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[Qemu-devel] [PATCH repost 1/4] oslib: rework anonimous RAM allocation
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] [PATCH repost 1/4] oslib: rework anonimous RAM allocation |
Date: |
Sun, 27 Sep 2015 13:14:30 +0300 |
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 <address@hidden>
---
util/oslib-posix.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 3ae4987..27972d4 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -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;
--
MST