From 447a86c922801a9d268a121862c5ae5619bc7f91 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Fri, 4 Jan 2013 20:27:29 +0100
Subject: SliceBuffer: lazy initialization
Avoid page faults on MPD startup. This saves a lot of memory for an
idle MPD.
---
src/util/SliceBuffer.hxx | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
(limited to 'src/util')
diff --git a/src/util/SliceBuffer.hxx b/src/util/SliceBuffer.hxx
index 9ddad6b3d..1f5ff873d 100644
--- a/src/util/SliceBuffer.hxx
+++ b/src/util/SliceBuffer.hxx
@@ -47,6 +47,13 @@ class SliceBuffer {
*/
const unsigned n_max;
+ /**
+ * The number of slices that are initialized. This is used to
+ * avoid page faulting on the new allocation, so the kernel
+ * does not need to reserve physical memory pages.
+ */
+ unsigned n_initialized;
+
/**
* The number of slices currently allocated.
*/
@@ -61,15 +68,9 @@ class SliceBuffer {
public:
SliceBuffer(unsigned _count)
- :n_max(_count), n_allocated(0),
- data(g_new(Slice, n_max)), available(data) {
+ :n_max(_count), n_initialized(0), n_allocated(0),
+ data(g_new(Slice, n_max)), available(nullptr) {
assert(n_max > 0);
-
- Slice *const last = data + n_max - 1;
- for (Slice *slice = data; slice != last; ++slice)
- slice->next = slice + 1;
-
- last->next = nullptr;
}
~SliceBuffer() {
@@ -97,12 +98,18 @@ public:
template<typename... Args>
T *Allocate(Args&&... args) {
- assert(n_allocated <= n_max);
+ assert(n_initialized <= n_max);
+ assert(n_allocated <= n_initialized);
if (available == nullptr) {
- /* out of (internal) memory, buffer is full */
- assert(n_allocated == n_max);
- return nullptr;
+ if (n_initialized == n_max) {
+ /* out of (internal) memory, buffer is full */
+ assert(n_allocated == n_max);
+ return nullptr;
+ }
+
+ available = &data[n_initialized++];
+ available->next = nullptr;
}
/* allocate a slice */
@@ -115,8 +122,9 @@ public:
}
void Free(T *value) {
+ assert(n_initialized <= n_max);
assert(n_allocated > 0);
- assert(n_allocated <= n_max);
+ assert(n_allocated <= n_initialized);
Slice *slice = reinterpret_cast<Slice *>(value);
assert(slice >= data && slice < data + n_max);
--
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