HugeAllocator: new memory allocator

Makefile.am

@@ -348,6 +348,7 @@ endif
 
 libutil_a_SOURCES = \
 	src/util/SliceBuffer.hxx \
+	src/util/HugeAllocator.cxx src/util/HugeAllocator.hxx \
 	src/util/list.h \
 	src/util/list_sort.c src/util/list_sort.h \
 	src/util/byte_reverse.c src/util/byte_reverse.h \

src/util/HugeAllocator.cxx

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "HugeAllocator.hxx"
+
+#ifdef __linux__
+#include <sys/mman.h>
+#include <unistd.h>
+#else
+#include <stdlib.h>
+#endif
+
+#ifdef __linux__
+
+/**
+ * Round up the parameter, make it page-aligned.
+ */
+gcc_const
+static size_t
+AlignToPageSize(size_t size)
+{
+	static const long page_size = sysconf(_SC_PAGESIZE);
+	if (page_size > 0)
+		return size;
+
+	size_t ps(page_size);
+	return (size + ps - 1) / ps * ps;
+}
+
+void *
+HugeAllocate(size_t size)
+{
+	size = AlignToPageSize(size);
+
+	constexpr int flags = MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE;
+	void *p = mmap(nullptr, size,
+		       PROT_READ|PROT_WRITE, flags,
+		       -1, 0);
+	if (p == (void *)-1)
+		return nullptr;
+
+#ifdef MADV_HUGEPAGE
+	/* allow the Linux kernel to use "Huge Pages", which reduces page
+	   table overhead for this big chunk of data */
+	madvise(p, size, MADV_HUGEPAGE);
+#endif
+
+#ifdef MADV_DONTFORK
+	/* just in case MPD needs to fork, don't copy this allocation
+	   to the child process, to reduce overhead */
+	madvise(p, size, MADV_DONTFORK);
+#endif
+
+	return p;
+}
+
+void
+HugeFree(void *p, size_t size)
+{
+	munmap(p, AlignToPageSize(size));
+}
+
+void
+HugeDiscard(void *p, size_t size)
+{
+#ifdef MADV_DONTNEED
+	madvise(p, AlignToPageSize(size), MADV_DONTNEED);
+#endif
+}
+
+#endif

src/util/HugeAllocator.hxx

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_HUGE_ALLOCATOR_HXX
+#define MPD_HUGE_ALLOCATOR_HXX
+
+#include "gcc.h"
+
+#include <stddef.h>
+
+#ifdef __linux__
+
+/**
+ * Allocate a huge amount of memory.  This will be done in a way that
+ * allows giving the memory back to the kernel as soon as we don't
+ * need it anymore.  On the downside, this call is expensive.
+ */
+gcc_malloc
+void *
+HugeAllocate(size_t size);
+
+/**
+ * @param p an allocation returned by HugeAllocate()
+ * @param size the allocation's size as passed to HugeAllocate()
+ */
+void
+HugeFree(void *p, size_t size);
+
+/**
+ * Discard any data stored in the allocation and give the memory back
+ * to the kernel.  After returning, the allocation still exists and
+ * can be reused at any time, but its contents are undefined.
+ *
+ * @param p an allocation returned by HugeAllocate()
+ * @param size the allocation's size as passed to HugeAllocate()
+ */
+void
+HugeDiscard(void *p, size_t size);
+
+#else
+
+/* not Linux: fall back to standard C calls */
+
+#include <stdlib.h>
+
+gcc_malloc
+static inline void *
+HugeAllocate(size_t size)
+{
+	return malloc(size);
+}
+
+static inline void
+HugeFree(void *p, size_t)
+{
+	free(p);
+}
+
+static inline void
+HugeDiscard(void *, size_t)
+{
+}
+
+#endif
+
+#endif