[RFC PATCH v1 09/13] mm: zswap: Config variable to enable compress batching in zswap_store().

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

Add a new zswap config variable that controls whether zswap_store() will
compress a batch of pages, for instance, the pages in a large folio:

  CONFIG_ZSWAP_STORE_BATCHING_ENABLED

The existing CONFIG_CRYPTO_DEV_IAA_CRYPTO variable added in commit
ea7a5cbb4369 ("crypto: iaa - Add Intel IAA Compression Accelerator crypto
driver core") is used to detect if the system has the Intel Analytics
Accelerator (IAA), and the iaa_crypto module is available. If so, the
kernel build will prompt for CONFIG_ZSWAP_STORE_BATCHING_ENABLED. Hence,
users have the ability to set CONFIG_ZSWAP_STORE_BATCHING_ENABLED="y" only
on systems that have Intel IAA.

If CONFIG_ZSWAP_STORE_BATCHING_ENABLED is enabled, and IAA is configured
as the zswap compressor, zswap_store() will process the pages in a large
folio in batches, i.e., multiple pages at a time. Pages in a batch will be
compressed in parallel in hardware, then stored. On systems without Intel
IAA and/or if zswap uses software compressors, pages in the batch will be
compressed sequentially and stored.

The patch also implements a zswap API that returns the status of this
config variable.

Suggested-by: Ying Huang <ying.huang@intel.com>
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
 include/linux/zswap.h |  6 ++++++
 mm/Kconfig            | 12 ++++++++++++
 mm/zswap.c            | 14 ++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index d961ead91bf1..74ad2a24b309 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -24,6 +24,7 @@ struct zswap_lruvec_state {
 	atomic_long_t nr_disk_swapins;
 };
 
+bool zswap_store_batching_enabled(void);
 unsigned long zswap_total_pages(void);
 bool zswap_store(struct folio *folio);
 bool zswap_load(struct folio *folio);
@@ -39,6 +40,11 @@ bool zswap_never_enabled(void);
 
 struct zswap_lruvec_state {};
 
+static inline bool zswap_store_batching_enabled(void)
+{
+	return false;
+}
+
 static inline bool zswap_store(struct folio *folio)
 {
 	return false;
diff --git a/mm/Kconfig b/mm/Kconfig
index 33fa51d608dc..26d1a5cee471 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -125,6 +125,18 @@ config ZSWAP_COMPRESSOR_DEFAULT
        default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD
        default ""
 
+config ZSWAP_STORE_BATCHING_ENABLED
+	bool "Batching of zswap stores with Intel IAA"
+	depends on ZSWAP && CRYPTO_DEV_IAA_CRYPTO
+	default n
+	help
+	Enables zswap_store to swapout large folios in batches of 8 pages,
+	rather than a page at a time, if the system has Intel IAA for hardware
+	acceleration of compressions. If IAA is configured as the zswap
+	compressor, this will parallelize batch compression of upto 8 pages
+	in the folio in	hardware, thereby improving large folio compression
+	throughput and reducing swapout latency.
+
 choice
 	prompt "Default allocator"
 	depends on ZSWAP
diff --git a/mm/zswap.c b/mm/zswap.c
index 948c9745ee57..4893302d8c34 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -127,6 +127,15 @@ static bool zswap_shrinker_enabled = IS_ENABLED(
 		CONFIG_ZSWAP_SHRINKER_DEFAULT_ON);
 module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);
 
+/*
+ * Enable/disable batching of compressions if zswap_store is called with a
+ * large folio. If enabled, and if IAA is the zswap compressor, pages are
+ * compressed in parallel in batches of say, 8 pages.
+ * If not, every page is compressed sequentially.
+ */
+static bool __zswap_store_batching_enabled = IS_ENABLED(
+	CONFIG_ZSWAP_STORE_BATCHING_ENABLED);
+
 bool zswap_is_enabled(void)
 {
 	return zswap_enabled;
@@ -241,6 +250,11 @@ static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
 	pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,		\
 		 zpool_get_type((p)->zpool))
 
+__always_inline bool zswap_store_batching_enabled(void)
+{
+	return __zswap_store_batching_enabled;
+}
+
 /*********************************
 * pool functions
 **********************************/
-- 
2.27.0