[RFC PATCH v1 3/7] pagevec: struct folio_batch changes for decompress batching interface.

[Kanchana P Sridhar]

Made these changes to "struct folio_batch" for use in the
swapin_readahead() based zswap load batching interface for parallel
decompressions with IAA:

 1) Moved SWAP_RA_ORDER_CEILING definition to pagevec.h.
 2) Increased PAGEVEC_SIZE to (1UL << SWAP_RA_ORDER_CEILING),
    because vm.page-cluster=5 requires capacity for 32 folios.
 3) Made folio_batch_add() more fail-safe.

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
---
 include/linux/pagevec.h | 13 ++++++++++---
 mm/swap_state.c         |  2 --
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 5d3a0cccc6bf..c9bab240fb6e 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -11,8 +11,14 @@
 
 #include <linux/types.h>
 
-/* 31 pointers + header align the folio_batch structure to a power of two */
-#define PAGEVEC_SIZE	31
+/*
+ * For page-cluster of 5, I noticed that space for 31 pointers was
+ * insufficient. Increasing this to meet the requirements for folio_batch
+ * usage in the swap read decompress batching interface that is based on
+ * swapin_readahead().
+ */
+#define SWAP_RA_ORDER_CEILING	5
+#define PAGEVEC_SIZE	(1UL << SWAP_RA_ORDER_CEILING)
 
 struct folio;
 
@@ -74,7 +80,8 @@ static inline unsigned int folio_batch_space(struct folio_batch *fbatch)
 static inline unsigned folio_batch_add(struct folio_batch *fbatch,
 		struct folio *folio)
 {
-	fbatch->folios[fbatch->nr++] = folio;
+	if (folio_batch_space(fbatch) > 0)
+		fbatch->folios[fbatch->nr++] = folio;
 	return folio_batch_space(fbatch);
 }
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 3cebbff40804..0673593d363c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -44,8 +44,6 @@ struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
 static bool enable_vma_readahead __read_mostly = true;
 
-#define SWAP_RA_ORDER_CEILING	5
-
 #define SWAP_RA_WIN_SHIFT	(PAGE_SHIFT / 2)
 #define SWAP_RA_HITS_MASK	((1UL << SWAP_RA_WIN_SHIFT) - 1)
 #define SWAP_RA_HITS_MAX	SWAP_RA_HITS_MASK
-- 
2.27.0