mm/vmalloc: query dynamic DEBUG_PAGEALLOC setting

As CONFIG_DEBUG_PAGEALLOC can be enabled/disabled via kernel parameters
we can optimize some cases by checking the enablement state.

This is follow-up work for Christian's Optimize CONFIG_DEBUG_PAGEALLOC:

  https://lkml.org/lkml/2016/1/27/194

Remaining work is to make sparc to be aware of this but it looks not
easy for me so I skip that in this series.

This patch (of 5):

We can disable debug_pagealloc processing even if the code is complied
with CONFIG_DEBUG_PAGEALLOC.  This patch changes the code to query
whether it is enabled or not in runtime.

[akpm@linux-foundation.org: update comment, per David.  Adjust comment to use 80 cols]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index fb42a5b..d4b2e34 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -531,22 +531,21 @@ static void unmap_vmap_area(struct vmap_area *va)
 static void vmap_debug_free_range(unsigned long start, unsigned long end)
 {
        /*
-        * Unmap page tables and force a TLB flush immediately if
-        * CONFIG_DEBUG_PAGEALLOC is set. This catches use after free
-        * bugs similarly to those in linear kernel virtual address
-        * space after a page has been freed.
+        * Unmap page tables and force a TLB flush immediately if pagealloc
+        * debugging is enabled.  This catches use after free bugs similarly to
+        * those in linear kernel virtual address space after a page has been
+        * freed.
         *
-        * All the lazy freeing logic is still retained, in order to
-        * minimise intrusiveness of this debugging feature.
+        * All the lazy freeing logic is still retained, in order to minimise
+        * intrusiveness of this debugging feature.
         *
-        * This is going to be *slow* (linear kernel virtual address
-        * debugging doesn't do a broadcast TLB flush so it is a lot
-        * faster).
+        * This is going to be *slow* (linear kernel virtual address debugging
+        * doesn't do a broadcast TLB flush so it is a lot faster).
         */
-#ifdef CONFIG_DEBUG_PAGEALLOC
-       vunmap_page_range(start, end);
-       flush_tlb_kernel_range(start, end);
-#endif
+       if (debug_pagealloc_enabled()) {
+               vunmap_page_range(start, end);
+               flush_tlb_kernel_range(start, end);
+       }
 }
 
 /*