Re: [PATCH v1 0/8] Batched zswap_store() with compression batching

[Yosry Ahmed]

On Thu, Oct 15, 2026 at 3:00 PM Kanchana P. Sridhar
<kanchanapsridhar2026@xxxxxxxxx> wrote:
>
> On Wed, Oct 14, 2026 at 8:45 AM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> >
> > On Thu, Oct 08, 2026 at 11:28:06AM -0700, Kanchana P. Sridhar wrote:
> > > v1: Batched zswap_store() with compression batching
> > > ===================================================
> > >
> > > This series is a spin-off of "v14: zswap compression batching with optimized
> > > iaa_crypto driver" [1], and focuses on the generic crypto_acomp and zswap
> > > compression batching enablers. Resuming work on this series following a gap
> > > since v14 (January 2026). Please note that my email address and affiliation have
> > > changed from kanchana.p.sridhar@xxxxxxxxx to kanchanapsridhar2026@xxxxxxxxx. I
> > > have retained the original Intel sign-offs on prior patches for historical
> > > attribution while signing off v1 of this series with my current address.
> > >
> > > To summarize the main contribution of this patch series: Batching is introduced
> > > in zswap_store() of large folios: we carve out a large folio into batches of
> > > ZSWAP_MAX_BATCH_SIZE (8 pages) for software compressors, and store each
> > > batch. Moving the fundamental operations that need to be happen to store a page
> > > to now work at the granularity of a batch offers opportunities to optimize them
> > > from these perspectives:
> > >
> > > 1) Utilize existing kernel API that minimize obtaining locks for bulk
> > >    operations, e.g. kmem_cache_alloc_bulk()/kmem_cache_free_bulk().
> > >
> > > 2) We keep the working set for each of the core store functionalities (alloc
> > >    entries, compress pages, store pages in zsmalloc) to be focused on a
> > >    batch, thereby minimizing cache evictions and benefiting from cache
> > >    locality.
> > >
> > > 3) Along the lines of (1), the main zswap_compress() batching routine obtains
> > >    the acomp_ctx mutex lock once per batch, and releases it after it has
> > >    processed all pages in that batch.
> > >
> > > 4) Any zswap store functionality that works on a batch can potentially be
> > >    parallelized as a next step, to further improve performance.
> > >
> > > Performance data: usemem with 60% over-commit:
> > > ==============================================
> >
> > How much of the performance benefits come from patch 6 vs patch 8?
>
> This is how the performance changes: Average throughput is averaged
> from 10 iterations of usemem.
>
> patch 6: 19,119 KB/s
> patch 8: 17,593 KB/s
>
> So the acomp_do_req_chain() path that ZSTD goes through with patch 8
> causes a regression, even though it provides a generic batching
> framework in acomp.
>
> I was able to retrieve performance with the following change in acompress.c:

Why add it to begin with in this case?

>
> patch 3 with this change in acompress.c: 19,578 KB/s
>
> diff --git a/crypto/acompress.c b/crypto/acompress.c
> index 192ea996e779..dc609bd7d927 100644
> --- a/crypto/acompress.c
> +++ b/crypto/acompress.c
> @@ -293,8 +293,12 @@ int crypto_acomp_compress(struct acomp_req *req)
>                 return -EAGAIN;
>
>         if (likely(req->unit_size && acomp_request_issg(req))) {
> -               if (!crypto_acomp_req_seg(tfm))
> -                       return acomp_do_req_chain(req, true);
> +               if (!crypto_acomp_req_seg(tfm)) {
> +                       int err = tfm->compress(req);
> +
> +                       req->dst->length = unlikely(err) ? err : req->dlen;
> +                       return err;
> +               }
>
>                 return tfm->compress(req);
>         }
>
> Herbert, would you be Ok with this change in patch 3?