Re: [PATCH 2/6] mm/zswap: invalidate zswap entry when swap entry free

Nhat Pham
2024-02-01T20:56:32Z

On Thu, Feb 1, 2024 at 7:50 AM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> During testing I found there are some times the zswap_writeback_entry()
> return -ENOMEM, which is not we expected:
>
> bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=count()}'
> @[-12]: 1563
> @[0]: 277221
>
> The reason is that __read_swap_cache_async() return NULL because
> swapcache_prepare() failed. The reason is that we won't invalidate
> zswap entry when swap entry freed to the per-cpu pool, these zswap
> entries are still on the zswap tree and lru list.
>
> This patch moves the invalidation ahead to when swap entry freed
> to the per-cpu pool, since there is no any benefit to leave trashy
> zswap entry on the tree and lru list.
>
> With this patch:
> bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=count()}'
> @[0]: 259744

Nice!
Reviewed-by: Nhat Pham <nphamcs@gmail.com>