Re: [RFC PATCH 0/2] mm: zsmalloc: make shrinker compaction budget-aware

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (26/08/07 18:57), Xueyuan Chen wrote:
> Hi Sergey,
> 
> Here is some additional data:
> 
> I used the following definitions:
>   compactable ratio = freeable_pages / total_pages
>   memory reclaimed  = pages_freed * PAGE_SIZE
> 
> freeable_pages is the estimate before compaction, based on the same
> calculation as zs_shrinker_count(), while pages_freed is the actual
> number of backing pages released.
> 
> There were 264 callbacks in the trace:
>   callback elapsed time:
>     median:    5.77 ms
>     p95:      55.82 ms
>     maximum: 271.36 ms
> 
>   compactable ratio before compaction:
>     median:   0.32%
>     p95:      2.86%
>     maximum:  8.33%
> 
>   memory reclaimed per callback:
>     median:    3.80 MiB
>     p95:      30.45 MiB
>     maximum:  92.73 MiB
> 
> The longest callback took 271.36 ms. Its compactable ratio was 3.25%,
> and it released 7,650 pages, or about 29.88 MiB.
> 
> There was also a 241.91 ms callback (with 30 schedule-outs) with a
> compactable ratio of 0.44%. It released 1,019 pages, or about
> 3.98 MiB.
> 
> Based on this data, it seems better to remove the shrinker.
> 
> Would you prefer that I change v2 to remove the zsmalloc shrinker
> callbacks directly?

Let's bring in heavy artillery to this discussion, in addition to Andrew
and Minchan, adding Nhat, Yosry, Barry, Johannes, Brian (random order).

Folks, I'm bullish on removal of zsmalloc shrinker callbacks.
I don't think those buy us much apart from memcpy-s and lock
contention.  Systems that want to compact zsmalloc have a sysfs
knob (and API) to do so (based on zram mm_stat numbers).

Any thoughts?