Re: [Qemu-devel] [PATCH] split memory allocation

[Anthony Liguori <anthony@codemonkey.ws>]

Aurelien Jarno wrote:
> Glauber Costa a écrit :
>   
>> Right now, kvm keeps the memory allocation split, so we can
>> handle different areas in different ways. This schema works with qemu
>> too, so it appears to be the common ground.
>>
>> This patch proposes using this common ground for everyone, by spliting
>> raw qemu.
>>
>> Signed-off-by: Glauber Costa <glommer@redhat.com>
>> ---
>>  hw/pc.c |   16 ++++++++++++----
>>  1 files changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/pc.c b/hw/pc.c
>> index 435c7d4..d6084ee 100644
>> --- a/hw/pc.c
>> +++ b/hw/pc.c
>> @@ -777,16 +777,24 @@ static void pc_init1(ram_addr_t ram_size, int vga_ram_size,
>>      vmport_init();
>>  
>>      /* allocate RAM */
>> -    ram_addr = qemu_ram_alloc(ram_size);
>> -    cpu_register_physical_memory(0, below_4g_mem_size, ram_addr);
>> +    ram_addr = qemu_ram_alloc(0xa0000);
>> +    cpu_register_physical_memory(0, 0xa0000, ram_addr);
>> +
>> +    ram_addr = qemu_ram_alloc(0x100000 - 0xa0000);   /* hole */
>>     
>
> What the point of allocating RAM for the memory hole if it is not mapped?
>   

If you don't, you violate the phys_ram_base + PA assumption for all of 
memory.  No code should rely on this but practically speaking, there is 
still some code in QEMU that does.

Since the RAM is never touched, it doesn't actually impact the RSS size 
so it's not all that important.

Regards,

Anthony Liguori