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Fri, 30 Apr 2021 12:52:33 -0700 (PDT) Received: by zeus.lespinasse.org (Postfix, from userid 1000) id A135219F524; Fri, 30 Apr 2021 12:52:33 -0700 (PDT) From: Michel Lespinasse To: Linux-MM , Linux-Kernel Cc: Laurent Dufour , Peter Zijlstra , Michal Hocko , Matthew Wilcox , Rik van Riel , Paul McKenney , Andrew Morton , Suren Baghdasaryan , Joel Fernandes , Andy Lutomirski , Michel Lespinasse Subject: [PATCH 25/29] mm: disable speculative faults for single threaded user space Date: Fri, 30 Apr 2021 12:52:26 -0700 Message-Id: <20210430195232.30491-26-michel@lespinasse.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210430195232.30491-1-michel@lespinasse.org> References: <20210430195232.30491-1-michel@lespinasse.org> MIME-Version: 1.0 Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=lespinasse.org header.s=srv-14-ed header.b=cHUjMGrj; dkim=pass header.d=lespinasse.org header.s=srv-14-rsa header.b=UOOGCy41; spf=pass (imf18.hostedemail.com: domain of walken@lespinasse.org designates 63.205.204.226 as permitted sender) smtp.mailfrom=walken@lespinasse.org; dmarc=pass (policy=none) header.from=lespinasse.org X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4B91A200027C X-Stat-Signature: dnmse59a9zfdxstpc37fgsq3164n6ygt Received-SPF: none (lespinasse.org>: No applicable sender policy available) receiver=imf18; identity=mailfrom; envelope-from=""; helo=server.lespinasse.org; client-ip=63.205.204.226 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619812359-394053 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: Performance tuning: single threaded userspace does not benefit from speculative page faults, so we turn them off to avoid any related (small) extra overheads. Signed-off-by: Michel Lespinasse --- arch/x86/mm/fault.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 463061186827..b5c21585e35f 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1321,6 +1321,14 @@ void do_user_addr_fault(struct pt_regs *regs, #endif #ifdef CONFIG_SPECULATIVE_PAGE_FAULT + + /* + * No need to try speculative faults for kernel or + * single threaded user space. + */ + if (!(flags & FAULT_FLAG_USER) || atomic_read(&mm->mm_users) == 1) + goto no_spf; + count_vm_event(SPF_ATTEMPT); seq = mmap_seq_read_start(mm); if (seq & 1) @@ -1353,7 +1361,9 @@ void do_user_addr_fault(struct pt_regs *regs, spf_abort: count_vm_event(SPF_ABORT); -#endif +no_spf: + +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */ /* * Kernel-mode access to the user address space should only occur