The sysctl vm.compress-batching parameter is 0 by default. If the platform
has Intel IAA, the user can run experiments with IAA compress batching of
large folios in zswap_store() as follows:

sysctl vm.compress-batching=1
echo deflate-iaa > /sys/module/zswap/parameters/compressor

This is expected to significantly improve zswap_store() latency of swapping
out large folios due to parallel compression of 8 pages in the large folio
at a time, in hardware.

Setting vm.compress-batching to "1" takes effect only if the zswap
compression algorithm's crypto_acomp registers implementations for the
batch_compress() and batch_decompress() API. In other words, compress
batching works only with the iaa_crypto driver, that does register these
new batching API. It is a no-op for compressors that do not register the
batching API.

The sysctl vm.compress-batching acts as a switch because it takes effect
upon future zswap_store() calls on any given core. If the switch is "1",
large folios will use parallel batched compression of the folio's pages.
If the switch is "0", zswap_store() will use sequential compression for
storing every page in a large folio.

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
 include/linux/mm.h | 2 ++
 kernel/sysctl.c    | 9 +++++++++
 mm/swap.c          | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fecd47239fa9..f61915aa2f37 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -82,8 +82,10 @@ extern const int page_cluster_max;
 
 #ifdef CONFIG_SYSCTL
 extern int sysctl_legacy_va_layout;
+extern unsigned int compress_batching;
 #else
 #define sysctl_legacy_va_layout 0
+#define compress_batching 0
 #endif
 
 #ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 79e6cb1d5c48..e298857595b4 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2064,6 +2064,15 @@ static struct ctl_table vm_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= (void *)&page_cluster_max,
 	},
+	{
+		.procname	= "compress-batching",
+		.data		= &compress_batching,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_douintvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 	{
 		.procname	= "dirtytime_expire_seconds",
 		.data		= &dirtytime_expire_interval,
diff --git a/mm/swap.c b/mm/swap.c
index 638a3f001676..bc4c9079769e 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -47,6 +47,9 @@
 int page_cluster;
 const int page_cluster_max = 31;
 
+/* Enable/disable compress batching during swapout. */
+unsigned int compress_batching;
+
 struct cpu_fbatches {
 	/*
 	 * The following folio batches are grouped together because they are protected
@@ -1074,4 +1077,7 @@ void __init swap_setup(void)
 	 * Right now other parts of the system means that we
 	 * _really_ don't want to cluster much more
 	 */
+
+	/* Disable compress batching during swapout by default. */
+	compress_batching = 0;
 }
-- 
2.27.0

On Wed, Nov 06, 2024 at 11:21:04AM -0800, Kanchana P Sridhar wrote:
> The sysctl vm.compress-batching parameter is 0 by default. If the platform
> has Intel IAA, the user can run experiments with IAA compress batching of
> large folios in zswap_store() as follows:
> 
> sysctl vm.compress-batching=1
> echo deflate-iaa > /sys/module/zswap/parameters/compressor

A sysctl seems uncalled for. Can't the batching code be gated on
deflate-iaa being the compressor? It can still be generalized later if
another compressor is shown to benefit from batching.

On Thu, Nov 7, 2024 at 9:34 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Wed, Nov 06, 2024 at 11:21:04AM -0800, Kanchana P Sridhar wrote:
> > The sysctl vm.compress-batching parameter is 0 by default. If the platform
> > has Intel IAA, the user can run experiments with IAA compress batching of
> > large folios in zswap_store() as follows:
> >
> > sysctl vm.compress-batching=1
> > echo deflate-iaa > /sys/module/zswap/parameters/compressor
>
> A sysctl seems uncalled for. Can't the batching code be gated on
> deflate-iaa being the compressor? It can still be generalized later if
> another compressor is shown to benefit from batching.

+1

> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@google.com>
> Sent: Friday, November 8, 2024 12:24 PM
> To: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>; linux-
> kernel@vger.kernel.org; linux-mm@kvack.org; nphamcs@gmail.com;
> chengming.zhou@linux.dev; usamaarif642@gmail.com;
> ryan.roberts@arm.com; Huang, Ying <ying.huang@intel.com>;
> 21cnbao@gmail.com; akpm@linux-foundation.org; 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>; zanussi@kernel.org; Feghali, Wajdi K
> <wajdi.k.feghali@intel.com>; Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v3 12/13] mm: Add sysctl vm.compress-batching switch
> for compress batching during swapout.
> 
> On Thu, Nov 7, 2024 at 9:34 AM Johannes Weiner <hannes@cmpxchg.org>
> wrote:
> >
> > On Wed, Nov 06, 2024 at 11:21:04AM -0800, Kanchana P Sridhar wrote:
> > > The sysctl vm.compress-batching parameter is 0 by default. If the platform
> > > has Intel IAA, the user can run experiments with IAA compress batching of
> > > large folios in zswap_store() as follows:
> > >
> > > sysctl vm.compress-batching=1
> > > echo deflate-iaa > /sys/module/zswap/parameters/compressor
> >
> > A sysctl seems uncalled for. Can't the batching code be gated on
> > deflate-iaa being the compressor? It can still be generalized later if
> > another compressor is shown to benefit from batching.
> 
> +1

Thanks Yosry & Johannes. Will proceed as suggested.

