[PATCH v2 0/1] mm/page_alloc: dynamic min_free_kbytes adjustment

[wujing <realwujing@qq.com>]

This is v2 of the auto-tuning patch, addressing feedback from Andrew Morton
and Matthew Wilcox.

## Responses to Andrew Morton's feedback:

> "But no attempt to reduce it again after the load spike has gone away."

v2 implements a decay mechanism: min_free_kbytes automatically reduces by 5%
every 5 minutes after being increased. However, it stops at 1.2x the initial
value rather than returning to baseline, ensuring the system "remembers"
previous pressure patterns.

> "Probably this should be selectable and tunable via a kernel boot parameter
> or a procfs tunable."

Per Matthew Wilcox's preference to avoid new tunables, v2 implements an
algorithm designed to work automatically without configuration. The parameters
(50% increase, 5% decay, 10s debounce) are chosen to be responsive yet stable.

> "Can I suggest that you engage with [the networking people]? netdev@"

Done - netdev@ is now CC'd on this v2 submission.

## Responses to Matthew Wilcox's feedback:

> "Is doubling too aggressive? Would an increase of, say, 10% or 20% be more
> appropriate?"

v2 uses a 50% increase (compromise between responsiveness and conservatism).
20% felt too slow for burst traffic scenarios based on our observations.

> "Do we have to wait for failure before increasing? Could we schedule the
> increase for when we get to within, say, 10% of the current limit?"

We considered proactive monitoring but concluded it would add overhead and
complexity. The debounce mechanism (10s) ensures we don't thrash while still
being reactive.

> "Hm, how would we do that? Automatically decay by 5%, 300 seconds after
> increasing; then schedule another decay for 300 seconds after that..."

Exactly as you suggested! v2 implements this decay chain. The only addition
is stopping at 1.2x baseline to preserve learning.

> "Ugh, please, no new tunables. Let's just implement an algorithm that works."

Agreed - v2 has zero new tunables.

## Changes in v2:
- Reduced aggressiveness: +50% increase instead of doubling
- Added debounce: Only trigger once per 10 seconds to prevent storms
- Added decay: Automatically reduce by 5% every 5 minutes
- Preserve learning: Decay stops at 1.2x initial value, not baseline
- Engaged networking community (netdev@)

Thanks for the thoughtful reviews!

wujing (1):
  mm/page_alloc: auto-tune min_free_kbytes on atomic allocation failure

 mm/page_alloc.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

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2.39.5