linux-kernel - [PATCH v2 2/2] mm/memcg: set memcg when split page

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Date:   Thu, 4 Mar 2021 07:40:53 +0000
From:   Zhou Guanghui <zhouguanghui1@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC:     <akpm@...ux-foundation.org>, <mhocko@...e.com>,
        <hannes@...xchg.org>, <hughd@...gle.com>,
        <kirill.shutemov@...ux.intel.com>, <npiggin@...il.com>,
        <ziy@...dia.com>, <wangkefeng.wang@...wei.com>,
        <guohanjun@...wei.com>, <dingtianhong@...wei.com>,
        <chenweilong@...wei.com>, <rui.xiang@...wei.com>
Subject: [PATCH v2 2/2] mm/memcg: set memcg when split page

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.

Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.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