[RFC PATCH v1 7/7] mm: For IAA batching, reduce SWAP_BATCH and modify swap slot cache thresholds.

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

When IAA is used for compress batching and decompress batching of folios,
we significantly reduce the swapout-swapin path latencies, such
that swap page-faults' latencies are reduced. This means swap entries will
need to be freed more often, and swap slots will have to be released more
often.

The existing SWAP_BATCH and SWAP_SLOTS_CACHE_SIZE value of 64
can cause lock contention of the swap_info_struct lock in
swapcache_free_entries and cpu hardlockups can result in highly contended
server scenarios.

To prevent this, the SWAP_BATCH and SWAP_SLOTS_CACHE_SIZE
has been reduced to 16 if IAA is used for compress/decompress batching. The
swap_slots_cache activate/deactive thresholds have been modified
accordingly, so that we don't compromise performance for stability.

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
 include/linux/swap.h       | 7 +++++++
 include/linux/swap_slots.h | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index ca533b478c21..3987faa0a2ff 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -13,6 +13,7 @@
 #include <linux/pagemap.h>
 #include <linux/atomic.h>
 #include <linux/page-flags.h>
+#include <linux/pagevec.h>
 #include <uapi/linux/mempolicy.h>
 #include <asm/page.h>
 
@@ -32,7 +33,13 @@ struct pagevec;
 #define SWAP_FLAGS_VALID	(SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \
 				 SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | \
 				 SWAP_FLAG_DISCARD_PAGES)
+
+#if defined(CONFIG_ZSWAP_STORE_BATCHING_ENABLED) || \
+	defined(CONFIG_ZSWAP_LOAD_BATCHING_ENABLED)
+#define SWAP_BATCH 16
+#else
 #define SWAP_BATCH 64
+#endif
 
 static inline int current_is_kswapd(void)
 {
diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h
index 15adfb8c813a..1b6e4e2798bd 100644
--- a/include/linux/swap_slots.h
+++ b/include/linux/swap_slots.h
@@ -7,8 +7,15 @@
 #include <linux/mutex.h>
 
 #define SWAP_SLOTS_CACHE_SIZE			SWAP_BATCH
+
+#if defined(CONFIG_ZSWAP_STORE_BATCHING_ENABLED) || \
+	defined(CONFIG_ZSWAP_LOAD_BATCHING_ENABLED)
+#define THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE	(40*SWAP_SLOTS_CACHE_SIZE)
+#define THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE	(16*SWAP_SLOTS_CACHE_SIZE)
+#else
 #define THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE	(5*SWAP_SLOTS_CACHE_SIZE)
 #define THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE	(2*SWAP_SLOTS_CACHE_SIZE)
+#endif
 
 struct swap_slots_cache {
 	bool		lock_initialized;
-- 
2.27.0