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[174.95.95.253]) by smtp.gmail.com with ESMTPSA id a9sm1995727qtx.96.2021.03.05.07.37.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Mar 2021 07:37:15 -0800 (PST) Date: Fri, 5 Mar 2021 10:37:13 -0500 From: Peter Xu To: David Hildenbrand Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" , Eduardo Habkost , "Dr. David Alan Gilbert" , Richard Henderson , Paolo Bonzini , Igor Mammedov , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Stefan Hajnoczi , Murilo Opsfelder Araujo , Greg Kurz , Liam Merwick , Christian Borntraeger , Cornelia Huck , Halil Pasic , Igor Kotrasinski , Juan Quintela , Stefan Weil , Thomas Huth , kvm@vger.kernel.org, qemu-s390x@nongnu.org Subject: Re: [PATCH v2 7/9] memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap() Message-ID: <20210305153713.GG397383@xz-x1> References: <20210305101634.10745-1-david@redhat.com> <20210305101634.10745-8-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210305101634.10745-8-david@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Mar 05, 2021 at 11:16:32AM +0100, David Hildenbrand wrote: > Let's introduce RAM_NORESERVE, allowing mmap'ing with MAP_NORESERVE. The > new flag has the following semantics: > > RAM is mmap-ed with MAP_NORESERVE. When set, reserving swap space (or > huge pages on Linux) is skipped: will bail out if not supported. When not > set, the OS might reserve swap space (or huge pages on Linux), depending > on OS support. > > Allow passing it into: > - memory_region_init_ram_nomigrate() > - memory_region_init_resizeable_ram() > - memory_region_init_ram_from_file() > > ... and teach qemu_ram_mmap() and qemu_anon_ram_alloc() about the flag. > Bail out if the flag is not supported, which is the case right now for > both, POSIX and win32. We will add the POSIX mmap implementation next and > allow specifying RAM_NORESERVE via memory backends. > > The target use case is virtio-mem, which dynamically exposes memory > inside a large, sparse memory area to the VM. > > Cc: Juan Quintela > Cc: Halil Pasic > Cc: Cornelia Huck > Cc: Christian Borntraeger > Cc: Thomas Huth > Cc: Stefan Weil > Cc: kvm@vger.kernel.org > Cc: qemu-s390x@nongnu.org > Signed-off-by: David Hildenbrand Reviewed-by: Peter Xu -- Peter Xu