RE: [PATCH v14 26/26] mm: zswap: Batched zswap_compress() for compress batching of large folios.

["Sridhar, Kanchana P" <kanchana.p.sridhar@intel.com>]

> -----Original Message-----
> From: Nhat Pham <nphamcs@gmail.com>
> Sent: Saturday, January 31, 2026 4:49 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; yosry.ahmed@linux.dev; chengming.zhou@linux.dev;
> usamaarif642@gmail.com; ryan.roberts@arm.com; 21cnbao@gmail.com;
> ying.huang@linux.alibaba.com; akpm@linux-foundation.org;
> senozhatsky@chromium.org; sj@kernel.org; kasong@tencent.com; linux-
> crypto@vger.kernel.org; herbert@gondor.apana.org.au;
> davem@davemloft.net; clabbe@baylibre.com; ardb@kernel.org;
> ebiggers@google.com; surenb@google.com; Accardi, Kristen C
> <kristen.c.accardi@intel.com>; Gomes, Vinicius <vinicius.gomes@intel.com>;
> Cabiddu, Giovanni <giovanni.cabiddu@intel.com>; Feghali, Wajdi K
> <wajdi.k.feghali@intel.com>
> Subject: Re: [PATCH v14 26/26] mm: zswap: Batched zswap_compress() for
> compress batching of large folios.
> 
> On Sat, Jan 31, 2026 at 12:32 PM Sridhar, Kanchana P
> <kanchana.p.sridhar@intel.com> wrote:
> >
> >
> > > -----Original Message-----
> > > From: Nhat Pham <nphamcs@gmail.com>
> > > Sent: Friday, January 30, 2026 5:13 PM
> > > To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> > > Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> > > hannes@cmpxchg.org; yosry.ahmed@linux.dev;
> chengming.zhou@linux.dev;
> > > usamaarif642@gmail.com; ryan.roberts@arm.com; 21cnbao@gmail.com;
> > > ying.huang@linux.alibaba.com; akpm@linux-foundation.org;
> > > senozhatsky@chromium.org; sj@kernel.org; kasong@tencent.com; linux-
> > > crypto@vger.kernel.org; herbert@gondor.apana.org.au;
> > > davem@davemloft.net; clabbe@baylibre.com; ardb@kernel.org;
> > > ebiggers@google.com; surenb@google.com; Accardi, Kristen C
> > > <kristen.c.accardi@intel.com>; Gomes, Vinicius
> <vinicius.gomes@intel.com>;
> > > Cabiddu, Giovanni <giovanni.cabiddu@intel.com>; Feghali, Wajdi K
> > > <wajdi.k.feghali@intel.com>
> > > Subject: Re: [PATCH v14 26/26] mm: zswap: Batched zswap_compress()
> for
> > > compress batching of large folios.
> > >
> > > On Sat, Jan 24, 2026 at 7:36 PM Kanchana P Sridhar
> > > <kanchana.p.sridhar@intel.com> wrote:
> > > >
> > > > We introduce a new batching implementation of zswap_compress() for
> > > > compressors that do and do not support batching. This eliminates code
> > > > duplication and facilitates code maintainability with the introduction
> > > > of compress batching.
> > > >
> > > > The vectorized implementation of calling the earlier zswap_compress()
> > > > sequentially, one page at a time in zswap_store_pages(), is replaced
> > > > with this new version of zswap_compress() that accepts multiple pages
> to
> > > > compress as a batch.
> > > >
> > > > If the compressor does not support batching, each page in the batch is
> > > > compressed and stored sequentially. If the compressor supports
> batching,
> > > > for e.g., 'deflate-iaa', the Intel IAA hardware accelerator, the batch
> > > > is compressed in parallel in hardware.
> > > >
> > > > If the batch is compressed without errors, the compressed buffers for
> > > > the batch are stored in zsmalloc. In case of compression errors, the
> > > > current behavior based on whether the folio is enabled for zswap
> > > > writeback, is preserved.
> > > >
> > > > The batched zswap_compress() incorporates Herbert's suggestion for
> > > > SG lists to represent the batch's inputs/outputs to interface with the
> > > > crypto API [1].
> > > >
> > > > Performance data:
> > > > =================
> > > > As suggested by Barry, this is the performance data gathered on Intel
> > > > Sapphire Rapids with two workloads:
> > > >
> > > > 1) 30 usemem processes in a 150 GB memory limited cgroup, each
> > > >    allocates 10G, i.e, effectively running at 50% memory pressure.
> > > > 2) kernel_compilation "defconfig", 32 threads, cgroup memory limit set
> > > >    to 1.7 GiB (50% memory pressure, since baseline memory usage is 3.4
> > > >    GiB): data averaged across 10 runs.
> > > >
> > > > To keep comparisons simple, all testing was done without the
> > > > zswap shrinker.
> > > >
> > > >
> > >
> ==============================================================
> > > ===========
> > > >   IAA                 mm-unstable-1-23-2026             v14
> > > >
> > >
