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

[David Hildenbrand <david@redhat.com>]

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