Re: [Qemu-devel] [PATCH] qemu_vmalloc: align properly for transparent hugepages and KVM

[Anthony Liguori <anthony@codemonkey.ws>]

On 09/05/2011 03:07 AM, Avi Kivity wrote:
> To make good use of transparent hugepages, KVM requires that guest-physical
> and host-virtual addresses share the low 21 bits (as opposed to just the low
> 12 bits normally required).
>
> Adjust qemu_vmalloc() to honor that requirement.  Ignore it for small regions
> to avoid fragmentation.
>
> Signed-off-by: Avi Kivity<avi@redhat.com>

Applied.  Thanks.

Regards,

Anthony Liguori

> ---
>   oslib-posix.c |   14 +++++++++++++-
>   1 files changed, 13 insertions(+), 1 deletions(-)
>
> diff --git a/oslib-posix.c b/oslib-posix.c
> index 196099c..a304fb0 100644
> --- a/oslib-posix.c
> +++ b/oslib-posix.c
> @@ -35,6 +35,13 @@
>   extern int daemon(int, int);
>   #endif
>
> +#if defined(__linux__)&&  defined(__x86_64__)
> +   /* Use 2MB alignment so transparent hugepages can be used by KVM */
> +#  define QEMU_VMALLOC_ALIGN (512 * 4096)
> +#else
> +#  define QEMU_VMALLOC_ALIGN getpagesize()
> +#endif
> +
>   #include "config-host.h"
>   #include "sysemu.h"
>   #include "trace.h"
> @@ -80,7 +87,12 @@ int qemu_daemon(int nochdir, int noclose)
>   void *qemu_vmalloc(size_t size)
>   {
>       void *ptr;
> -    ptr = qemu_memalign(getpagesize(), size);
> +    size_t align = QEMU_VMALLOC_ALIGN;
> +
> +    if (size<  align) {
> +        align = getpagesize();
> +    }
> +    ptr = qemu_memalign(align, size);
>       trace_qemu_vmalloc(size, ptr);
>       return ptr;
>   }