On Thu, Aug 09 2012, Glauber Costa wrote:
> When a process tries to allocate a page with the __GFP_KMEMCG flag, the
> page allocator will call the corresponding memcg functions to validate
> the allocation. Tasks in the root memcg can always proceed.
>
> To avoid adding markers to the page - and a kmem flag that would
> necessarily follow, as much as doing page_cgroup lookups for no reason,
> whoever is marking its allocations with __GFP_KMEMCG flag is responsible
> for telling the page allocator that this is such an allocation at
> free_pages() time. This is done by the invocation of
> __free_accounted_pages() and free_accounted_pages().
>
> Signed-off-by: Glauber Costa <glom...@parallels.com>
> CC: Christoph Lameter <c...@linux.com>
> CC: Pekka Enberg <penb...@cs.helsinki.fi>
> CC: Michal Hocko <mho...@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hir...@jp.fujitsu.com>
> CC: Johannes Weiner <han...@cmpxchg.org>
> CC: Suleiman Souhlal <sulei...@google.com>
> ---
> include/linux/gfp.h | 3 +++
> mm/page_alloc.c | 38 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 41 insertions(+)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index d8eae4d..029570f 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -370,6 +370,9 @@ extern void free_pages(unsigned long addr, unsigned int
> order);
> extern void free_hot_cold_page(struct page *page, int cold);
> extern void free_hot_cold_page_list(struct list_head *list, int cold);
>
> +extern void __free_accounted_pages(struct page *page, unsigned int order);
> +extern void free_accounted_pages(unsigned long addr, unsigned int order);
> +
> #define __free_page(page) __free_pages((page), 0)
> #define free_page(addr) free_pages((addr), 0)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b956cec..da341dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2532,6 +2532,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int
> order,
> struct page *page = NULL;
> int migratetype = allocflags_to_migratetype(gfp_mask);
> unsigned int cpuset_mems_cookie;
> + void *handle = NULL;
>
> gfp_mask &= gfp_allowed_mask;
>
> @@ -2543,6 +2544,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int
> order,
> return NULL;
>
> /*
> + * Will only have any effect when __GFP_KMEMCG is set.
> + * This is verified in the (always inline) callee
> + */
> + if (!memcg_kmem_new_page(gfp_mask, &handle, order))
> + return NULL;
> +
> + /*
> * Check the zones suitable for the gfp_mask contain at least one
> * valid zone. It's possible to have an empty zonelist as a result
> * of GFP_THISNODE and a memoryless node
If memcg_kmem_new_page() succeeds then it may have obtained a memcg
reference with mem_cgroup_get(). I think this reference is leaked when
returning below:
/*
* Check the zones suitable for the gfp_mask contain at least one
* valid zone. It's possible to have an empty zonelist as a result
* of GFP_THISNODE and a memoryless node
*/
if (unlikely(!zonelist->_zonerefs->zone))
return NULL;
I suspect the easiest fix is to swap the call to memcg_kmem_new_page()
and the (!zonelist->_zonerefs->zone) check.
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