Subject: [PATCH v2 4/5] Move the reusable parts of memory pool into its own file

From: Jameson Miller <[email-masked]>
Date: Fri, 23 Mar 2018 10:44:07 -0400

This moves the reusable parts of the memory pool logic used by
fast-import.c into its own file for use by other components.

Signed-off-by: Jameson Miller <[email-masked]>
---
 Makefile      |   1 +
 fast-import.c | 118 +---------------------------------------------------------
 mem-pool.c    | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++
 mem-pool.h    |  34 +++++++++++++++++
 4 files changed, 139 insertions(+), 117 deletions(-)
 create mode 100644 mem-pool.c
 create mode 100644 mem-pool.h

diff --git a/Makefile b/Makefile
index a1d8775adb..1e142b1dd9 100644
--- a/Makefile
+++ b/Makefile
@@ -832,6 +832,7 @@ LIB_OBJS += lockfile.o
 LIB_OBJS += log-tree.o
 LIB_OBJS += mailinfo.o
 LIB_OBJS += mailmap.o
+LIB_OBJS += mem-pool.o
 LIB_OBJS += match-trees.o
 LIB_OBJS += merge.o
 LIB_OBJS += merge-blobs.o
diff --git a/fast-import.c b/fast-import.c
index 519e1cbd7f..36ac5760d6 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -168,6 +168,7 @@ Format of STDIN stream:
 #include "dir.h"
 #include "run-command.h"
 #include "packfile.h"
+#include "mem-pool.h"
 
 #define PACK_ID_BITS 16
 #define MAX_PACK_ID ((1<<PACK_ID_BITS)-1)
@@ -209,26 +210,6 @@ struct last_object {
 	unsigned no_swap : 1;
 };
 
-struct mp_block {
-	struct mp_block *next_block;
-	char *next_free;
-	char *end;
-	uintmax_t space[FLEX_ARRAY]; /* more */
-};
-
-struct mem_pool {
-	struct mp_block *mp_block;
-
-	/*
-	 * The amount of available memory to grow the pool by.
-	 * This size does not include the overhead for the mp_block.
-	 */
-	size_t block_alloc;
-
-	/* The total amount of memory allocated by the pool. */
-	size_t pool_alloc;
-};
-
 struct atom_str {
 	struct atom_str *next_atom;
 	unsigned short str_len;
@@ -646,103 +627,6 @@ static unsigned int hc_str(const char *s, size_t len)
 	return r;
 }
 
