Re: [QEMU PATCH] KVM: Support for page hinting

[Nitesh Narayan Lal]

On 6/4/19 12:41 PM, Alexander Duyck wrote:
> On Mon, Jun 3, 2019 at 10:04 AM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote:
>> Enables QEMU to call madvise on the pages which are reported
>> by the guest kernel.
>>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
>> ---
>>  hw/virtio/trace-events                        |  1 +
>>  hw/virtio/virtio-balloon.c                    | 85 +++++++++++++++++++
>>  include/hw/virtio/virtio-balloon.h            |  2 +-
>>  include/qemu/osdep.h                          |  7 ++
>>  .../standard-headers/linux/virtio_balloon.h   |  1 +
>>  5 files changed, 95 insertions(+), 1 deletion(-)
> <snip>
>
>> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
>> index 840af09cb0..4d632933a9 100644
>> --- a/include/qemu/osdep.h
>> +++ b/include/qemu/osdep.h
>> @@ -360,6 +360,11 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>>  #else
>>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>>  #endif
>> +#ifdef MADV_FREE
>> +#define QEMU_MADV_FREE MADV_FREE
>> +#else
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>> +#endif
> Is there a specific reason for making this default to INVALID instead
> of just using DONTNEED?
No specific reason.
>  I ran into some issues as my host kernel
> didn't have support for MADV_FREE in the exported kernel headers
> apparently so I was getting no effect. It seems like it would be
> better to fall back to doing DONTNEED instead of just disabling the
> functionality all together.
Possibly, I will further look into it.
>>  #elif defined(CONFIG_POSIX_MADVISE)
>>
>> @@ -373,6 +378,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>>  #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
>>  #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
>>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
> Same here. If you already have MADV_DONTNEED you could just use that
> instead of disabling the functionality.
>
>>  #else /* no-op */
>>
>> @@ -386,6 +392,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>>  #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
>>  #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
>>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>>
>>  #endif
>>
-- 
Regards
Nitesh

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