Thanks,
Kanchana

> -----Original Message-----
> From: Johannes Weiner <hannes@cmpxchg.org>
> Sent: Thursday, November 7, 2024 9:34 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> yosryahmed@google.com; nphamcs@gmail.com;
> chengming.zhou@linux.dev; usamaarif642@gmail.com;
> ryan.roberts@arm.com; Huang, Ying <ying.huang@intel.com>;
> 21cnbao@gmail.com; akpm@linux-foundation.org; 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>; zanussi@kernel.org; Feghali, Wajdi K
> <wajdi.k.feghali@intel.com>; Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v3 12/13] mm: Add sysctl vm.compress-batching switch
> for compress batching during swapout.
> 
> On Wed, Nov 06, 2024 at 11:21:04AM -0800, Kanchana P Sridhar wrote:
> > The sysctl vm.compress-batching parameter is 0 by default. If the platform
> > has Intel IAA, the user can run experiments with IAA compress batching of
> > large folios in zswap_store() as follows:
> >
> > sysctl vm.compress-batching=1
> > echo deflate-iaa > /sys/module/zswap/parameters/compressor
> 
> A sysctl seems uncalled for. Can't the batching code be gated on
> deflate-iaa being the compressor? It can still be generalized later if
> another compressor is shown to benefit from batching.

That's a very valid point. I will gate the batching code based on the
availability of the crypto batch_compress() and batch_decompress()
interfaces in the compressor. I agree, this can still be generalized later to
other compressors, potentially via these same batching API.

Thanks,
Kanchana

On Wed,  6 Nov 2024 11:21:04 -0800 Kanchana P Sridhar <kanchana.p.sridhar@intel.com> wrote:

>  extern int sysctl_legacy_va_layout;
> +extern unsigned int compress_batching;

nit: I suggest calling this "sysctl_compress_batching".  See how we
treated sysctl_legacy_va_layout.

> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -47,6 +47,9 @@
>  int page_cluster;
>  const int page_cluster_max = 31;
>  
> +/* Enable/disable compress batching during swapout. */
> +unsigned int compress_batching;
> +
>  struct cpu_fbatches {
>  	/*
>  	 * The following folio batches are grouped together because they are protected
> @@ -1074,4 +1077,7 @@ void __init swap_setup(void)
>  	 * Right now other parts of the system means that we
>  	 * _really_ don't want to cluster much more
>  	 */
> +
> +	/* Disable compress batching during swapout by default. */
> +	compress_batching = 0;

Not really needed?  The compiler already did that.

>  }

Hi Andrew,

> -----Original Message-----
> From: Andrew Morton <akpm@linux-foundation.org>
> Sent: Wednesday, November 6, 2024 12:18 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; yosryahmed@google.com; nphamcs@gmail.com;
> chengming.zhou@linux.dev; usamaarif642@gmail.com;
> ryan.roberts@arm.com; Huang, Ying <ying.huang@intel.com>;
> 21cnbao@gmail.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>;
> zanussi@kernel.org; Feghali, Wajdi K <wajdi.k.feghali@intel.com>; Gopal,
> Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v3 12/13] mm: Add sysctl vm.compress-batching switch
> for compress batching during swapout.
> 
> On Wed,  6 Nov 2024 11:21:04 -0800 Kanchana P Sridhar
> <kanchana.p.sridhar@intel.com> wrote:
> 
> >  extern int sysctl_legacy_va_layout;
> > +extern unsigned int compress_batching;
> 
> nit: I suggest calling this "sysctl_compress_batching".  See how we
> treated sysctl_legacy_va_layout.

Thanks for the code review comments. Sure, I will incorporate this in v4.

> 
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -47,6 +47,9 @@
> >  int page_cluster;
> >  const int page_cluster_max = 31;
> >
> > +/* Enable/disable compress batching during swapout. */
> > +unsigned int compress_batching;
> > +
> >  struct cpu_fbatches {
> >  	/*
> >  	 * The following folio batches are grouped together because they are
> protected
> > @@ -1074,4 +1077,7 @@ void __init swap_setup(void)
> >  	 * Right now other parts of the system means that we
> >  	 * _really_ don't want to cluster much more
> >  	 */
> > +
> > +	/* Disable compress batching during swapout by default. */
> > +	compress_batching = 0;
> 
> Not really needed?  The compiler already did that.

Sure, will address this in v4.

Thanks,
Kanchana

> 
> >  }