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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-841367f32besm801295241.40.2024.08.12.11.58.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Aug 2024 11:58:10 -0700 (PDT) Date: Mon, 12 Aug 2024 14:58:07 -0400 From: Peter Xu To: Axel Rasmussen Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sean Christopherson , Oscar Salvador , Jason Gunthorpe , linux-arm-kernel@lists.infradead.org, x86@kernel.org, Will Deacon , Gavin Shan , Paolo Bonzini , Zi Yan , Andrew Morton , Catalin Marinas , Ingo Molnar , Alistair Popple , Borislav Petkov , David Hildenbrand , Thomas Gleixner , kvm@vger.kernel.org, Dave Hansen , Alex Williamson , Yan Zhao Subject: Re: [PATCH 10/19] KVM: Use follow_pfnmap API Message-ID: References: <20240809160909.1023470-1-peterx@redhat.com> <20240809160909.1023470-11-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Stat-Signature: fgzqbywsc3dsjb6gsxbjtfobq73rnoxc X-Rspamd-Queue-Id: 94FCA20015 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1723489093-342603 X-HE-Meta: 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 jmu+vGTG 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 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 Fri, Aug 09, 2024 at 10:23:20AM -0700, Axel Rasmussen wrote: > On Fri, Aug 9, 2024 at 9:09 AM Peter Xu wrote: > > > > Use the new pfnmap API to allow huge MMIO mappings for VMs. The rest work > > is done perfectly on the other side (host_pfn_mapping_level()). > > I don't think it has to be done in this series, but a future > optimization to consider is having follow_pfnmap just tell the caller > about the mapping level directly. It already found this information as > part of its walk. I think there's a possibility to simplify KVM / > avoid it having to do its own walk again later. AFAIU pfnmap isn't special in this case, as we do the "walk pgtable twice" idea also to a generic page here, so probably not directly relevant to this patch alone. But I agree with you, sounds like something we can consider trying. I would be curious on whether the perf difference would be measurable in this specific case, though. I mean, this first walk will heat up all the things, so I'd expect the 2nd walk (which is lockless) later be pretty fast normally. Thanks, -- Peter Xu