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Wed, 10 Mar 2021 13:44:30 -0800 (PST) Received: from f8ffc2228008.ant.amazon.com ([54.240.193.1]) by smtp.gmail.com with ESMTPSA id a7sm407994pfo.105.2021.03.10.13.44.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Mar 2021 13:44:29 -0800 (PST) Subject: Re: [PATCH v2 1/2] mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg To: Michal Hocko Cc: Zhou Guanghui , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, hannes@cmpxchg.org, 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 References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-2-zhouguanghui1@huawei.com> <3ad50842-881f-eb88-a14d-0b6c70ce33d2@gmail.com> From: "Singh, Balbir" Message-ID: Date: Thu, 11 Mar 2021 08:44:22 +1100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Stat-Signature: ujaxyypyfxntcdqya64wyy6z89j46naf X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 466D4407F8DF Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf26; identity=mailfrom; envelope-from=""; helo=mail-pg1-f180.google.com; client-ip=209.85.215.180 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615412669-633414 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 9/3/21 7:28 pm, Michal Hocko wrote: > On Tue 09-03-21 09:37:29, Balbir Singh wrote: >> On 4/3/21 6:40 pm, Zhou Guanghui wrote: > [...] >>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> /* >>> - * Because page_memcg(head) is not set on compound tails, set it now. >>> + * Because page_memcg(head) is not set on tails, set it now. >>> */ >>> -void mem_cgroup_split_huge_fixup(struct page *head) >>> +void split_page_memcg(struct page *head, unsigned int nr) >>> { >> >> Do we need input validation on nr? Can nr be aribtrary or can we enforce >> >> VM_BUG_ON(!is_power_of_2(nr)); > > In practice this will be power of 2 but why should we bother to sanitze > that? > Just when DEBUG_VM is enabled to ensure the contract is valid, given that nr is now variable, we could end up with subtle bugs unless we can audit all callers. Even the power of 2 check does not catch the fact that nr is indeed what we expect, but it still checks a large range of invalid inputs. Balbir Singh.