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[209.85.208.182]) by smtp.gmail.com with ESMTPSA id n7sm438581lji.97.2020.07.24.12.27.53 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jul 2020 12:27:54 -0700 (PDT) Received: by mail-lj1-f182.google.com with SMTP id d17so11091205ljl.3 for ; Fri, 24 Jul 2020 12:27:53 -0700 (PDT) X-Received: by 2002:a05:651c:1b6:: with SMTP id c22mr4412051ljn.421.1595618873494; Fri, 24 Jul 2020 12:27:53 -0700 (PDT) MIME-Version: 1.0 References: <20200723211432.b31831a0df3bc2cbdae31b40@linux-foundation.org> <20200724041508.QlTbrHnfh%akpm@linux-foundation.org> In-Reply-To: <20200724041508.QlTbrHnfh%akpm@linux-foundation.org> From: Linus Torvalds Date: Fri, 24 Jul 2020 12:27:37 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 01/15] mm/memory.c: avoid access flag update TLB flush for retried page fault To: Andrew Morton Cc: Catalin Marinas , Johannes Weiner , Hillf Danton , Hugh Dickins , Josef Bacik , "Kirill A . Shutemov" , Linux-MM , mm-commits@vger.kernel.org, Will Deacon , Matthew Wilcox , xuyu@linux.alibaba.com, yang.shi@linux.alibaba.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: E5D3A23260 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000198, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 23, 2020 at 9:15 PM Andrew Morton wrote: > > } > + > + if ((vmf->flags & FAULT_FLAG_WRITE) && !(vmf->flags & FAULT_FLAG_TRIED)) > + entry = pte_mkdirty(entry); > + else if (vmf->flags & FAULT_FLAG_TRIED) > + goto unlock; > + What? No. Not even with the folded update do I want this. The notion of "this is a retry, so let's do nothing" is fundamentally wrong. It makes no sense. It *may* make sense to say "ok, don't bother flushing the TLB if this is a retry, because we already did that originally". MAYBE. I'm dropping this patch as incomprehensible, with or without the cleaned-up mversion. Linus