Re: [PATCH v2 7/9] memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()

From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Igor Mammedov" <imammedo@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Murilo Opsfelder Araujo" <muriloo@linux.ibm.com>,
	"Greg Kurz" <groug@kaod.org>,
	"Liam Merwick" <liam.merwick@oracle.com>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Halil Pasic" <pasic@linux.ibm.com>,
	"Igor Kotrasinski" <i.kotrasinsk@partner.samsung.com>,
	"Juan Quintela" <quintela@redhat.com>,
	"Stefan Weil" <sw@weilnetz.de>, "Thomas Huth" <thuth@redhat.com>,
	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()
Date: Fri, 5 Mar 2021 10:37:13 -0500	[thread overview]
Message-ID: <20210305153713.GG397383@xz-x1> (raw)
In-Reply-To: <20210305101634.10745-8-david@redhat.com>

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 <quintela@redhat.com>
> Cc: Halil Pasic <pasic@linux.ibm.com>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: Stefan Weil <sw@weilnetz.de>
> Cc: kvm@vger.kernel.org
> Cc: qemu-s390x@nongnu.org
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu