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Thu, 04 Mar 2021 07:52:10 -0800 (PST) Received: from localhost ([2620:10d:c091:480::1:b28e]) by smtp.gmail.com with ESMTPSA id a9sm17591946qtx.96.2021.03.04.07.52.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Mar 2021 07:52:10 -0800 (PST) Date: Thu, 4 Mar 2021 10:52:09 -0500 From: Johannes Weiner To: Zhou Guanghui Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@suse.com, hughd@google.com, kirill.shutemov@linux.intel.com, npiggin@gmail.com, ziy@nvidia.com, wangkefeng.wang@huawei.com, guohanjun@huawei.com, dingtianhong@huawei.com, chenweilong@huawei.com, rui.xiang@huawei.com Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page Message-ID: References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-3-zhouguanghui1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210304074053.65527-3-zhouguanghui1@huawei.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: EC506A0009E5 X-Stat-Signature: m7hqxt9yg3rbbkoeghfx7i5ccakjfben Received-SPF: none (cmpxchg.org>: No applicable sender policy available) receiver=imf23; identity=mailfrom; envelope-from=""; helo=mail-qk1-f173.google.com; client-ip=209.85.222.173 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614873130-234552 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. > > Signed-off-by: Zhou Guanghui Acked-by: Johannes Weiner