On Mon, May 11, 2026 at 06:51:46PM +0800, Hao Jia <jiahao.kernel@gmail.com> wrote:
> From: Hao Jia <jiahao1@lixiang.com>
> 
> Zswap currently writes back pages to backing swap devices reactively,
> triggered either by memory pressure via the shrinker or by the pool
> reaching its size limit. However, this reactive approach makes writeback
> timing indeterminate and can disrupt latency-sensitive workloads when
> eviction happens to coincide with a critical execution window.
> 
> Furthermore, in certain scenarios, it is desirable to trigger writeback
> in advance to free up memory. For example, users may want to prepare for
> an upcoming memory-intensive workload by flushing cold memory to the
> backing storage when the system is relatively idle.

I can imagine the zswap writeout can come at the least possible
moment...

> To address these issues, this patch series introduces a per-cgroup
> interface that allows users to proactively write back cold compressed
> pages from zswap to the backing swap device.

...but I see this series is not only per-cgroup proactive reclaim but
it's also age-based reclaim.

The per-cg consumption and limits (and regular memory reclaim) are all
measured in sizes. This age-based invocations don't seem commensurable
(e.g. how would users in practice determine what is the desired input to
here).

Could you explain more reasoning behind this design?

Thanks,
Michal