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([2001:b07:6468:f312:3c1c:ffba:c624:29b8]) by smtp.gmail.com with ESMTPSA id b16sm2927189ejg.43.2020.05.27.06.06.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 May 2020 06:06:31 -0700 (PDT) Subject: Re: [PATCH v3 14/22] microvm: use 2G split unconditionally To: Igor Mammedov , Gerd Hoffmann References: <20200520132003.9492-1-kraxel@redhat.com> <20200520132003.9492-15-kraxel@redhat.com> <20200521112921.641f12bb@redhat.com> <20200525114508.hhvyzjiqja6knz6l@sirius.home.kraxel.org> <20200525183615.5f8e67d3@redhat.com> <20200526044839.bncj6iltugnzgfmy@sirius.home.kraxel.org> <20200527142545.32e91049@redhat.com> From: Paolo Bonzini Message-ID: <58ced517-1ad4-c895-afe6-fec690791f4f@redhat.com> Date: Wed, 27 May 2020 15:06:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200527142545.32e91049@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 05:46:19 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Eduardo Habkost , Sergio Lopez , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Shannon Zhao , qemu-arm@nongnu.org, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 27/05/20 14:25, Igor Mammedov wrote: >> (2) we loose a gigabyte page. > I'm not sure waht exactly we loose in this case. > Lets assume we allocating guest 5G of continuous RAM using 1G huge pages, > in this case I'd think that on host side MMIO overlay won't affect RAM blob > on guest side pagetables will be fragmented due to MMIO holes, but guest still > could use huge pages smaller ones in fragmented area and 1G where there is no fragmentation. Access to the 3G-4G area would not be able to use 1G EPT pages. But why use 2G split instead of 3G? There's only very little MMIO and no PCI hole (including no huge MMCONFIG BAR) on microvm. Paolo