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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id r7sm423915qtw.17.2021.03.10.14.00.33 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Wed, 10 Mar 2021 14:00:34 -0800 (PST) Date: Wed, 10 Mar 2021 14:00:18 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: "Singh, Balbir" cc: Michal Hocko , 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 Subject: Re: [PATCH v2 1/2] mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg In-Reply-To: Message-ID: References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-2-zhouguanghui1@huawei.com> <3ad50842-881f-eb88-a14d-0b6c70ce33d2@gmail.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Stat-Signature: dqbwz17g1d9uxrp1d5k16ayngrriq99t X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3D2752381 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf04; identity=mailfrom; envelope-from=""; helo=mail-qk1-f171.google.com; client-ip=209.85.222.171 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615413635-422211 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, 11 Mar 2021, Singh, Balbir wrote: > 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. I think you imagine this is something it's not. "all callers" are __split_huge_page() and split_page() (maybe Matthew will have a third caller, maybe not). It is not something drivers will be calling directly themselves, and it won't ever get EXPORTed to them. Hugh