From: Zhou Guanghui zhouguanghui1@huawei.com
commit e1baddf8475b06cc56f4bafecf9a32a124343d9f upstream.
As described in the split_page() comment, for the non-compound high order page, the sub-pages must be freed individually. If the memcg of the first page is valid, the tail pages cannot be uncharged when be freed.
For example, when alloc_pages_exact is used to allocate 1MB continuous physical memory, 2MB is charged(kmemcg is enabled and __GFP_ACCOUNT is set). When make_alloc_exact free the unused 1MB and free_pages_exact free the applied 1MB, actually, only 4KB(one page) is uncharged.
Therefore, the memcg of the tail page needs to be set when splitting a page.
Michel:
There are at least two explicit users of __GFP_ACCOUNT with alloc_exact_pages added recently. See 7efe8ef274024 ("KVM: arm64: Allocate stage-2 pgd pages with GFP_KERNEL_ACCOUNT") and c419621873713 ("KVM: s390: Add memcg accounting to KVM allocations"), so this is not just a theoretical issue.
Link: https://lkml.kernel.org/r/20210304074053.65527-3-zhouguanghui1@huawei.com Signed-off-by: Zhou Guanghui zhouguanghui1@huawei.com Acked-by: Johannes Weiner hannes@cmpxchg.org Reviewed-by: Zi Yan ziy@nvidia.com Reviewed-by: Shakeel Butt shakeelb@google.com Acked-by: Michal Hocko mhocko@suse.com Cc: Hanjun Guo guohanjun@huawei.com Cc: Hugh Dickins hughd@google.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Cc: Nicholas Piggin npiggin@gmail.com Cc: Rui Xiang rui.xiang@huawei.com Cc: Tianhong Ding dingtianhong@huawei.com Cc: Weilong Chen chenweilong@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/page_alloc.c | 1 + 1 file changed, 1 insertion(+)
--- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3272,6 +3272,7 @@ void split_page(struct page *page, unsig for (i = 1; i < (1 << order); i++) set_page_refcounted(page + i); split_page_owner(page, 1 << order); + split_page_memcg(page, 1 << order); } EXPORT_SYMBOL_GPL(split_page);