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Re: [Qemu-devel] [PATCH] qemu_vmalloc: align properly for transparent hu
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] [PATCH] qemu_vmalloc: align properly for transparent hugepages and KVM |
Date: |
Mon, 05 Sep 2011 12:10:51 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2011-09-05 10:07, 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 <address@hidden>
> ---
> 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 */
Aren't transparent hugepages also available in TCG mode? Then just
remove "by KVM" from subject and comment.
Jan
> +# 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;
> }
--
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