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Re: [Qemu-devel] [PATCH v2 4/6] hostmem: hostmem listener pin RAM-Device


From: liu ping fan
Subject: Re: [Qemu-devel] [PATCH v2 4/6] hostmem: hostmem listener pin RAM-Device by refcnt
Date: Mon, 6 May 2013 09:45:28 +0800

On Fri, May 3, 2013 at 5:35 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Fri, May 03, 2013 at 10:45:20AM +0800, Liu Ping Fan wrote:
>> From: Liu Ping Fan <address@hidden>
>>
>> With ref()/unref() interface of MemoryRegion, we can pin RAM-Device
>> when using its memory, and release it when done.
>>
>> Signed-off-by: Liu Ping Fan <address@hidden>
>> ---
>>  hw/virtio/dataplane/hostmem.c         |   44 
>> +++++++++++++++++++++++++++-----
>>  hw/virtio/dataplane/vring.c           |    8 +++---
>>  include/hw/virtio/dataplane/hostmem.h |    4 ++-
>>  3 files changed, 44 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/virtio/dataplane/hostmem.c b/hw/virtio/dataplane/hostmem.c
>> index 1fd3e06..0e28dfc 100644
>> --- a/hw/virtio/dataplane/hostmem.c
>> +++ b/hw/virtio/dataplane/hostmem.c
>> @@ -42,18 +42,28 @@ static void hostmem_ref(HostMem *hostmem)
>>
>>  static void hostmem_unref(HostMem *hostmem)
>>  {
>> -    int t;
>> +    int i, t;
>> +    HostMemRegion *hmr;
>>
>>      t = __sync_sub_and_fetch(&hostmem->ref, 1);
>>      assert(t >= 0);
>>      if (!t) {
>> +        for (i = 0; i < hostmem->num_current_regions; i++) {
>> +            hmr = &hostmem->current_regions[i];
>> +            /* Fix me, when memory hotunplug implement
>> +             * assert(hmr->mr_ops->unref)
>> +             */
>> +            if (hmr->mr->ops && hmr->mr->ops->unref) {
>> +                hmr->mr->ops->unref();
>> +            }
>
> This patch should use memory_region_ref()/unref() which you introduced
> in the previous patch instead of open-coding this.
>
Yes, reasonable.
>> @@ -158,6 +176,18 @@ static void 
>> hostmem_listener_append_region(MemoryListener *listener,
>>      hostmem_append_new_region(as_mem->next_hostmem, section);
>>  }
>>
>> +static void hostmem_listener_append_region(MemoryListener *listener,
>> +                                           MemoryRegionSection *section)
>> +{
>> +    hostmem_listener_nop_region(listener, section);
>> +    /* Fix me, when memory hotunplug implement
>> +     * assert(section->mr->ops->ref)
>> +     */
>> +    if (section->mr->ops && section->mr->ops->ref) {
>> +        section->mr->ops->ref();
>> +    }
>> +}
>
> Why does append increment the refcount while nop does not?
>
> It seems that we always need to increment the memory region refcount
> since we're building a completely new hostmem.  The refcount ownership
> is not passed from the current hostmen to the next hostmem, all memory
> regions are released in hostmem_unref().

Yes, you are right.  Will fix it.

Thanks,
Pingfan



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