Commit c2dfc5ba authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

oslib: rework anonimous RAM allocation 



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: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0cf33fb6

util/oslib-posix.c

+10 −2
Original line number Diff line number Diff line
@@ -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;