Update page_owner documentation including the new page_owner_stacks
feature to show how it can be used.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 Documentation/mm/page_owner.rst | 44 +++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
index 62e3f7ab23cc..bcde81bf0902 100644
--- a/Documentation/mm/page_owner.rst
+++ b/Documentation/mm/page_owner.rst
@@ -24,6 +24,11 @@ fragmentation statistics can be obtained through gfp flag information of
 each page. It is already implemented and activated if page owner is
 enabled. Other usages are more than welcome.
 
+It can also be used to show all the stacks and their outstanding
+allocations, which gives us a quick overview of where the memory is going
+without the need to screen through all the pages and match the allocation
+and free operation.
+
 page owner is disabled by default. So, if you'd like to use it, you need
 to add "page_owner=on" to your boot cmdline. If the kernel is built
 with page owner and page owner is disabled in runtime due to not enabling
@@ -68,6 +73,45 @@ Usage
 
 4) Analyze information from page owner::
 
+	cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt
+	cat stacks.txt
+	 prep_new_page+0xa9/0x120
+	 get_page_from_freelist+0x7e6/0x2140
+	 __alloc_pages+0x18a/0x370
+	 new_slab+0xc8/0x580
+	 ___slab_alloc+0x1f2/0xaf0
+	 __slab_alloc.isra.86+0x22/0x40
+	 kmem_cache_alloc+0x31b/0x350
+	 __khugepaged_enter+0x39/0x100
+	 dup_mmap+0x1c7/0x5ce
+	 copy_process+0x1afe/0x1c90
+	 kernel_clone+0x9a/0x3c0
+	 __do_sys_clone+0x66/0x90
+	 do_syscall_64+0x7f/0x160
+	 entry_SYSCALL_64_after_hwframe+0x6c/0x74
+	stack_count: 234
+	...
+	...
+	echo 7000 > /sys/kernel/debug/page_owner_stacks/set_threshold > stacks_7000.txt
+	cat stacks_7000.txt
+	 prep_new_page+0xa9/0x120
+	 get_page_from_freelist+0x7e6/0x2140
+	 __alloc_pages+0x18a/0x370
+	 alloc_pages_mpol+0xdf/0x1e0
+	 folio_alloc+0x14/0x50
+	 filemap_alloc_folio+0xb0/0x100
+	 page_cache_ra_unbounded+0x97/0x180
+	 filemap_fault+0x4b4/0x1200
+	 __do_fault+0x2d/0x110
+	 do_pte_missing+0x4b0/0xa30
+	 __handle_mm_fault+0x7fa/0xb70
+	 handle_mm_fault+0x125/0x300
+	 do_user_addr_fault+0x3c9/0x840
+	 exc_page_fault+0x68/0x150
+	 asm_exc_page_fault+0x22/0x30
+	stack_count: 8248
+	...
+
 	cat /sys/kernel/debug/page_owner > page_owner_full.txt
 	./page_owner_sort page_owner_full.txt sorted_page_owner.txt
 
-- 
2.43.0

On Mon, 12 Feb 2024 at 23:29, Oscar Salvador <osalvador@suse.de> wrote:
>
> Update page_owner documentation including the new page_owner_stacks
> feature to show how it can be used.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
>  Documentation/mm/page_owner.rst | 44 +++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>
> diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
> index 62e3f7ab23cc..bcde81bf0902 100644
> --- a/Documentation/mm/page_owner.rst
> +++ b/Documentation/mm/page_owner.rst
> @@ -24,6 +24,11 @@ fragmentation statistics can be obtained through gfp flag information of
>  each page. It is already implemented and activated if page owner is
>  enabled. Other usages are more than welcome.
>
> +It can also be used to show all the stacks and their outstanding
> +allocations, which gives us a quick overview of where the memory is going
> +without the need to screen through all the pages and match the allocation
> +and free operation.
> +
>  page owner is disabled by default. So, if you'd like to use it, you need
>  to add "page_owner=on" to your boot cmdline. If the kernel is built
>  with page owner and page owner is disabled in runtime due to not enabling
> @@ -68,6 +73,45 @@ Usage
>
>  4) Analyze information from page owner::
>
> +       cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt
> +       cat stacks.txt
> +        prep_new_page+0xa9/0x120
> +        get_page_from_freelist+0x7e6/0x2140
> +        __alloc_pages+0x18a/0x370
> +        new_slab+0xc8/0x580
> +        ___slab_alloc+0x1f2/0xaf0
> +        __slab_alloc.isra.86+0x22/0x40
> +        kmem_cache_alloc+0x31b/0x350
> +        __khugepaged_enter+0x39/0x100
> +        dup_mmap+0x1c7/0x5ce
> +        copy_process+0x1afe/0x1c90
> +        kernel_clone+0x9a/0x3c0
> +        __do_sys_clone+0x66/0x90
> +        do_syscall_64+0x7f/0x160
> +        entry_SYSCALL_64_after_hwframe+0x6c/0x74
> +       stack_count: 234
> +       ...
> +       ...
> +       echo 7000 > /sys/kernel/debug/page_owner_stacks/set_threshold > stacks_7000.txt

I think this example command is wrong.

On Tue, Feb 13, 2024 at 09:45:28AM +0100, Marco Elver wrote:
> On Mon, 12 Feb 2024 at 23:29, Oscar Salvador <osalvador@suse.de> wrote:
> > +       echo 7000 > /sys/kernel/debug/page_owner_stacks/set_threshold > stacks_7000.txt
> 
> I think this example command is wrong.

Yes, it is, I will correct that in the next spin.

thanks!

-- 
Oscar Salvador
SUSE Labs