Add dynamic buffers to f3write and f3read

The write and read buffers passed to the operating system have
previously been limited to MAX_BUFFER_SIZE.  This commit makes
them dynamically sized in order to reach maximum writing and
reading speeds.

See details on issue #188.

f3read.c

@@ -191,15 +191,16 @@ static ssize_t read_all(int fd, char *buf, size_t count)
 	return done;
 }
 
-static ssize_t check_chunk(int fd, uint64_t *p_expected_offset,
-	uint64_t chunk_size, struct file_stats *stats)
+static ssize_t check_chunk(struct dynamic_buffer *dbuf, int fd,
+	uint64_t *p_expected_offset, uint64_t chunk_size,
+	struct file_stats *stats)
 {
-	char buf[MAX_BUFFER_SIZE];
+	char *buf = dbuf_get_buf(dbuf, chunk_size);
+	size_t len = dbuf_get_len(dbuf);
 	ssize_t tot_bytes_read = 0;
 
 	while (chunk_size > 0) {
-		size_t turn_size = chunk_size <= MAX_BUFFER_SIZE
-			? chunk_size : MAX_BUFFER_SIZE;
+		size_t turn_size = chunk_size <= len ? chunk_size : len;
 		ssize_t bytes_read = read_all(fd, buf, turn_size);
 
 		if (bytes_read < 0) {
@@ -235,6 +236,7 @@ static void validate_file(const char *path, int number, struct flow *fw,
 	int fd, saved_errno;
 	ssize_t bytes_read;
 	uint64_t expected_offset;
+	struct dynamic_buffer dbuf;
 
 	zero_fstats(stats);
 
@@ -263,11 +265,12 @@ static void validate_file(const char *path, int number, struct flow *fw,
 	/* Help the kernel to help us. */
 	assert(!posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL));
 
+	dbuf_init(&dbuf);
 	saved_errno = 0;
 	expected_offset = (uint64_t)number * GIGABYTES;
 	start_measurement(fw);
 	while (true) {
-		bytes_read = check_chunk(fd, &expected_offset,
+		bytes_read = check_chunk(&dbuf, fd, &expected_offset,
 			get_rem_chunk_size(fw), stats);
 		if (bytes_read == 0)
 			break;
@@ -297,6 +300,7 @@ static void validate_file(const char *path, int number, struct flow *fw,
 	}
 	printf("\n");
 
+	dbuf_free(&dbuf);
 	close(fd);
 	free(full_fn);
 }

f3write.c

@@ -150,13 +150,14 @@ static int write_all(int fd, const char *buf, size_t count)
 	return 0;
 }
 
-static int write_chunk(int fd, size_t chunk_size, uint64_t *poffset)
+static int write_chunk(struct dynamic_buffer *dbuf, int fd, size_t chunk_size,
+	uint64_t *poffset)
 {
-	char buf[MAX_BUFFER_SIZE];
+	char *buf = dbuf_get_buf(dbuf, chunk_size);
+	size_t len = dbuf_get_len(dbuf);
 
 	while (chunk_size > 0) {
-		size_t turn_size = chunk_size <= MAX_BUFFER_SIZE
-			? chunk_size : MAX_BUFFER_SIZE;
+		size_t turn_size = chunk_size <= len ? chunk_size : len;
 		int ret;
 		chunk_size -= turn_size;
 		*poffset = fill_buffer(buf, turn_size, *poffset);
@@ -177,6 +178,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	int fd, saved_errno;
 	size_t remaining;
 	uint64_t offset;
+	struct dynamic_buffer dbuf;
 
 	assert(size > 0);
 	assert(size % fw->block_size == 0);
@@ -198,6 +200,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	assert(fd >= 0);
 
 	/* Write content. */
+	dbuf_init(&dbuf);
 	saved_errno = 0;
 	offset = (uint64_t)number * GIGABYTES;
 	remaining = size;
@@ -206,7 +209,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 		uint64_t write_size = get_rem_chunk_size(fw);
 		if (write_size > remaining)
 			write_size = remaining;
-		saved_errno = write_chunk(fd, write_size, &offset);
+		saved_errno = write_chunk(&dbuf, fd, write_size, &offset);
 		if (saved_errno)
 			break;
 		remaining -= write_size;
@@ -220,6 +223,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 		if (!saved_errno)
 			saved_errno = errno;
 	}
+	dbuf_free(&dbuf);
 	close(fd);
 	free(full_fn);
 

libflow.c

@@ -366,3 +366,45 @@ out:
 	}
 	return ret;
 }
+
+static inline void __dbuf_free(struct dynamic_buffer *dbuf)
+{
+	if (dbuf->buf != dbuf->backup_buf)
+		free(dbuf->buf);
+}
+
+void dbuf_free(struct dynamic_buffer *dbuf)
+{
+	__dbuf_free(dbuf);
+	dbuf->buf = NULL;
+	dbuf->len = 0;
+	dbuf->max_buf = true;
+}
+
+char *dbuf_get_buf(struct dynamic_buffer *dbuf, size_t size)
+{
+	/* If enough buffer, or it's already the largest buffer, return it. */
+	if (size <= dbuf->len || dbuf->max_buf)
+		return dbuf->buf;
+
+	/*
+	 * Allocate a new buffer.
+	 */
+
+	__dbuf_free(dbuf);
+	do {
+		dbuf->buf = malloc(size);
+		if (dbuf->buf != NULL) {
+			dbuf->len = size;
+			return dbuf->buf;
+		} else {
+			dbuf->max_buf = true;
+		}
+		size /= 2;
+	} while (size > sizeof(dbuf->backup_buf));
+
+	/* A larger buffer is not available; failsafe. */
+	dbuf->buf = dbuf->backup_buf;
+	dbuf->len = sizeof(dbuf->backup_buf);
+	return dbuf->buf;
+}

libflow.h

@@ -2,6 +2,7 @@
 #define HEADER_LIBFLOW_H
 
 #include <stdint.h>
+#include <stdbool.h>
 
 struct flow;
 
@@ -90,6 +91,31 @@ static inline uint64_t get_rem_chunk_size(struct flow *fw)
 	return (fw->blocks_per_delay - fw->processed_blocks) * fw->block_size;
 }
 
-#define MAX_BUFFER_SIZE	(1<<21)	/* 2MB */
+struct dynamic_buffer {
+	char   *buf;
+	size_t len;
+	bool   max_buf;
+	char   backup_buf[1 << 21]; /* 2MB */
+};
+
+static inline void dbuf_init(struct dynamic_buffer *dbuf)
+{
+	dbuf->buf = dbuf->backup_buf;
+	dbuf->len = sizeof(dbuf->backup_buf);
+	dbuf->max_buf = false;
+}
+
+void dbuf_free(struct dynamic_buffer *dbuf);
+
+/*
+ * Although the returned buffer may be smaller than @size,
+ * this function never returns NULL.
+ */
+char *dbuf_get_buf(struct dynamic_buffer *dbuf, size_t size);
+
+static inline size_t dbuf_get_len(const struct dynamic_buffer *dbuf)
+{
+	return dbuf->len;
+}
 
 #endif	/* HEADER_LIBFLOW_H */