On Fri Sep 4, 2026 at 12:20 PM CEST, Hui Zhu wrote: > From: Hui Zhu <[email protected]> > > BPF programs can observe memory pressure on a cgroup (e.g. refault > stats via bpf_mem_cgroup_page_state()), but cannot act on it: > triggering reclaim on a chosen cgroup requires writing to > memory.reclaim, which BPF cannot do. This series adds > bpf_proactive_reclaim(), a sleepable kfunc performing one proactive > reclaim pass on a target memcg, so when and how hard to reclaim is > BPF policy rather than hard-coded thresholds. > > The kfunc is restricted to BPF_PROG_TYPE_SYSCALL so that reclaim > always runs in a clean process context: generic sleepable programs > may execute with filesystem locks held or in NOFS/NOIO contexts, > where the reclaim path could deadlock in filesystem shrinkers. The > bpf_wq and task_work callbacks of a SYSCALL program keep its program > type and run in process context, so reclaim work can still be queued > asynchronously through them, as the selftest does with bpf_wq. > > The use case we are looking at is protecting high-priority workloads: > a BPF program monitors the state of a high-priority cgroup and, when > it degrades (e.g. PSI rises or refaults increase, as in the > selftest), asynchronously reclaims memory from low-priority cgroups > via bpf_wq and bpf_proactive_reclaim(), giving the pressured cgroup > more free pages. > > Another use case: several vendor-maintained kernels carry private > implementations that trigger asynchronous reclaim when a memcg enters > a certain state. These exist for historical and partly psychological > reasons, but the underlying demand is real. We expect BPF-driven > proactive reclaim, combined with the BPF hooks for the memory > controller currently under discussion and development, to serve these > needs in mainline, reducing kernel fragmentation and improving kernel > maintainability.
>From BPF perspective this looks ok to me. I saw you dropped the swappiness argument, what happened there? I thought we agreed to just include it in the kfunc now. Did something change?
