Re: kvm userspace: ksm support

[Izik Eidus <ieidus@redhat.com>]

Brian Jackson wrote:
> On Monday 03 August 2009 01:09:38 pm Izik Eidus wrote:
>   
>> Brian Jackson wrote:
>>     
>>> If someone wanted to play around with ksm in qemu-kvm-0.x.x would it be
>>> as simple as adding the below additions to kvm_setup_guest_memory in
>>> kvm-all.c
>>>       
>> qemu-kvm-0.x.x doesnt tell me much, but if it is the function that
>> register the memory than yes...
>>
>> (I just remember that qemu used to have something called phys_ram_base,
>> in that case it would be just making madvise on phys_ram_base with the
>> same of phys_ram_size....)
>>     
>
> Sorry, I'm using qemu-kvm-0.10.6
>
>
> This is what qemu_ram_alloc looks like:
>
>
>
> /* XXX: better than nothing */
> ram_addr_t qemu_ram_alloc(ram_addr_t size)
> {
>     ram_addr_t addr;
>     if ((phys_ram_alloc_offset + size) > phys_ram_size) {
>         fprintf(stderr, "Not enough memory (requested_size = %" PRIu64 ", max memory = %" PRIu64 ")\n",
>                 (uint64_t)size, (uint64_t)phys_ram_size);
>         abort();
>     }
>     addr = phys_ram_alloc_offset;
>     phys_ram_alloc_offset = TARGET_PAGE_ALIGN(phys_ram_alloc_offset + size);
>
>     if (kvm_enabled())
>         kvm_setup_guest_memory(phys_ram_base + addr, size);
>
>     return addr;
> }
>
>
> And this is what my new kvm_setup_guest_memory looks like:
>
>
> void kvm_setup_guest_memory(void *start, size_t size)
> {
>     if (!kvm_has_sync_mmu()) {
> #ifdef MADV_DONTFORK
>         int ret = madvise(start, size, MADV_DONTFORK);
>
>         if (ret) {
>             perror("madvice");
>             exit(1);
>         }
> #else
>         fprintf(stderr,
>                 "Need MADV_DONTFORK in absence of synchronous KVM MMU\n");
>         exit(1);
> #endif
>     }
> #ifdef MADV_MERGEABLE
>         madvise(start, size, MADV_MERGEABLE);
> #endif
> }
>
>
>
> Look okay?
>
>
>   

Yes.