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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id m34sm2754046otc.25.2021.03.02.12.24.52 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Tue, 02 Mar 2021 12:24:53 -0800 (PST) Date: Tue, 2 Mar 2021 12:24:41 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Zhou Guanghui cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, wangkefeng.wang@huawei.com, guohanjun@huawei.com, dingtianhong@huawei.com, chenweilong@huawei.com, rui.xiang@huawei.com, Johannes Weiner , Nicholas Piggin , "Kirill A. Shutemov" , Hugh Dickins Subject: Re: [PATCH] mm/memcg: set memcg when split pages In-Reply-To: Message-ID: References: <20210302013451.118701-1-zhouguanghui1@huawei.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2 Mar 2021, Michal Hocko wrote: > [Cc Johannes for awareness and fixup Nick's email] > > On Tue 02-03-21 01:34:51, Zhou Guanghui wrote: > > When split page, the memory cgroup info recorded in first page is > > not copied to tail pages. In this case, when the tail pages are > > freed, the uncharge operation is not performed. As a result, the > > usage of this memcg keeps increasing, and the OOM may occur. > > > > So, the copying of first page's memory cgroup info to tail pages > > is needed when split page. > > I was not aware that alloc_pages_exact is used for accounted allocations > but git grep told me otherwise so this is not a theoretical one. Both > users (arm64 and s390 kvm) are quite recent AFAICS. split_page is also > used in dma allocator but I got lost in indirection so I have no idea > whether there are any users there. Yes, it's a bit worrying that such a low-level thing as split_page() can now get caught up in memcg accounting, but I suppose that's okay. I feel rather strongly that whichever way it is done, THP splitting and split_page() should use the same interface to memcg. And a look at mem_cgroup_split_huge_fixup() suggests that nowadays there need to be css_get()s too - or better, a css_get_many(). Its #ifdef CONFIG_TRANSPARENT_HUGEPAGE should be removed, rename it mem_cgroup_split_page_fixup(), and take order from caller. Though I've never much liked that separate pass: would it be better page by page, like this copy_page_memcg() does? Though mem_cgroup_disabled() and css_getting make that less appealing. Hugh > > The page itself looks reasonable to me. > > > Signed-off-by: Zhou Guanghui > > Acked-by: Michal Hocko > > Minor nit > > > --- > > include/linux/memcontrol.h | 10 ++++++++++ > > mm/page_alloc.c | 4 +++- > > 2 files changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index e6dc793d587d..c7e2b4421dc1 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -867,6 +867,12 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg); > > extern bool cgroup_memory_noswap; > > #endif > > > > +static inline void copy_page_memcg(struct page *dst, struct page *src) > > +{ > > + if (src->memcg_data) > > + dst->memcg_data = src->memcg_data; > > I would just drop the test. The struct page is a single cache line which > is dirty by the reference count so another store will unlikely be > noticeable even when NULL is stored here and you safe a conditional. > > > +} > > + > > struct mem_cgroup *lock_page_memcg(struct page *page); > > void __unlock_page_memcg(struct mem_cgroup *memcg); > > void unlock_page_memcg(struct page *page); > > @@ -1291,6 +1297,10 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > > { > > } > > > > +static inline void copy_page_memcg(struct page *dst, struct page *src) > > +{ > > +} > > + > > static inline struct mem_cgroup *lock_page_memcg(struct page *page) > > { > > return NULL; > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 3e4b29ee2b1e..ee0a63dc1c9b 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3307,8 +3307,10 @@ void split_page(struct page *page, unsigned int order) > > VM_BUG_ON_PAGE(PageCompound(page), page); > > VM_BUG_ON_PAGE(!page_count(page), page); > > > > - for (i = 1; i < (1 << order); i++) > > + for (i = 1; i < (1 << order); i++) { > > set_page_refcounted(page + i); > > + copy_page_memcg(page + i, page); > > + } > > split_page_owner(page, 1 << order); > > } > > EXPORT_SYMBOL_GPL(split_page); > > -- > > 2.25.0 > > > > -- > Michal Hocko > SUSE Labs