On 05/13/2010 07:26 AM, Mel Gorman wrote:
On Wed, May 12, 2010 at 05:09:18PM -0400, Rik van Riel wrote:
On 05/12/2010 05:07 PM, Mel Gorman wrote:
On Wed, May 12, 2010 at 01:41:11PM -0400, Rik van Riel wrote:
Subject: extend KSM refcounts to the anon_vma root
KSM reference counts can cause an anon_vma to exist after the processe
it belongs to have already exited. Because the anon_vma lock now lives
in the root anon_vma, we need to ensure that the root anon_vma stays
around until after all the "child" anon_vmas have been freed.
The obvious way to do this is to have a "child" anon_vma take a
reference to the root in anon_vma_fork. When the anon_vma is freed
at munmap or process exit, we drop the refcount in anon_vma_unlink
and possibly free the root anon_vma.
The KSM anon_vma reference count function also needs to be modified
to deal with the possibility of freeing 2 levels of anon_vma. The
easiest way to do this is to break out the KSM magic and make it
generic.
When compiling without CONFIG_KSM, this code is compiled out.
Signed-off-by: Rik van Riel<riel@xxxxxxxxxx>
---
include/linux/rmap.h | 12 ++++++++++++
mm/ksm.c | 17 ++++++-----------
mm/rmap.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 62 insertions(+), 12 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 33ffe14..387d40c 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -126,6 +126,18 @@ int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *);
void __anon_vma_link(struct vm_area_struct *);
void anon_vma_free(struct anon_vma *);
+#ifdef CONFIG_KSM
+static inline void get_anon_vma(struct anon_vma *anon_vma)
+{
+ atomic_inc(&anon_vma->ksm_refcount);
+}
+
+void drop_anon_vma(struct anon_vma *);
+#else
+#define get_anon_vma(x) do {} while(0)
+#define drop_anon_vma(x) do {} while(0)
+#endif
+
static inline void anon_vma_merge(struct vm_area_struct *vma,
struct vm_area_struct *next)
{
diff --git a/mm/ksm.c b/mm/ksm.c
index 7ca0dd7..9f2acc9 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -318,19 +318,14 @@ static void hold_anon_vma(struct rmap_item *rmap_item,
struct anon_vma *anon_vma)
{
rmap_item->anon_vma = anon_vma;
- atomic_inc(&anon_vma->ksm_refcount);
+ get_anon_vma(anon_vma);
}
I'm not quite getting this. Here, we get the local anon_vma so we
increment its reference count and later we drop it but without a
refcount taken on the root anon_vma, why is it guaranteed to stay
around?
Because anon_vma_fork takes a reference count on the root anon_vma,
the VMA we take a refcount on will either have a refcount on the
root, or it is the root.
Sorry, I'm still not getting it. anon_vma_fork keeps the refcount around
during fork but what about during exit?
It is kept around all the way from fork until exit.
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