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qemu_vmalloc: align properly for transparent hugepages and KVM 

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>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Avi Kivity 2011-09-05 11:07:05 +03:00 committed by Anthony Liguori
parent df00bed0fa
commit 36b586284e
1 changed files with 13 additions and 1 deletions
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14
oslib-posix.c
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@ -35,6 +35,13 @@
extern int daemon(int, int); extern int daemon(int, int);
#endif #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 "config-host.h"
#include "sysemu.h" #include "sysemu.h"
#include "trace.h" #include "trace.h"
@ -80,7 +87,12 @@ void *qemu_memalign(size_t alignment, size_t size)
void *qemu_vmalloc(size_t size) void *qemu_vmalloc(size_t size)
{ {
void *ptr; 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); trace_qemu_vmalloc(size, ptr);
return ptr; return ptr;
} }