[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 <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

arch/ia64/mm/tlb.c

···
  *              IPI based ptc implementation and A-step IPI implementation.
  * Rohit Seth <[e-mail]>
  * Ken Chen <[e-mail]>
+ * Christophe de Dinechin <[e-mail]>: Avoid ptc.e on memory allocation
  */
 #include <linux/module.h>
 #include <linux/init.h>
···
 {
 	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.  */
···
 		} while (start < end);
 	}
 	spin_unlock(&ptcg_lock);
+
+        if (mm != active_mm) {
+                activate_context(active_mm);
+        }
 }
 
 void