Re: [PATCH 03/14] mm: Share the anon_vma ref counts between KSM and page migration

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On 04/06/2010 08:05 PM, Andrew Morton wrote:
On Fri,  2 Apr 2010 17:02:37 +0100
Mel Gorman<mel@xxxxxxxxx>  wrote:

+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+
+	/*
+	 * The external_refcount is taken by either KSM or page migration
+	 * to take a reference to an anon_vma when there is no
+	 * guarantee that the vma of page tables will exist for
+	 * the duration of the operation. A caller that takes
+	 * the reference is responsible for clearing up the
+	 * anon_vma if they are the last user on release
+	 */
+	atomic_t external_refcount;
  #endif

hah.

+	anonvma_external_refcount_init(anon_vma);

What a mouthful.  Can we do s/external_//g?

For the function, sure.

However, I believe it would be good to keep the variable
inside the anon_vma as "external_refcount", because the
VMAs attached to the anon_vma take a reference by being
on the list (and leave the refcount alone).

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