Re: [RFC PATCH v2 0/4] mm/zsmalloc: reduce zs_free() latency on swap release path

[Kairui Song]

On Thu, Apr 30, 2026 at 3:43 PM Wenchao Hao <haowenchao22@xxxxxxxxx> wrote:
> The data I shared earlier was class_idx-in-obj only — no
> deferred freeing at all.
>
> > I couldn't immediately tell by looking at this vs. the cover letter.  I wonder
> > what portion of the improvement comes from the deferred freeing?
>
> On top of that, we added deferred freeing in the zsmalloc
> layer (per-cpu page-pool based buffer swap + WQ_UNBOUND
> drain worker). With both class_idx + deferred:
>
> Test 1: concurrent munmap (256MB/process, RPi 4B):
>
>   mode      Base       Deferred    Speedup
>   single    56.2ms     17.2ms      3.27x
>   multi 3p  153.2ms    51.5ms      2.97x
>
> Test 2: single process munmap (various sizes):
>
>   size      Base       Deferred    Speedup
>   64MB      15.0ms     4.3ms       3.47x
>   128MB     28.7ms     8.5ms       3.37x
>   192MB     43.2ms     13.0ms      3.32x
>   256MB     57.0ms     17.3ms      3.30x
>   512MB     114.4ms    38.5ms      2.97x

Hi Wenchao,

One concern here is that the total amount of work is unchanged. I mean
you observe speed up because you offloaded the work to an async
worker. But when under pressure these workers could be a larger
burden. Is it possible for you to measure that part too?