Linus:：我略微出手修改几行内核代码就提升了2.6%性能

@@ -38,6 +38,7 @@
 #else  #define can_do_masked_user_access() 0  #define masked_user_access_begin(src) NULL+ #define mask_user_address(src) (src) #endif
 /*@@ -159,19 +160,27 @@ _inline_copy_from_user(void *to, const void __user *from, unsigned long n) {   unsigned long res = n;   might_fault();-  if (!should_fail_usercopy() && likely(access_ok(from, n))) {+  if (should_fail_usercopy())+    goto fail;+  if (can_do_masked_user_access())+    from = mask_user_address(from);+  else {+    if (!access_ok(from, n))+      goto fail;     /*      * Ensure that bad access_ok() speculation will not      * lead to nasty side effects *after* the copy is      * finished:      */     barrier_nospec();-    instrument_copy_from_user_before(to, from, n);-    res = raw_copy_from_user(to, from, n);-    instrument_copy_from_user_after(to, from, n, res);   }-  if (unlikely(res))-    memset(to + (n - res), 0, res);+  instrument_copy_from_user_before(to, from, n);+  res = raw_copy_from_user(to, from, n);+  instrument_copy_from_user_after(to, from, n, res);+  if (likely(!res))+    return 0;+fail:+  memset(to + (n - res), 0, res);   return res; } extern __must_check unsigned long