Re: [PATCH v2 8/9] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE

From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: "Thomas Huth" <thuth@redhat.com>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Stefan Weil" <sw@weilnetz.de>,
	"Murilo Opsfelder Araujo" <muriloo@linux.ibm.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Juan Quintela" <quintela@redhat.com>,
	qemu-devel@nongnu.org, "Halil Pasic" <pasic@linux.ibm.com>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Greg Kurz" <groug@kaod.org>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Igor Mammedov" <imammedo@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Igor Kotrasinski" <i.kotrasinsk@partner.samsung.com>
Subject: Re: [PATCH v2 8/9] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE
Date: Fri, 5 Mar 2021 10:51:41 -0500	[thread overview]
Message-ID: <20210305155141.GI397383@xz-x1> (raw)
In-Reply-To: <f577f691-9bdc-a435-9f20-1de62be2241e@redhat.com>

On Fri, Mar 05, 2021 at 04:44:36PM +0100, David Hildenbrand wrote:
> On 05.03.21 16:42, Peter Xu wrote:
> > On Fri, Mar 05, 2021 at 11:16:33AM +0100, David Hildenbrand wrote:
> > > +#define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory"
> > > +static bool map_noreserve_effective(int fd, bool readonly, bool shared)
> > > +{
> > 
> > [...]
> > 
> > > @@ -184,8 +251,7 @@ void *qemu_ram_mmap(int fd,
> > >       size_t offset, total;
> > >       void *ptr, *guardptr;
> > > -    if (noreserve) {
> > > -        error_report("Skipping reservation of swap space is not supported");
> > > +    if (noreserve && !map_noreserve_effective(fd, shared, readonly)) {
> > 
> > Need to switch "shared" & "readonly"?
> 
> Indeed, interestingly it has the same effect (as we don't have anonymous
> read-only memory in QEMU :) )

But note there is still a "g_assert(!shared || fd >= 0);" inside.. :)

> 
> (wouldn't have happened with flags  ... hmm)

Right.

-- 
Peter Xu