, mm, pid, task):
> +    """Display detailed information about a page."""
> +    try:
> +        print(f'PID: {pid} Comm: {task.comm.string_().decode()} mm: {hex(mm)}')
> +        try:
> +            print(format_page_data(page))
> +        except FaultError as e:
> +            print(f"Error reading page data: {e}")
> +        fields = {
> +            "Page Address": hex(page.value_()),
> +            "Page Flags": decode_page_flags(page),
> +            "Page Size": prog["PAGE_SIZE"].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.__folio_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"
> +
> +        try:
> +            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_())
> +        except FaultError as e:
> +            fields["Page VMA"] = "Unavailable"
> +            fields["VMA Start"] = "Unavailable"
> +            fields["VMA End"] = "Unavailable"
> +            print(f"Error retrieving VMA information: {e}")
> +
> +        # 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.")
> +    except FaultError as e:
> +        print(f"Error accessing page state: {e}")
> +    except Exception as e:
> +        print(f"Unexpected error: {e}")
> +
> +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:
> +        sys.exit(f"Error: Invalid virtual address format: {args.vaddr}")
> +
> +    try:
> +        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:
> +            sys.exit(f"Address {hex(vaddr)} is not mapped.")
> +    except FaultError as e:
> +        sys.exit(f"Error accessing task or memory: {e}")
> +    except Exception as e:
> +        sys.exit(f"Unexpected error: {e}")
> +
> +if __name__ == "__main__":
> +    main()
> -- 
> 2.25.1

Re: [PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[Stephen Brennan]

SeongJae Park <sj@kernel.org> writes:
> On Fri, 30 May 2025 13:58:55 +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 0x7fc988181000
>> PID: 1 Comm: systemd mm: 0xffff8d22c4089700
>> RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
>> RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
>> Page Address:    0xfffff93905664e00
>> Page Flags:      PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
>>                  PG_private|PG_reported|PG_has_hwpoisoned
>> Page Size:       4096
>> Page PFN:        0x159938
>> Page Physical:   0x159938000
>> Page Virtual:    0xffff8d2319938000
>> Page Refcount:   37
>> Page Mapcount:   7
>> Page Index:      0x0
>> Page Memcg Data: 0xffff8d23203ff500
>> Memcg Name:      init.scope
>> Memcg Path:      /sys/fs/cgroup/memory/init.scope
>
> As reported to the previous version, I show below on my test.
>
> Memcg Name:      unknown
> Memcg Path:      Unexpected error: 'struct kernfs_node' has no member 'parent'
>
> I know you explained it is an issue of drgn version on my setup, as a reply to
> my previous report.  But, could you please make the output more easy to
> understand the problem?  No strong opinion, though.

This is an interesting issue.

The cgroup helpers in drgn were broken by the name change of
kernfs_node.parent to kernfs_node.__parent in Linux 6.15. This was fixed
in drgn promptly, and the fix is included in drgn's 0.0.31 release. If
you use that, the error should go away. In essence, 0.0.31 was the first
drgn version to support Linux 6.15.

However, there's no general way to catch any drgn error and determine
that that drgn doesn't support your kernel version (yet). The code could
be updated for this specific issue, but it wouldn't really fix the
general problem. I think drgn needs to include an (INFORMATIONAL ONLY)
set of kernel versions that it has been tested on. Then, you could use
that in a script to print a warning (or add it to your general purpose
error handling). I'll look into adding this.

This is itself a corner case for committing drgn scripts in the kernel.
Omar does a really excellent job with running tests on the -rc's and
finding broken helpers promptly -- usually well ahead of the kernel
release. But even then, there can be a delay from the fix to the next
drgn release. The more that you rely on drgn's helpers for a script that
you distribute in the kernel, the more likely that it will periodically
break, and the in-tree version wouldn't work until the newer drgn
version is released.

I don't have a solution for *that*, but it's something to consider when
deciding whether to include a script in drgn's contrib/ directory, versus
in the kernel.

Stephen

Re: [PATCH v5] tools/mm: Add script to display page state for a given PID and VADDR

[SeongJae Park]

On Fri, 30 May 2025 15:15:15 -0700 Stephen Brennan <stephen.s.brennan@oracle.com> wrote:

> SeongJae Park <sj@kernel.org> writes:
> > On Fri, 30 May 2025 13:58:55 +0800 Ye Liu <ye.liu@linux.dev> wrote:
[...]
> > As reported to the previous version, I show below on my test.
> >
> > Memcg Name:      unknown
> > Memcg Path:      Unexpected error: 'struct kernfs_node' has no member 'parent'
> >
> > I know you explained it is an issue of drgn version on my setup, as a reply to
> > my previous report.  But, could you please make the output more easy to
> > understand the problem?  No strong opinion, though.
> 
> This is an interesting issue.
> 
> The cgroup helpers in drgn were broken by the name change of
> kernfs_node.parent to kernfs_node.__parent in Linux 6.15. This was fixed
> in drgn promptly, and the fix is included in drgn's 0.0.31 release. If
> you use that, the error should go away. In essence, 0.0.31 was the first
> drgn version to support Linux 6.15.

FYI, I'm using drgn package on Debian 12, which says

    $ drgn --version
    drgn 0.0.30+82.ge2b60e4b (using Python 3.11.2, elfutils 0.188, without libkdumpfile)

Also I run a kernel built from damon/next[1], which is based on 6.15-rc6.

> 
> However, there's no general way to catch any drgn error and determine
> that that drgn doesn't support your kernel version (yet). The code could
> be updated for this specific issue, but it wouldn't really fix the
> general problem. I think drgn needs to include an (INFORMATIONAL ONLY)
> set of kernel versions that it has been tested on. Then, you could use
> that in a script to print a warning (or add it to your general purpose
> error handling).

Sounds like a nice plan!

> I'll look into adding this.

Thank you!  I'm not urgent or having a real problem with this at the moment,
though.  So, please take your time and fun!

> 
> This is itself a corner case for committing drgn scripts in the kernel.
> Omar does a really excellent job with running tests on the -rc's and
> finding broken helpers promptly -- usually well ahead of the kernel
> release. But even then, there can be a delay from the fix to the next
> drgn release. The more that you rely on drgn's helpers for a script that
> you distribute in the kernel, the more likely that it will periodically
> break, and the in-tree version wouldn't work until the newer drgn
> version is released.
> 
> I don't have a solution for *that*, but it's something to consider when
> deciding whether to include a script in drgn's contrib/ directory, versus
> in the kernel.

Makes sense, thank you for sharing your wise thoughts.  This is very helpful to
me.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees


Thanks,
SJ

[...]