Re: [PATCH v2] mm/vmstat: Add order's information for extfrag_index and unusable_index

[Andrew Morton]

On Thu, 29 Feb 2024 22:14:43 +0800 Hao Ge <gehao@xxxxxxxxxx> wrote:

> Current cat /sys/kernel/debug/extfrag/extfrag_index and
> /sys/kernel/debug/extfrag/unusable_index is not friendly to userspace.
> 
> We should add order's information so that users can clearly understand
> the situation of each order at a glance like pagetypeinfo.
> 
> before:
> cat /sys/kernel/debug/extfrag/extfrag_index:
> Node 0, zone    DMA32  ...... ...... ...... ......
> Node 0, zone   Normal  ...... ...... ...... ......
> 
> cat /sys/kernel/debug/extfrag/unusable_index:
> Node 0, zone    DMA32 ..... ..... ..... .....
> Node 0, zone   Normal ..... ..... ..... .....
> 
> after:
> cat /sys/kernel/debug/extfrag/extfrag_index:
> Extfrag index at order:       0      1      2      3
> Node 0, zone        DMA  ...... ...... ...... ......
> Node 0, zone     Normal  ...... ...... ...... ......
> 
> cat /sys/kernel/debug/extfrag/unusable_index:
> Unusable index at order:     0     1     2     3
> Node 0, zone         DMA ..... ..... ..... .....
> Node 0, zone      Normal ..... ..... ..... .....
> 

This may break existing parsers of this file.

And that would be allowed if these files were under debugfs.  But
they're under sysfs/debug, where the rules are less clear.

Still, it's unclear to me that the benefit is worth this risk.  What do
others think?