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>

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 486c397..ced9234 100644 (file)
--- 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 45c9cd1..82e7db7 100644 (file)
--- 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 99c8bfe..c2de650 100644 (file)
--- 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 1037a3b..658ed3b 100644 (file)
--- 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 302dd07..82ce17c 100644 (file)
--- 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 */