FROMLIST: mm: add speculative page fault vmstats

Add speculative_pgfault vmstat counter to count successful speculative page
fault handling.

Also fixing a minor typo in include/linux/vm_event_item.h.

Change-Id: I0d3f3dc5195e1156d4b8edf83aff9d8d85904e8e
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Link: https://lore.kernel.org/lkml/1523975611-15978-24-git-send-email-ldufour@linux.vnet.ibm.com/
Bug: 161210518
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

include/linux/vm_event_item.h

@@ -120,6 +120,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_SWAP
 		SWAP_RA,
 		SWAP_RA_HIT,
+#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+		SPECULATIVE_PGFAULT,
 #endif
 		NR_VM_EVENT_ITEMS
 };

mm/memory.c

@@ -5014,6 +5014,7 @@ int __handle_speculative_fault(struct mm_struct *mm, unsigned long address,
 	 * If there is no need to retry, don't return the vma to the caller.
 	 */
 	if (ret != VM_FAULT_RETRY) {
+		count_vm_event(SPECULATIVE_PGFAULT);
 		put_vma(vmf.vma);
 		*vma = NULL;
 	}

mm/vmstat.c

@@ -1348,6 +1348,9 @@ const char * const vmstat_text[] = {
 	"swap_ra",
 	"swap_ra_hit",
 #endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+	"speculative_pgfault"
+#endif
 #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */