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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [RFC PATCH] mm: filemap: avoid unnecessary major faults in filemap_fault() Content-Language: en-US To: Matthew Wilcox CC: , , , , , , , , , , References: <20231122140052.4092083-1-zhangpeng362@huawei.com> From: "zhangpeng (AS)" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.160] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemm000020.china.huawei.com (7.193.23.93) X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: 92A9A120008 X-Rspam-User: X-Stat-Signature: 9x49huajsmcr53h871j6eztotnfatspq X-Rspamd-Server: rspam03 X-HE-Tag: 1700811801-845992 X-HE-Meta: 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 ittwK6Ry vJxVHCmUKywgnKqgg/zSJSPh9FUATpDD9oeiyJXgKdZd9wsGtbPmAc9lTphqiK+elXowpM9XiM+iL8roxg+ZApslV6FDsfpIgbPkJEflRrMYmcqSEDWxj9l9ep6UtjnVzbknapbbNorZwmhJiCsO5FGOoeAW52t2GhTYAUxaAv71OS8t5LoDrug/304kpuIYsrX53qvzI+tUqw2E= 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: List-Subscribe: List-Unsubscribe: On 2023/11/24 14:05, Matthew Wilcox wrote: > On Wed, Nov 22, 2023 at 10:00:52PM +0800, Peng Zhang wrote: >> From: ZhangPeng >> >> The major fault occurred when using mlockall(MCL_CURRENT | MCL_FUTURE) >> in application, which leading to an unexpected performance issue[1]. >> >> This caused by temporarily cleared pte during a read/modify/write update >> of the pte, eg, do_numa_page()/change_pte_range(). > What I haven't quite understood yet is why we need to set the pte to > zero on x86 in the specific case of do_numa_page(). I understand that > ppc needs to. I'm also curious. Could ptep_modify_prot_start() of other architectures (except ppc) not clear pte? We are mainly concerned with arm64 and x86. > Could someone explain why the _default_ definition of > ptep_modify_prot_start() is not: > > +++ b/include/linux/pgtable.h > @@ -1074,7 +1074,7 @@ static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma, > unsigned long addr, > pte_t *ptep) > { > - return __ptep_modify_prot_start(vma, addr, ptep); > + return *ptep; > } > > /* > > -- Best Regards, Peng