Re: [PATCH v4 13/14] qmp: Include "reserve" property of memory backends

From: Markus Armbruster <armbru@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: "Marcel Apfelbaum" <mapfelba@redhat.com>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Igor Kotrasinski" <i.kotrasinsk@partner.samsung.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org, "Peter Xu" <peterx@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Greg Kurz" <groug@kaod.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Murilo Opsfelder Araujo" <muriloo@linux.ibm.com>,
	"Igor Mammedov" <imammedo@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: [PATCH v4 13/14] qmp: Include "reserve" property of memory backends
Date: Fri, 19 Mar 2021 16:40:08 +0100	[thread overview]
Message-ID: <87ft0ri23r.fsf@dusky.pond.sub.org> (raw)
In-Reply-To: <20210319101230.21531-14-david@redhat.com> (David Hildenbrand's message of "Fri, 19 Mar 2021 11:12:29 +0100")

David Hildenbrand <david@redhat.com> writes:

> Let's include the new property.
>
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/core/machine-qmp-cmds.c | 1 +
>  qapi/machine.json          | 6 ++++++
>  2 files changed, 7 insertions(+)
>
> diff --git a/hw/core/machine-qmp-cmds.c b/hw/core/machine-qmp-cmds.c
> index 68a942595a..bd2a7f2dd0 100644
> --- a/hw/core/machine-qmp-cmds.c
> +++ b/hw/core/machine-qmp-cmds.c
> @@ -174,6 +174,7 @@ static int query_memdev(Object *obj, void *opaque)
>          m->merge = object_property_get_bool(obj, "merge", &error_abort);
>          m->dump = object_property_get_bool(obj, "dump", &error_abort);
>          m->prealloc = object_property_get_bool(obj, "prealloc", &error_abort);
> +        m->reserve = object_property_get_bool(obj, "reserve", &error_abort);
>          m->policy = object_property_get_enum(obj, "policy", "HostMemPolicy",
>                                               &error_abort);
>          host_nodes = object_property_get_qobject(obj,
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c0c52aef10..12860a1f79 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -814,6 +814,11 @@
>  #
>  # @prealloc: enables or disables memory preallocation
>  #
> +# @reserve: enables or disables reservation of swap space (or huge pages
> +#           if applicable). If reservation is enabled (default), actual
> +#           reservation depends on underlying OS support. In contrast,
> +#           disabling reservation without OS support will bail out. (since 6.1)
> +#

Provides two settings: "enable reservation if possible", and "disable
reservation or else fail".

Does "enable reservation or else fail" make no sense, or is it merely
unimplemented?

>  # @host-nodes: host nodes for its memory policy
>  #
>  # @policy: memory policy of memory backend
> @@ -827,6 +832,7 @@
>      'merge':      'bool',
>      'dump':       'bool',
>      'prealloc':   'bool',
> +    'reserve':    'bool',
>      'host-nodes': ['uint16'],
>      'policy':     'HostMemPolicy' }}