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. -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>