9181fb7043
Let's provide a way to control the use of RAM_NORESERVE via memory backends using the "reserve" property which defaults to true (old behavior). Only Linux currently supports clearing the flag (and support is checked at runtime, depending on the setting of "/proc/sys/vm/overcommit_memory"). Windows and other POSIX systems will bail out with "reserve=false". The target use case is virtio-mem, which dynamically exposes memory inside a large, sparse memory area to the VM. This essentially allows avoiding to set "/proc/sys/vm/overcommit_memory == 0") when using virtio-mem and also supporting hugetlbfs in the future. As really only Linux implements RAM_NORESERVE right now, let's expose the property only with CONFIG_LINUX. Setting the property to "false" will then only fail in corner cases -- for example on very old kernels or when memory overcommit was completely disabled by the admin. Reviewed-by: Peter Xu <peterx@redhat.com> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Acked-by: Eduardo Habkost <ehabkost@redhat.com> for memory backend and machine core Cc: Markus Armbruster <armbru@redhat.com> Cc: Eric Blake <eblake@redhat.com> Cc: Igor Mammedov <imammedo@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20210510114328.21835-11-david@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
58 lines
1.4 KiB
C
58 lines
1.4 KiB
C
/*
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* QEMU Host Memory Backend
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*
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* Copyright (C) 2013-2014 Red Hat Inc
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*
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* Authors:
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* Igor Mammedov <imammedo@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "sysemu/hostmem.h"
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#include "qapi/error.h"
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#include "qemu/module.h"
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#include "qom/object_interfaces.h"
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static void
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ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
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{
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uint32_t ram_flags;
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char *name;
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if (!backend->size) {
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error_setg(errp, "can't create backend with size 0");
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return;
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}
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name = host_memory_backend_get_name(backend);
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ram_flags = backend->share ? RAM_SHARED : 0;
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ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
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memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend), name,
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backend->size, ram_flags, errp);
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g_free(name);
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}
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static void
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ram_backend_class_init(ObjectClass *oc, void *data)
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{
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HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
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bc->alloc = ram_backend_memory_alloc;
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}
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static const TypeInfo ram_backend_info = {
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.name = TYPE_MEMORY_BACKEND_RAM,
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.parent = TYPE_MEMORY_BACKEND,
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.class_init = ram_backend_class_init,
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};
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static void register_types(void)
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{
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type_register_static(&ram_backend_info);
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}
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type_init(register_types);
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