On Thu 04-03-21 07:40:53, Zhou Guanghui wrote: > As described in the split_page function comment, for the non-compound > high order page, the sub-pages must be freed individually. If the > memcg of the fisrt 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 split page. >
As already mentioned there are at least two explicit users of __GFP_ACCOUNT with alloc_exact_pages added recently. It would be good to mention that explicitly and maybe even mention 7efe8ef274024 resp. c419621873713 so that it is clear this is not just a theoretical issue. > Signed-off-by: Zhou Guanghui <zhouguangh...@huawei.com> Acked-by: Michal Hocko <mho...@suse.com> > --- > mm/page_alloc.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3e4b29ee2b1e..3ed783e25c3c 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3310,6 +3310,7 @@ 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); > > -- > 2.25.0 > -- Michal Hocko SUSE Labs
