[Cc Johannes for awareness and fixup Nick's email]
On Tue 02-03-21 01:34:51, Zhou Guanghui wrote:
> When split page, the memory cgroup info recorded in first page is
> not copied to tail pages. In this case, when the tail pages are
> freed, the uncharge operation is not performed. As a result, the
> usage of this memcg keeps increasing, and the OOM may occur.
>
> So, the copying of first page's memory cgroup info to tail pages
> is needed when split page.
I was not aware that alloc_pages_exact is used for accounted allocations
but git grep told me otherwise so this is not a theoretical one. Both
users (arm64 and s390 kvm) are quite recent AFAICS. split_page is also
used in dma allocator but I got lost in indirection so I have no idea
whether there are any users there.
The page itself looks reasonable to me.
> Signed-off-by: Zhou Guanghui <zhouguanghui1@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Minor nit
> ---
> include/linux/memcontrol.h | 10 ++++++++++
> mm/page_alloc.c | 4 +++-
> 2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index e6dc793d587d..c7e2b4421dc1 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -867,6 +867,12 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
> extern bool cgroup_memory_noswap;
> #endif
>
> +static inline void copy_page_memcg(struct page *dst, struct page *src)
> +{
> + if (src->memcg_data)
> + dst->memcg_data = src->memcg_data;
I would just drop the test. The struct page is a single cache line which
is dirty by the reference count so another store will unlikely be
noticeable even when NULL is stored here and you safe a conditional.
> +}
> +
> struct mem_cgroup *lock_page_memcg(struct page *page);
> void __unlock_page_memcg(struct mem_cgroup *memcg);
> void unlock_page_memcg(struct page *page);
> @@ -1291,6 +1297,10 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
> {
> }
>
> +static inline void copy_page_memcg(struct page *dst, struct page *src)
> +{
> +}
> +
> static inline struct mem_cgroup *lock_page_memcg(struct page *page)
> {
> return NULL;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3e4b29ee2b1e..ee0a63dc1c9b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3307,8 +3307,10 @@ void split_page(struct page *page, unsigned int order)
> VM_BUG_ON_PAGE(PageCompound(page), page);
> VM_BUG_ON_PAGE(!page_count(page), page);
>
> - for (i = 1; i < (1 << order); i++)
> + for (i = 1; i < (1 << order); i++) {
> set_page_refcounted(page + i);
> + copy_page_memcg(page + i, page);
> + }
> split_page_owner(page, 1 << order);
> }
> EXPORT_SYMBOL_GPL(split_page);
> --
> 2.25.0
>
--
Michal Hocko
SUSE Labs
