[IA64] Avoid unnecessary TLB flushes when allocating memory

Improve performance of memory allocations on ia64 by avoiding a global TLB
purge to purge a single page from the file cache. This happens whenever we
evict a page from the buffer cache to make room for some other allocation.

Test case: Run 'find /usr -type f | xargs cat > /dev/null' in the
background to fill the buffer cache, then run something that uses memory,
e.g. 'gmake -j50 install'. Instrumentation showed that the number of
global TLB purges went from a few millions down to about 170 over a 12
hours run of the above.

The performance impact is particularly noticeable under virtualization,
because a virtual TLB is generally both larger and slower to purge than
a physical one.

Signed-off-by: Christophe de Dinechin <ddd@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/ia64/mm/tlb.c b/arch/ia64/mm/tlb.c
index cef164729db7..655da240d13c 100644
--- a/arch/ia64/mm/tlb.c
+++ b/arch/ia64/mm/tlb.c
@@ -10,6 +10,7 @@
  *              IPI based ptc implementation and A-step IPI implementation.
  * Rohit Seth <rohit.seth@intel.com>
  * Ken Chen <kenneth.w.chen@intel.com>
+ * Christophe de Dinechin <ddd@hp.com>: Avoid ptc.e on memory allocation
  */
 #include <linux/module.h>
 #include <linux/init.h>
@@ -89,9 +90,16 @@ ia64_global_tlb_purge (struct mm_struct *mm, unsigned long start,
 {
         static DEFINE_SPINLOCK(ptcg_lock);
 
-        if (mm != current->active_mm || !current->mm) {
-                flush_tlb_all();
-                return;
+        struct mm_struct *active_mm = current->active_mm;
+
+        if (mm != active_mm) {
+                /* Restore region IDs for mm */
+                if (mm && active_mm) {
+                        activate_context(mm);
+                } else {
+                        flush_tlb_all();
+                        return;
+                }
         }
 
         /* HW requires global serialization of ptc.ga.  */
@@ -107,6 +115,10 @@ ia64_global_tlb_purge (struct mm_struct *mm, unsigned long start,
                 } while (start < end);
         }
         spin_unlock(&ptcg_lock);
+
+        if (mm != active_mm) {
+                activate_context(active_mm);
+        }
 }
 
 void