linux-kernel - Re: [PATCH v2] mm/vmstat: Add order's information for extfrag_index and unusable

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Message-Id: <20240229104013.5ed8c1ca9c2dbd0bd5fb571f@linux-foundation.org>
Date: Thu, 29 Feb 2024 10:40:13 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Hao Ge <gehao@...inos.cn>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, gehao618@....com
Subject: Re: [PATCH v2] mm/vmstat: Add order's information for extfrag_index
 and unusable_index

On Thu, 29 Feb 2024 22:14:43 +0800 Hao Ge <gehao@...inos.cn> 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?