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

[David Hildenbrand]

On 05.03.21 16:51, Peter Xu wrote:
> 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.

I'll probably go with

/* Map PROT_READ instead of PROT_READ|PROT_WRITE. */
#define QEMU_RAM_MMAP_READONLY      (1 << 0)

/* Map MAP_SHARED instead of MAP_PRIVATE. */
#define QEMU_RAM_MMAP_SHARED        (1 << 1)

/* Map MAP_SYNC|MAP_SHARED_VALIDATE if possible, fallback and warn otherwise. */
#define QEMU_RAM_MMAP_PMEM          (1 << 2)


for qemu_ram_mmap(). qemu_anon_ram_alloc() will still have bools, but
there it will at least be only two.

--
Thanks,

David / dhildenb