uml: speed up exec

flush_thread doesn't need to do a full page table walk in order to clear the
address space.  It knows what the end result needs to be, so it can call unmap
directly.

This results in a 10-20% speedup in an exec from bash.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/arch/um/kernel/skas/exec.c b/arch/um/kernel/skas/exec.c
index 54b795951372..580eb6468949 100644
--- a/arch/um/kernel/skas/exec.c
+++ b/arch/um/kernel/skas/exec.c
@@ -17,7 +17,17 @@
 
 void flush_thread_skas(void)
 {
-        force_flush_all();
+        void *data = NULL;
+        unsigned long end = proc_mm ? task_size : CONFIG_STUB_START;
+        int ret;
+
+        ret = unmap(&current->mm->context.skas.id, 0, end, 1, &data);
+        if(ret){
+                printk("flush_thread_skas - clearing address space failed, "
+                       "err = %d\n", ret);
+                force_sig(SIGKILL, current);
+        }
+
         switch_mm_skas(&current->mm->context.skas.id);
 }