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oslib: rework anonimous RAM allocation

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At the moment we first allocate RAM, sometimes more than necessary for
alignment reasons.  We then free the extra RAM.

Rework this to avoid the temporary allocation: reserve the
range by mapping it with PROT_NONE, then use just the
necessary range with MAP_FIXED.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2015-09-10 16:36:51 +03:00
parent 0cf33fb6b4
commit c2dfc5ba3f
1 changed files with 10 additions and 2 deletions
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12
util/oslib-posix.c
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@ -129,9 +129,9 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment)
{
size_t align = QEMU_VMALLOC_ALIGN;
size_t total = size + align - getpagesize();
void *ptr = mmap(0, total, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
void *ptr1;
if (ptr == MAP_FAILED) {
return NULL;
@ -140,6 +140,14 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment)
if (alignment) {
*alignment = align;
}
ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (ptr1 == MAP_FAILED) {
munmap(ptr, total);
return NULL;
}
ptr += offset;
total -= offset;