On Wed, Jul 30, 2014 at 9:51 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> Il 30/07/2014 13:39, Ming Lei ha scritto:
>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>> index a60104c..943e72f 100644
>> --- a/include/hw/virtio/virtio.h
>> +++ b/include/hw/virtio/virtio.h
>> @@ -84,12 +84,17 @@ typedef struct VirtQueue VirtQueue;
>> typedef struct VirtQueueElement
>> {
>> unsigned int index;
>> + unsigned int num;
>> unsigned int out_num;
>> unsigned int in_num;
>> - hwaddr in_addr[VIRTQUEUE_MAX_SIZE];
>> - hwaddr out_addr[VIRTQUEUE_MAX_SIZE];
>> - struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
>> - struct iovec out_sg[VIRTQUEUE_MAX_SIZE];
>> +
>> + hwaddr *in_addr;
>> + hwaddr *out_addr;
>> + struct iovec *in_sg;
>> + struct iovec *out_sg;
>> +
>> + hwaddr addr[VIRTQUEUE_MAX_SIZE];
>> + struct iovec sg[VIRTQUEUE_MAX_SIZE];
>> } VirtQueueElement;
>>
>> #define VIRTIO_PCI_QUEUE_MAX 64
>> --
>
> since addr and sg aren't used directly, allocate them flexibly like
>
> char *p;
> VirtQueueElement *elem;
> total_size = ROUND_UP(sizeof(struct VirtQueueElement),
> __alignof__(elem->addr[0]);
> addr_offset = total_size;
> total_size = ROUND_UP(total_size + num * sizeof(elem->addr[0]),
> __alignof__(elem->sg[0]));
> sg_offset = total_size;
> total_size += num * sizeof(elem->sg[0]);
>
> elem = p = g_slice_alloc(total_size);
> elem->size = total_size;
> elem->in_addr = p + addr_offset;
> elem->out_addr = elem->in_addr + in_num;
> elem->in_sg = p + sg_offset;
> elem->out_sg = elem->in_sg + in_num;
>
> ...
>
> g_slice_free1(elem->size, elem);
>
> The small size will help glib do slab-style allocation and should remove
> the need for an object pool.
Yes, that should be correct way to do, but can't avoid big chunk allocation
completely because 'num' is a bit big.
Also this kind of change requires almost all users of elem to be changed,
that need lots of work.
That is why I choose to take the simple approach to ease memory
preallocation for obj pool.
Thanks,