> ==============================================================
> > > ===========
> > > >     zswap compressor            deflate-iaa     deflate-iaa   IAA Batching
> > > >                                                                   vs.
> > > >                                                             IAA Sequential
> > > >
> > >
> ==============================================================
> > > ===========
> > > >  usemem30, 64K folios:
> > > >
> > > >     Total throughput (KB/s)       6,226,967      10,551,714       69%
> > > >     Average throughput (KB/s)       207,565         351,723       69%
> > > >     elapsed time (sec)                99.19           67.45      -32%
> > > >     sys time (sec)                 2,356.19        1,580.47      -33%
> > > >
> > > >  usemem30, PMD folios:
> > > >
> > > >     Total throughput (KB/s)       6,347,201      11,315,500       78%
> > > >     Average throughput (KB/s)       211,573         377,183       78%
> > > >     elapsed time (sec)                88.14           63.37      -28%
> > > >     sys time (sec)                 2,025.53        1,455.23      -28%
> > > >
> > > >  kernel_compilation, 64K folios:
> > > >
> > > >     elapsed time (sec)               100.10           98.74     -1.4%
> > > >     sys time (sec)                   308.72          301.23       -2%
> > > >
> > > >  kernel_compilation, PMD folios:
> > > >
> > > >     elapsed time (sec)                95.29           93.44     -1.9%
> > > >     sys time (sec)                   346.21          344.48     -0.5%
> > > >
> > >
> ==============================================================
> > > ===========
> > > >
> > > >
> > >
> ==============================================================
> > > ===========
> > > >   ZSTD                mm-unstable-1-23-2026             v14
> > > >
> > >
> ==============================================================
> > > ===========
> > > >     zswap compressor                   zstd            zstd     v14 ZSTD
> > > >                                                              Improvement
> > > >
> > >
> ==============================================================
> > > ===========
> > > >  usemem30, 64K folios:
> > > >
> > > >     Total throughput (KB/s)       6,032,326       6,047,448      0.3%
> > > >     Average throughput (KB/s)       201,077         201,581      0.3%
> > > >     elapsed time (sec)                97.52           95.33     -2.2%
> > > >     sys time (sec)                 2,415.40        2,328.38       -4%
> > > >
> > > >  usemem30, PMD folios:
> > > >
> > > >     Total throughput (KB/s)       6,570,404       6,623,962      0.8%
> > > >     Average throughput (KB/s)       219,013         220,798      0.8%
> > > >     elapsed time (sec)                89.17           88.25       -1%
> > > >     sys time (sec)                 2,126.69        2,043.08       -4%
> > > >
> > > >  kernel_compilation, 64K folios:
> > > >
> > > >     elapsed time (sec)               100.89           99.98     -0.9%
> > > >     sys time (sec)                   417.49          414.62     -0.7%
> > > >
> > > >  kernel_compilation, PMD folios:
> > > >
> > > >     elapsed time (sec)                98.26           97.38     -0.9%
> > > >     sys time (sec)                   487.14          473.16     -2.9%
> > > >
> > >
> ==============================================================
> > > ===========
> > >
> > > The rest of the patch changelog (architectural and future
> > > considerations)  can stay in the cover letter. Let's not duplicate
> > > information :)
> > >
> > > Keep the patch changelog limited to only the changes in the patch
> > > itself (unless we need some clarifications imminently relevant).
> >
> > Hi Nhat,
> >
> > Thanks for this comment. Yosry had also pointed this out in [1]. I have
> > been including the architectural and future considerations in this change log
> > since Andrew had asked me to do so. I hope this is Ok?
> 
> Ah hmmmmm. For some reasons I was under the assumption that usually
> Andrew would concatenate the patch cover letter and the patch
> changelog before merging. Oh well.
> 
> If Andrew prefers including that here then I'm fine with it.

Ok, thank you Nhat!

Best regards,
Kanchana

> 
> >
> > [1]: https://patchwork.kernel.org/comment/26706240/
> >
> > >
> > > I'll review the remainder of the patch later :)
> >
> > Sure.
> >
> > Thanks,
> > Kanchana