[PATCH v2 proxmox 2/6] io: request zeroed memory instead of manually clearing it

[Robert Obkircher <r.obkircher@proxmox.com>]

A quick comparison using cargo bench showed no notable differences in
release mode, but in debug mode 1 GiB allocations by themselves got
43879 times faster. This is because the standard library continued to
call alloc_zeroed, matching release mode, while the previous version
actually had to touch the memory. With an additional .fill(1) the
speedup shrank to around 1.09x.

Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
---
 proxmox-io/src/boxed.rs   | 7 ++-----
 proxmox-io/src/vec/mod.rs | 6 +-----
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/proxmox-io/src/boxed.rs b/proxmox-io/src/boxed.rs
index 7af51cfc..fb67bfd7 100644
--- a/proxmox-io/src/boxed.rs
+++ b/proxmox-io/src/boxed.rs
@@ -12,9 +12,6 @@ pub fn uninitialized(len: usize) -> Box<[u8]> {
 
 /// Zero-initialized bytes, meant for large sizes to avoid busting the stack.
 pub fn zeroed(len: usize) -> Box<[u8]> {
-    let mut bytes = uninitialized(len);
-    unsafe {
-        std::ptr::write_bytes(bytes.as_mut_ptr(), 0, bytes.len());
-    }
-    bytes
+    // vec! guarantees not to over-allocate, so shrink_to_fit inside into_boxed_slice does nothing
+    vec![0; len].into_boxed_slice()
 }
diff --git a/proxmox-io/src/vec/mod.rs b/proxmox-io/src/vec/mod.rs
index b68fc750..7fe106e8 100644
--- a/proxmox-io/src/vec/mod.rs
+++ b/proxmox-io/src/vec/mod.rs
@@ -69,11 +69,7 @@ pub fn clear(data: &mut [u8]) {
 /// Create a newly allocated, zero initialized byte vector.
 #[inline]
 pub fn zeroed(len: usize) -> Vec<u8> {
-    unsafe {
-        let mut out = uninitialized(len);
-        clear(&mut out);
-        out
-    }
+    vec![0; len]
 }
 
 /// Create a newly allocated byte vector of a specific size with "undefined" content.
-- 
2.47.3