linux-kernel - RE: [PATCH v11 23/24] mm: zswap: zswap_store() will process a large folio in batches.

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Message-ID: <PH7PR11MB81218BC3475BA5799E4FEA4DC93AA@PH7PR11MB8121.namprd11.prod.outlook.com>
Date: Fri, 29 Aug 2025 03:06:59 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Barry Song <21cnbao@...il.com>
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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	<wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>,
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v11 23/24] mm: zswap: zswap_store() will process a large
 folio in batches.


> -----Original Message-----
> From: Barry Song <21cnbao@...il.com>
> Sent: Thursday, August 28, 2025 5:00 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> hannes@...xchg.org; yosry.ahmed@...ux.dev; nphamcs@...il.com;
> chengming.zhou@...ux.dev; usamaarif642@...il.com;
> ryan.roberts@....com; ying.huang@...ux.alibaba.com; akpm@...ux-
> foundation.org; senozhatsky@...omium.org; 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 v11 23/24] mm: zswap: zswap_store() will process a
> large folio in batches.
> 
> On Fri, Aug 1, 2025 at 4:36 PM Kanchana P Sridhar
> <kanchana.p.sridhar@...el.com> wrote:
> >
> > This patch modifies zswap_store() to store a batch of pages in large
> > folios at a time, instead of storing one page at a time. It does this by
> > calling a new procedure zswap_store_pages() with a range of
> > "pool->batch_size" indices in the folio.
> >
> > zswap_store_pages() implements all the computes done earlier in
> > zswap_store_page() for a single-page, for multiple pages in a folio,
> > namely the "batch":
> >
> > 1) It starts by allocating all zswap entries required to store the
> >    batch. New procedures, zswap_entries_cache_alloc_batch() and
> >    zswap_entries_cache_free_batch() call kmem_cache_[free]alloc_bulk()
> >    to optimize the performance of this step.
> >
> > 2) Next, the entries fields are written, computes that need to be happen
> >    anyway, without modifying the zswap xarray/LRU publishing order. This
> >    improves latency by avoiding having the bring the entries into the
> >    cache for writing in different code blocks within this procedure.
> >
> > 3) Next, it calls zswap_compress() to sequentially compress each page in
> >    the batch.
> >
> > 4) Finally, it adds the batch's zswap entries to the xarray and LRU,
> >    charges zswap memory and increments zswap stats.
> >
> > 5) The error handling and cleanup required for all failure scenarios
> >    that can occur while storing a batch in zswap are consolidated to a
> >    single "store_pages_failed" label in zswap_store_pages(). Here again,
> >    we optimize performance by calling kmem_cache_free_bulk().
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
> > ---
> >  mm/zswap.c | 218 ++++++++++++++++++++++++++++++++++++-------------
> ----
> >  1 file changed, 149 insertions(+), 69 deletions(-)
> 
> This seems fine overall. However, could we pull some data from the
> cover letter. For example, even with hardware batching, we are still
> improving performance. Since your cover letter is very long, readers
> might fail to connect this data with the patches.

Sure, will add the data in the commit log.

Thanks,
Kanchana

> 
> Thanks
> Barry