On 08/09/2012 08:33 PM, Greg Thelen wrote: > 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. > You are right, indeed.
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