Re: [PATCH] mm: add Adaptive Memory Pressure Signaling (AMPRESS)

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Mar 02, 2026 at 12:45:33AM -0300, Andre Ramos wrote:
> Introduce /dev/ampress, a bidirectional fd-based interface for
> cooperative memory reclaim between the kernel and userspace.
> 
> Userspace processes open /dev/ampress and block on read() to receive
> struct ampress_event notifications carrying a graduated urgency level
> (LOW/MEDIUM/HIGH/FATAL), the NUMA node of the pressure source, and a
> suggested reclaim target in KiB. After freeing memory the process
> issues AMPRESS_IOC_ACK to close the feedback loop.
> 
> The feature hooks into balance_pgdat() in mm/vmscan.c, mapping the
> kswapd scan priority to urgency bands:
>   priority 10-12 -> LOW
>   priority  7-9  -> MEDIUM
>   priority  4-6  -> HIGH
>   priority  1-3  -> FATAL

The scan priority is not a good proxy for pressure. We actually export
reclaim efficiency-based pressure levels like this in memory cgroups
v1, but they're being deprecated[1] in favor of PSI [2].

What are you trying to accomplish?

[1] 340afb8027fa ("memcg: initiate deprecation of pressure_level")
[2] Documentation/accounting/psi.rst