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Message-ID: <PH7PR11MB8121A8735058103B02EBCDBDC9EAA@PH7PR11MB8121.namprd11.prod.outlook.com>
Date: Mon, 13 Oct 2025 17:58:11 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
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"Gomes, Vinicius" <vinicius.gomes@...el.com>, "Feghali, Wajdi K"
<wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>,
"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v12 22/23] mm: zswap: zswap_store() will process a large
folio in batches.
> -----Original Message-----
> From: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Sent: Wednesday, October 1, 2025 2:21 PM
> To: Yosry Ahmed <yosry.ahmed@...ux.dev>
> 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;
> senozhatsky@...omium.org; sj@...nel.org; kasong@...cent.com; linux-
> crypto@...r.kernel.org; herbert@...dor.apana.org.au;
> 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>; Sridhar, Kanchana P
> <kanchana.p.sridhar@...el.com>
> Subject: RE: [PATCH v12 22/23] mm: zswap: zswap_store() will process a
> large folio in batches.
>
>
> > -----Original Message-----
> > From: Yosry Ahmed <yosry.ahmed@...ux.dev>
> > Sent: Wednesday, October 1, 2025 9:19 AM
> > 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;
> > senozhatsky@...omium.org; sj@...nel.org; kasong@...cent.com; linux-
> > crypto@...r.kernel.org; herbert@...dor.apana.org.au;
> > 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 v12 22/23] mm: zswap: zswap_store() will process a
> > large folio in batches.
> >
> > On Thu, Sep 25, 2025 at 08:35:01PM -0700, Kanchana P Sridhar wrote:
[...]
> > > @@ -158,6 +161,8 @@ struct zswap_pool {
> > > struct work_struct release_work;
> > > struct hlist_node node;
> > > char tfm_name[CRYPTO_MAX_ALG_NAME];
> > > + u8 compr_batch_size;
> > > + u8 store_batch_size;
> >
> > I don't think we need to store store_batch_size, seems trivial to
> > calculate at store time (perhaps in a helper).
> >
> > Taking a step back, is there any benefit to limiting store_batch_size to
> > compr_batch_size? Is there a disadvantage to using
> > ZSWAP_MAX_BATCH_SIZE
> > even if it's higher than the HW compression batch size?
>
> Thanks Yosry, for the code review comments. I had a discussion with
> Barry earlier on these very same topics as follow up to his review comments
> for v11, starting with [1]. Can you please go through the rationale for
> these design choices, and let me know if you have any questions:
>
> [1]: https://patchwork.kernel.org/comment/26530319/
>
[...]
> >
> > Does it actually matter if we do the initializations here vs. right
> > before inserting to the LRU (current behavior)?
>
> Yes, it impacts batching performance with software quite a bit.
[...]
> > Seems like if xa_store() fails we do not cleanup previously charged
> > objects, pool references, zswap_stored_pages, etc. Instead of rolling
> > all this back on failure, can we do all the xarray stores first and only
> > do the rest when we're at a point where no failure can happen? Would
> > that cause a performance regression?
>
> It would make the code more complicated and thus cause a performance
> regression. I have tried to balance code simplicity (which impacts
> performance)
> with correctness here. The "store_failed_idx" ensures that all partial work
> done
> in zswap_store_pages() for this batch, is cleaned up.
>
> The rest is handled in zswap_store() when it sees an error returned by
> zswap_store_pages().
>
Hi Yosry,
I was wondering if my explanations to the above comments answer
your questions? Please let me know.
The bulk entries alloc/free comments' follow-up is covered in the other
email.
Thanks,
Kanchana
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