mm: increase folio batch size

On a 104 thread, 2 socket Skylake system, Intel report a 4.7% performance
reduction with will-it-scale page_fault2.  This was due to reducing the
size of the batch from 32 to 15.  Increasing the folio batch size from 15
to 31 gives a performance increase of 12.5% relative to the original, or
17.2% relative to the reduced performance commit.

The penalty of this commit is an additional 128 bytes of stack usage.  Six
folio_batches are also allocated from percpu memory in cpu_fbatches so
that will be an additional 768 bytes of percpu memory (per CPU).  Tim Chen
originally submitted a patch like this in 2020:
https://lore.kernel.org/linux-mm/d1cc9f12a8ad6c2a52cb600d93b06b064f2bbc57.1593205965.git.tim.c.chen@linux.intel.com/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 99fbb6b ("mm: make folios_put() the basis of release_pages()")
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Tested-by: Yujie Liu <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

include/linux/pagevec.h

@@ -11,8 +11,8 @@
 
 #include <linux/types.h>
 
-/* 15 pointers + header align the folio_batch structure to a power of two */
-#define PAGEVEC_SIZE	15
+/* 31 pointers + header align the folio_batch structure to a power of two */
+#define PAGEVEC_SIZE	31
 
 struct folio;