-static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool)
-{
-	struct mp_block *p;
-
-	mem_pool->pool_alloc += sizeof(struct mp_block) + mem_pool->block_alloc;
-	p = xmalloc(st_add(sizeof(struct mp_block), mem_pool->block_alloc));
-	p->next_block = mem_pool->mp_block;
-	p->next_free = (char *)p->space;
-	p->end = p->next_free + mem_pool->block_alloc;
-	mem_pool->mp_block = p;
-
-	return p;
-}
-
-/*
- * Allocates a block of memory with a specific size and
- * appends it to the memory pool's list of blocks.
- *
- * This function is used to allocate blocks with sizes
- * different than the default "block_alloc" size for the mem_pool.
- *
- * There are two use cases:
- *  1) The initial block allocation for a memory pool.
- *
- *  2) large" blocks of a specific size, where the entire memory block
- *     is going to be used. This means the block will not have any
- *     available memory for future allocations. The block is placed at
- *     the end of the list so that it will be the last block searched
- *     for available space.
- */
-static struct mp_block *mem_pool_alloc_block_with_size(struct mem_pool *mem_pool, size_t block_alloc)
-{
-	struct mp_block *p, *block;
-
-	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
-	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
-
-	block = mem_pool->mp_block;
-	if (block) {
-		while (block->next_block)
-			block = block->next_block;
-
-		block->next_block = p;
-	} else {
-		mem_pool->mp_block = p;
-	}
-
-	p->next_block = NULL;
-	p->next_free = (char *)p->space;
-	p->end = p->next_free + block_alloc;
-
-	return p;
-}
-
-static void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
-{
-	struct mp_block *p;
-	void *r;
-
-	/* round up to a 'uintmax_t' alignment */
-	if (len & (sizeof(uintmax_t) - 1))
-		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
-
-	p = mem_pool->mp_block;
-
-	/*
-	 * In performance profiling, there was a minor perf benefit to
-	 * check for available memory in the head block via the if
-	 * statement, and only going through the loop when needed.
-	 */
-	if (p &&
-	   (p->end - p->next_free < len)) {
-		for (p = p->next_block; p; p = p->next_block)
-			if (p->end - p->next_free >= len)
-				break;
-	}
-
-	if (!p) {
-		if (len >= (mem_pool->block_alloc / 2))
-			p = mem_pool_alloc_block_with_size(mem_pool, len);
-		else
-			p = mem_pool_alloc_block(mem_pool);
-	}
-
-	r = p->next_free;
-	p->next_free += len;
-	return r;
-}
-
-static void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
-{
-	size_t len = st_mult(count, size);
-	void *r = mem_pool_alloc(mem_pool, len);
-	memset(r, 0, len);
-	return r;
-}
-
 static char *pool_strdup(const char *s)
 {
 	size_t len = strlen(s) + 1;
diff --git a/mem-pool.c b/mem-pool.c
new file mode 100644
index 0000000000..992e354e12
--- /dev/null
+++ b/mem-pool.c
@@ -0,0 +1,103 @@
+/*
+ * Memory Pool implementation logic.
+ */
+
+#include "cache.h"
+#include "mem-pool.h"
+
+static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool)
+{
+	struct mp_block *p;
+
+	mem_pool->pool_alloc += sizeof(struct mp_block) + mem_pool->block_alloc;
+	p = xmalloc(st_add(sizeof(struct mp_block), mem_pool->block_alloc));
+	p->next_block = mem_pool->mp_block;
+	p->next_free = (char *)p->space;
+	p->end = p->next_free + mem_pool->block_alloc;
+	mem_pool->mp_block = p;
+
+	return p;
+}
+
+/*
+ * Allocates a block of memory with a specific size and
+ * appends it to the memory pool's list of blocks.
+ *
+ * This function is used to allocate blocks with sizes
+ * different than the default "block_alloc" size for the mem_pool.
+ *
+ * There are two use cases:
+ *  1) The initial block allocation for a memory pool.
+ *
+ *  2) large" blocks of a specific size, where the entire memory block
+ *     is going to be used. This means the block will not have any
+ *     available memory for future allocations. The block is placed at
+ *     the end of the list so that it will be the last block searched
+ *     for available space.
+ */
+static struct mp_block *mem_pool_alloc_block_with_size(struct mem_pool *mem_pool, size_t block_alloc)
+{
+	struct mp_block *p, *block;
+
+	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
+	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));
+
+	block = mem_pool->mp_block;
+	if (block) {
+		while (block->next_block)
+			block = block->next_block;
+
+		block->next_block = p;
+	} else {
+		mem_pool->mp_block = p;
+	}
+
+	p->next_block = NULL;
+	p->next_free = (char *)p->space;
+	p->end = p->next_free + block_alloc;
+
+	return p;
+}
+
+void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
+{
+	struct mp_block *p;
+	void *r;
+
+	/* round up to a 'uintmax_t' alignment */
+	if (len & (sizeof(uintmax_t) - 1))
+		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
+
+	p = mem_pool->mp_block;
+
+	/*
+	 * In performance profiling, there was a minor perf benefit to
+	 * check for available memory in the head block via the if
+	 * statement, and only going through the loop when needed.
+	 */
+	if (p &&
+	   (p->end - p->next_free < len)) {
+		for (p = p->next_block; p; p = p->next_block)
+			if (p->end - p->next_free >= len)
+				break;
+	}
+
+	if (!p) {
+		if (len >= (mem_pool->block_alloc / 2))
+			p = mem_pool_alloc_block_with_size(mem_pool, len);
+		else
+			p = mem_pool_alloc_block(mem_pool);
+	}
+
+	r = p->next_free;
+	p->next_free += len;
+	return r;
+}
+
+void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
+{
+	size_t len = st_mult(count, size);
+	void *r = mem_pool_alloc(mem_pool, len);
+	memset(r, 0, len);
+	return r;
+}
diff --git a/mem-pool.h b/mem-pool.h
new file mode 100644
index 0000000000..829ad58ecf
--- /dev/null
+++ b/mem-pool.h
@@ -0,0 +1,34 @@
+#ifndef MEM_POOL_H
+#define MEM_POOL_H
+
+struct mp_block {
+	struct mp_block *next_block;
+	char *next_free;
+	char *end;
+	uintmax_t space[FLEX_ARRAY]; /* more */
+};
+
+struct mem_pool {
+	struct mp_block *mp_block;
+
+	/*
+	 * The amount of available memory to grow the pool by.
+	 * This size does not include the overhead for the mp_block.
+	 */
+	size_t block_alloc;
+
+	/* The total amount of memory allocated by the pool. */
+	size_t pool_alloc;
+};
+
+/*
+ * Alloc memory from the mem_pool.
+ */
+void *mem_pool_alloc(struct mem_pool *pool, size_t len);
+
+/*
+ * Allocate and zero memory from the memory pool.
+ */
+void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
+
+#endif
-- 
2.14.3