Message-ID: <SJ2PR11MB847267511A5B6CF9EBFA1A0DC9A9A@SJ2PR11MB8472.namprd11.prod.outlook.com>
Date: Fri, 19 Dec 2025 02:29:15 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
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Subject: RE: [PATCH v13 22/22] mm: zswap: Batched zswap_compress() with
 compress batching of large folios.


> -----Original Message-----
> From: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Sent: Thursday, November 13, 2025 4:46 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> hannes@...xchg.org; nphamcs@...il.com; chengming.zhou@...ux.dev;
> usamaarif642@...il.com; ryan.roberts@....com; 21cnbao@...il.com;
> ying.huang@...ux.alibaba.com; akpm@...ux-foundation.org;
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> davem@...emloft.net; clabbe@...libre.com; ardb@...nel.org;
> ebiggers@...gle.com; surenb@...gle.com; Accardi, Kristen C
> <kristen.c.accardi@...el.com>; Gomes, Vinicius <vinicius.gomes@...el.com>;
> Feghali, Wajdi K <wajdi.k.feghali@...el.com>; Gopal, Vinodh
> <vinodh.gopal@...el.com>
> Subject: Re: [PATCH v13 22/22] mm: zswap: Batched zswap_compress() with
> compress batching of large folios.
[...]
> > > > Architectural considerations for the zswap batching framework:
> > > >
> > >
> ==============================================================
> > > > We have designed the zswap batching framework to be
> > > > hardware-agnostic. It has no dependencies on Intel-specific features
> and
> > > > can be leveraged by any hardware accelerator or software-based
> > > > compressor. In other words, the framework is open and inclusive by
> > > > design.
> > > >
> > > > Other ongoing work that can use batching:
> > > > =========================================
> > > > This patch-series demonstrates the performance benefits of compress
> > > > batching when used in zswap_store() of large folios. shrink_folio_list()
> > > > "reclaim batching" of any-order folios is the major next work that uses
> > > > the zswap compress batching framework: our testing of
> kernel_compilation
> > > > with writeback and the zswap shrinker indicates 10X fewer pages get
> > > > written back when we reclaim 32 folios as a batch, as compared to one
> > > > folio at a time: this is with deflate-iaa and with zstd. We expect to
> > > > submit a patch-series with this data and the resulting performance
> > > > improvements shortly. Reclaim batching relieves memory pressure
> faster
> > > > than reclaiming one folio at a time, hence alleviates the need to scan
> > > > slab memory for writeback.
> > > >
> > > > Nhat has given ideas on using batching with the ongoing kcompressd
> work,
> > > > as well as beneficially using decompression batching & block IO batching
> > > > to improve zswap writeback efficiency.
> > > >
> > > > Experiments that combine zswap compress batching, reclaim batching,
> > > > swapin_readahead() decompression batching of prefetched pages, and
> > > > writeback batching show that 0 pages are written back with deflate-iaa
> > > > and zstd. For comparison, the baselines for these compressors see
> > > > 200K-800K pages written to disk (kernel compilation 'allmod' config).
> > > >
> > > > To summarize, these are future clients of the batching framework:
> > > >
> > > >    - shrink_folio_list() reclaim batching of multiple folios:
> > > >        Implemented, will submit patch-series.
> > > >    - zswap writeback with decompress batching:
> > > >        Implemented, will submit patch-series.
> > > >    - zram:
> > > >        Implemented, will submit patch-series.
> > > >    - kcompressd:
> > > >        Not yet implemented.
> > > >    - file systems:
> > > >        Not yet implemented.
> > > >    - swapin_readahead() decompression batching of prefetched pages:
> > > >        Implemented, will submit patch-series.
> > > >
> > > > Additionally, any place we have folios that need to be compressed, can
> > > > potentially be parallelized.

[...]

> For example, you should remove mentions of ongoing work and future work,
> simply because things change and they may not land. Just briefly
> mentioning that there are future use cases (with maybe an example) is
> sufficient.

Hi Yosry,

The mentions of ongoing/future work were included as per Andrew's suggestion.
Hence, I would like to keep these in the commit log. Hope this is Ok with you?

Thanks,
Kanchana

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