Re: [RFC PATCH] zram: support asynchronous GC for lazy slot freeing

[Sergey Senozhatsky]

On (26/04/14 13:49), Xueyuan Chen wrote:
> On Sun, Apr 12, 2026 at 07:48:48PM +0800, Kairui Song wrote:
> [...]
> >What is making this slot_free so costly? zs_free?
> 
> Yes, I've captured some perf data on RK3588 cpu2: 
> 
>   -    3.79%     0.42%  zram  [zram]  [k] slot_free
>      - 89.04% slot_free
>         - 65.40% zs_free
>            + 77.29% free_zspage
>            + 21.75% kmem_cache_free
>              0.68% __kern_my_cpu_offset
>         + 13.19% _raw_spin_unlock
>         + 4.86% _raw_read_unlock
>           4.75% obj_free
>         + 4.72% _raw_read_lock
>           3.64% fix_fullness_group
>         + 2.02% _raw_spin_lock
>         + 1.31% kmem_cache_free
> 
> It's clear that zs_free is the primary hotspot, accounting for ~65.40%
> of the total slot_free cycles. Beyond that, have some read and spin lock
> in slot_free.

Just a random thought, if zs_free() is costly then it likely also affects
zswap, which makes me wonder if doing something on the zsmalloc side is a
"batter" way forward.