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.

[[email protected]: update comment, per David.  Adjust comment to use 80 cols]
Signed-off-by: Joonsoo Kim <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Takashi Iwai <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 12 insertions, 13 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index fb42a5bffe47..d4b2e34adae0 100644
--- 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);
+	}
 }
 
 /*