This patch changes the anon_vma refcount to be 0 when the object is
free. It does this by adding 1 ref to being in use in the anon_vma
structure (iow. the anon_vma->head list is not empty).
This allows a simpler release scheme without having to check both the
refcount and the list as well as avoids taking a ref for each entry
on the list.
We then use this new refcount in the migration code to avoid a long
RCU read side section and convert page_lock_anon_vma() over to use
refcounts.
This later is done for each of convertion of anon_vma from spinlock
to mutex.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/rmap.h | 7 +++++++
mm/ksm.c | 9 +--------
mm/migrate.c | 17 ++++++-----------
mm/rmap.c | 43 +++++++++++++++++++++++++++++--------------
4 files changed, 43 insertions(+), 33 deletions(-)
Index: linux-2.6/include/linux/rmap.h
===================================================================
--- linux-2.6.orig/include/linux/rmap.h
+++ linux-2.6/include/linux/rmap.h
@@ -100,6 +100,13 @@ static inline void anon_vma_merge(struct
unlink_anon_vmas(next);
}
+struct anon_vma *anon_vma_get(struct page *page);
+static inline void anon_vma_put(struct anon_vma *anon_vma)
+{
+ if (atomic_dec_and_test(&anon_vma->ref))
+ anon_vma_free(anon_vma);
+}
+
/*
* rmap interfaces called when adding or removing pte of page
*/
Index: linux-2.6/mm/ksm.c
===================================================================
--- linux-2.6.orig/mm/ksm.c
+++ linux-2.6/mm/ksm.c
@@ -323,14 +323,7 @@ static void hold_anon_vma(struct rmap_it
static void drop_anon_vma(struct rmap_item *rmap_item)
{
- struct anon_vma *anon_vma = rmap_item->anon_vma;
-
- if (atomic_dec_and_lock(&anon_vma->ref, &anon_vma->lock)) {
- int empty = list_empty(&anon_vma->head);
- spin_unlock(&anon_vma->lock);
- if (empty)
- anon_vma_free(anon_vma);
- }
+ anon_vma_put(rmap_item->anon_vma);
}
/*
Index: ...
