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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1r6PJJ-008Gcb-3y; Fri, 24 Nov 2023 06:05:05 +0000 Date: Fri, 24 Nov 2023 06:05:05 +0000 From: Matthew Wilcox To: Peng Zhang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, fengwei.yin@intel.com, ying.huang@intel.com, aneesh.kumar@linux.ibm.com, shy828301@gmail.com, hughd@google.com, david@redhat.com, wangkefeng.wang@huawei.com, sunnanyong@huawei.com Subject: Re: [RFC PATCH] mm: filemap: avoid unnecessary major faults in filemap_fault() Message-ID: References: <20231122140052.4092083-1-zhangpeng362@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231122140052.4092083-1-zhangpeng362@huawei.com> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 29E1F40020 X-Stat-Signature: fo3u4gc4wfz49t8owkd1h14bazta5uar X-Rspam-User: X-HE-Tag: 1700805911-664046 X-HE-Meta: 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 8vG/W1AF jMk4ZeftRGmDQMGJEXsz/I1r0s0gIewhY3R/vqHdhldocek0RDnMNuI3ePk0bqir5Z8EqAmY72xUlrwtr6DMP39fXDrtacoZ10ThVrzWN6WeYrDkLe0Ro/UyuAT/qmFB18wu4lojKwRXhoZn1Si/Y64D5oeUPt675zGwGouDj4yhB8Pbd1fWVnUvhjOD0CwQon63g/XVOBhokl7PwuMc8Cbgpsg== 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 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. 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; } /*