On Thu, Mar 04, 2021 at 07:40:53AM +0000, 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.
There's another place we need to do this to ...
+++ b/mm/page_alloc.c
@@ -5081,9 +5081,15 @@ void __free_pages(struct page *page, unsigned int order)
{
if (put_page_testzero(page))
free_the_page(page, order);
- else if (!PageHead(page))
- while (order-- > 0)
- free_the_page(page + (1 << order), order);
+ else if (!PageHead(page)) {
+ while (order-- > 0) {
+ struct page *tail = page + (1 << order);
+#ifdef CONFIG_MEMCG
+ tail->memcg_data = page->memcg_data;
+#endif
+ free_the_page(tail, order);
+ }
+ }
}
EXPORT_SYMBOL(__free_pages);
I wonder if we shouldn't initialise memcg_data on all subsequent pages
of non-compound allocations instead? Because I'm not sure this is the
only place that needs to be fixed.
