From e1baddf8475b06cc56f4bafecf9a32a124343d9f Mon Sep 17 00:00:00 2001 From: Zhou Guanghui Date: Fri, 12 Mar 2021 21:08:33 -0800 Subject: mm/memcg: set memcg when splitting page 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 Acked-by: Johannes Weiner Reviewed-by: Zi Yan Reviewed-by: Shakeel Butt Acked-by: Michal Hocko Cc: Hanjun Guo Cc: Hugh Dickins Cc: Kefeng Wang Cc: "Kirill A. Shutemov" Cc: Nicholas Piggin Cc: Rui Xiang Cc: Tianhong Ding Cc: Weilong Chen Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 1 + 1 file changed, 1 insertion(+) (limited to 'mm') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3cd1c0ce4d06..cfc72873961d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3314,6 +3314,7 @@ void split_page(struct page *page, unsigned int order) 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); -- cgit v1.2.3