Re: [PATCH v2 2/3] mm/page_owner: add print_mode filter

[zhen.ni]

在 2026/4/28 21:20, Zi Yan 写道:
> On 27 Apr 2026, at 23:36, zhen.ni wrote:
>
> > 在 2026/4/27 23:43, Zi Yan 写道:
> > > On 19 Apr 2026, at 11:55, Zhen Ni wrote:
> > >
> > > > Add print_mode functionality to reduce page_owner output size by
> > > > printing only the stack handle instead of the full stack trace.
> > > >
> > > > Example output with print_mode enabled:
> > > >     Page allocated via order 0, mask 0x42800(GFP_NOWAIT|__GFP_COMP),
> > > >     pid 1, tgid 1 (systemd), ts 349667370 ns
> > > >     PFN 0xa00a2 type Unmovable Block 1280 type Unmovable
> > > >     Flags 0x33fffe0000004124(referenced|lru|active|private|node=3|zone=0|
> > > > lastcpupid=0x1ffff)
> > > >     handle: 17432583
> > > >     Charged to memcg /
> > > >
> > > > Print mode significantly reduces output size while preserving all
> > > > other page allocation information. The correspondence between handles
> > > > and stack traces can be obtained through the show_stacks_handles interface.
> > > >
> > > > Link: https://lore.kernel.org/linux-mm/20260417154638.22370-3-zhen.ni@xxxxxxxxxxxx/
> > > > Suggested-by: Zi Yan <ziy@xxxxxxxxxx>
> > > > Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>
> > > > ---
> > > >
> > > > Changes in v2:
> > > > - Renamed from 'compact mode' to 'print_mode' for better clarity
> > > > - Use enum values (0=full_stack, 1=stack_handle) instead of boolean
> > > > - Update debugfs filename from 'compact' to 'print_mode'
> > > > ---
> > > >    mm/page_owner.c | 28 +++++++++++++++++++++++++++-
> > > >    1 file changed, 27 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/page_owner.c b/mm/page_owner.c
> > > > index 5884d883837e..6d87b6948cfa 100644
> > > > --- a/mm/page_owner.c
> > > > +++ b/mm/page_owner.c
> > > > @@ -590,7 +590,13 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
> > > >    			migratetype_names[pageblock_mt],
> > > >    			&page->flags);
> > > >
> > > > -	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
> > > > +	/* Print mode: full stack or stack handle */
> > > > +	if (READ_ONCE(owner_filter.print_mode) == PAGE_OWNER_PRINT_STACK_HANDLE) {
> > > > +		ret += scnprintf(kbuf + ret, count - ret,
> > > > +				"handle: %d\n", handle);
> > > > +	} else {
> > > > +		ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
> > > > +	}
> > > >    	if (ret >= count)
> > > >    		goto err;
> > > >
> > > > @@ -985,6 +991,24 @@ static int page_owner_threshold_set(void *data, u64 val)
> > > >    DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
> > > >    			&page_owner_threshold_set, "%llu");
> > > >
> > > > +static int page_owner_print_mode_get(void *data, u64 *val)
> > > > +{
> > > > +	*val = READ_ONCE(owner_filter.print_mode);
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static int page_owner_print_mode_set(void *data, u64 val)
> > > > +{
> > > > +	if (val > PAGE_OWNER_PRINT_STACK_HANDLE)
> > > > +		return -EINVAL;
> > > > +	WRITE_ONCE(owner_filter.print_mode, val);
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +DEFINE_SIMPLE_ATTRIBUTE(page_owner_print_mode_fops,
> > > > +			&page_owner_print_mode_get,
> > > > +			&page_owner_print_mode_set, "%lld");
> > > > +
> > > >
> > > >    static int __init pageowner_init(void)
> > > >    {
> > > > @@ -998,6 +1022,8 @@ static int __init pageowner_init(void)
> > > >    	debugfs_create_file("page_owner", 0400, NULL, NULL, &page_owner_fops);
> > > >
> > > >    	filter_dir = debugfs_create_dir("page_owner_filter", NULL);
> > > > +	debugfs_create_file("print_mode", 0600, filter_dir, NULL,
> > > > +			    &page_owner_print_mode_fops);
> > > >
> > > >    	dir = debugfs_create_dir("page_owner_stacks", NULL);
> > > >    	debugfs_create_file("show_stacks", 0400, dir,
> > > > --
> > > > 2.20.1
> > >
> > > I think it is more user-friendly to use “full_stack” and “stack_handle”
> > > instead of 0 and 1. You can refer to [1] to sysfs_match_string() to
> > > do that. I was testing the interface, but needed to look at your code
> > > to know which print_mode I am using. ;)
> > >
> > >
> > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/mm/huge_memory.c?h=mm-everything#n380
> >
> > Thanks for the suggestion!
> >
> > I considered using "full_stack" and "stack_handle" strings, but
> > I think the numeric values (0/1) are more concise and easier to type
> > for users.
>
> I disagree. It is hard for user to know what the current print mode
> is and what available modes are. 0 or 1 is usually for boolean input.
>
> Something like:
> [full_stack] stack_handle
> full_stack [stack_handle]
>
> is much easier for user to read and use.
The string-based interface is more user-friendly

I'll switch to using string values "full_stack" and "stack_handle"
with sysfs_match_string() in v4, implementing the show function to
 display them with [] brackets around the current selection.
> > The v3 documentation will clarify the meaning:
> > - 0 (default): Print full stack traces
> > - 1: Print only stack handles
> >
> > Do you think this is sufficient, or would you still prefer using
> > string values instead?
> >
> >
> > > Best Regards,
> > > Yan, Zi
> > Best regards,
> > Zhen
>
>
> Best Regards,
> Yan, Zi
Best regards,
Zhen