mm,vmacache: add debug data

Introduce a CONFIG_DEBUG_VM_VMACACHE option to enable counting the cache
hit rate -- exported in /proc/vmstat.

Any updates to the caching scheme needs this kind of data, thus it can
save some work re-implementing the counting all the time.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 34 insertions, 2 deletions

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 486c3972c0be..ced92345c963 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -80,6 +80,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                 NR_TLB_LOCAL_FLUSH_ALL,
                 NR_TLB_LOCAL_FLUSH_ONE,
 #endif /* CONFIG_DEBUG_TLBFLUSH */
+#ifdef CONFIG_DEBUG_VM_VMACACHE
+                VMACACHE_FIND_CALLS,
+                VMACACHE_FIND_HITS,
+#endif
                 NR_VM_EVENT_ITEMS
 };
 
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 45c9cd1daf7a..82e7db7f7100 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -95,6 +95,12 @@ static inline void vm_events_fold_cpu(int cpu)
 #define count_vm_tlb_events(x, y) do { (void)(y); } while (0)
 #endif
 
+#ifdef CONFIG_DEBUG_VM_VMACACHE
+#define count_vm_vmacache_event(x) count_vm_event(x)
+#else
+#define count_vm_vmacache_event(x) do {} while (0)
+#endif
+
 #define __count_zone_vm_events(item, zone, delta) \
                 __count_vm_events(item##_NORMAL - ZONE_NORMAL + \
                 zone_idx(zone), delta)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 99c8bfee1b00..c2de65045a40 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -501,6 +501,16 @@ config DEBUG_VM
 
           If unsure, say N.
 
+config DEBUG_VM_VMACACHE
+        bool "Debug VMA caching"
+        depends on DEBUG_VM
+        help
+          Enable this to turn on VMA caching debug information. Doing so
+          can cause significant overhead, so only enable it in non-production
+          environments.
+
+          If unsure, say N.
+
 config DEBUG_VM_RB
         bool "Debug VM red-black trees"
         depends on DEBUG_VM
diff --git a/mm/vmacache.c b/mm/vmacache.c
index 1037a3bab505..658ed3b3e38d 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -78,6 +78,8 @@ struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
         if (!vmacache_valid(mm))
                 return NULL;
 
+        count_vm_vmacache_event(VMACACHE_FIND_CALLS);
+
         for (i = 0; i < VMACACHE_SIZE; i++) {
                 struct vm_area_struct *vma = current->vmacache[i];
 
@@ -85,8 +87,10 @@ struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
                         continue;
                 if (WARN_ON_ONCE(vma->vm_mm != mm))
                         break;
-                if (vma->vm_start <= addr && vma->vm_end > addr)
+                if (vma->vm_start <= addr && vma->vm_end > addr) {
+                        count_vm_vmacache_event(VMACACHE_FIND_HITS);
                         return vma;
+                }
         }
 
         return NULL;
@@ -102,11 +106,15 @@ struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
         if (!vmacache_valid(mm))
                 return NULL;
 
+        count_vm_vmacache_event(VMACACHE_FIND_CALLS);
+
         for (i = 0; i < VMACACHE_SIZE; i++) {
                 struct vm_area_struct *vma = current->vmacache[i];
 
-                if (vma && vma->vm_start == start && vma->vm_end == end)
+                if (vma && vma->vm_start == start && vma->vm_end == end) {
+                        count_vm_vmacache_event(VMACACHE_FIND_HITS);
                         return vma;
+                }
         }
 
         return NULL;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 302dd076b8bf..82ce17ce58c4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -866,6 +866,10 @@ const char * const vmstat_text[] = {
         "nr_tlb_local_flush_one",
 #endif /* CONFIG_DEBUG_TLBFLUSH */
 
+#ifdef CONFIG_DEBUG_VM_VMACACHE
+        "vmacache_find_calls",
+        "vmacache_find_hits",
+#endif
 #endif /* CONFIG_VM_EVENTS_COUNTERS */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */