[PATCH] x86-64: Increase TLB flush array size

The generic TLB flush functions kept upto 506 pages per
CPU to avoid too frequent IPIs.

This value was done for the L1 cache of older x86 CPUs,
but with modern CPUs it does not make much sense anymore.
TLB flushing is slow enough that using the L2 cache is fine.

This patch increases the flush array on x86-64 to cache
5350 pages. That is roughly 20MB with 4K pages. It speeds
up large munmaps in multithreaded processes on SMP considerably.

The cost is roughly 42k of memory per CPU, which is reasonable.

I only increased it on x86-64 for now, but it would probably
make sense to increase it everywhere. Embedded architectures
with SMP may keep it smaller to save some memory per CPU.

Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/asm-generic/tlb.h

···
  * and page free order so much..
  */
 #ifdef CONFIG_SMP
-  #define FREE_PTE_NR	506
+  #ifdef ARCH_FREE_PTR_NR
+    #define FREE_PTR_NR   ARCH_FREE_PTR_NR
+  #else
+    #define FREE_PTE_NR	506
+  #endif
   #define tlb_fast_mode(tlb) ((tlb)->nr == ~0U)
 #else
   #define FREE_PTE_NR	1

include/asm-x86_64/tlbflush.h

···
 #define TLBSTATE_OK	1
 #define TLBSTATE_LAZY	2
 
+/* Roughly an IPI every 20MB with 4k pages for freeing page table
+   ranges. Cost is about 42k of memory for each CPU. */
+#define ARCH_FREE_PTE_NR 5350	
+
 #endif
 
 #define flush_tlb_kernel_range(start, end) flush_tlb_all()