Re: [PATCH v3 1/4] mm/zswap: Make shrink_worker writeback cursor per-memcg

[Nhat Pham]

On Tue, May 26, 2026 at 4:46 AM Hao Jia <jiahao.kernel@xxxxxxxxx> wrote:
>
> From: Hao Jia <jiahao1@xxxxxxxxxxx>
>
> The zswap background writeback worker shrink_worker() uses a global
> cursor zswap_next_shrink, protected by zswap_shrink_lock, to round-robin
> across the online memcgs under root_mem_cgroup.
>
> Proactive writeback also wants a similar per-memcg cursor that is
> scoped to the specified memcg, so that repeated invocations against
> the same memcg make forward progress across its descendant memcgs
> instead of restarting from the first child memcg each time.
>
> Naturally, group the cursor and its protecting spinlock into a
> zswap_wb_iter struct, and make it a member of struct mem_cgroup to
> realize per-memcg cursor management. Accordingly, shrink_worker() now
> uses the lock and cursor in root_mem_cgroup->zswap_wb_iter.
>
> Because the cursor is now per-memcg, the offline cleanup must visit
> every ancestor that could be holding a reference to the dying memcg.
> Factor out __zswap_memcg_offline_cleanup() and walk from dead_memcg up
> to the root.
>
> No functional change intended for shrink_worker().

LGTM, if the memcg maintainers are happy with the overhead.

Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>