Re: [LSF/MM/BPF TOPIC][RFC PATCH v4 00/27] Private Memory Nodes (w/ Compressed RAM)

Gregory Price
2026-05-05T07:45:56Z

On Mon, May 04, 2026 at 06:38:54PM +0530, Arun George/Arun George wrote:
> On 29-04-2026 07:12 pm, Gregory Price wrote:
>
> But I see this 'write budget' (budget in terms of number of write
> operations that can be handled by the device, not capacity) to be
> provided by the device in control plane; not by the workloads in the host.
>

In the scenario i'm talking about, a "write budget" is defined as a
number of pages that are allows to be mapped writable in the page
tables at any given time.

> 1) We can modulate the write budget depending on the actual
> compressibility in the device (and so workloads data). We don't have to
> do estimation based on the workloads.
>

Barring the device causing backpressure to increase latency and slow
down writes, modulating a write budget doesn't actually do anything
useful. Once a page is mapped writable - the CPU is free to write to
that page uncontended.

I think a write budget is "doable" but maybe a bit optimistic for an
MVP. There are many corner cases to handle, and I would prefer to see
that as an experimental optimization.

> 2) We don't have to do the capacity modulation - as in ballooning or
> shrinker.
>

You still need capacity modulation in some way to respond to drops in
compression ratio.

~Gregory