linux-kernel - [PATCH 5.10 002/221] mm/memcg: set memcg when splitting page

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Message-Id: <20210329075629.257262010@linuxfoundation.org>
Date:   Mon, 29 Mar 2021 09:55:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zhou Guanghui <zhouguanghui1@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Hugh Dickins <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Rui Xiang <rui.xiang@...wei.com>,
        Tianhong Ding <dingtianhong@...wei.com>,
        Weilong Chen <chenweilong@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.10 002/221] mm/memcg: set memcg when splitting page

From: Zhou Guanghui <zhouguanghui1@...wei.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@...wei.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Reviewed-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Hanjun Guo <guohanjun@...wei.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Rui Xiang <rui.xiang@...wei.com>
Cc: Tianhong Ding <dingtianhong@...wei.com>
Cc: Weilong Chen <chenweilong@...wei.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);