[PATCH 8/9] spaceman/defrag: readahead for better performance

[Wengang Wang <wen.gang.wang@xxxxxxxxxx>]

Reading ahead take less lock on file compared to "unshare" the file via ioctl.
Do readahead when defrag sleeps for better defrag performace and thus more
file IO time.

Signed-off-by: Wengang Wang <wen.gang.wang@xxxxxxxxxx>
---
 spaceman/defrag.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/spaceman/defrag.c b/spaceman/defrag.c
index 415fe9c2..ab8508bb 100644
--- a/spaceman/defrag.c
+++ b/spaceman/defrag.c
@@ -331,6 +331,18 @@ defrag_fs_limit_hit(int fd)
 }
 
 static bool g_enable_first_ext_share = true;
+static bool g_readahead = false;
+
+static void defrag_readahead(int defrag_fd, off64_t offset, size_t count)
+{
+	if (!g_readahead || g_idle_time <= 0)
+		return;
+
+	if (readahead(defrag_fd, offset, count) < 0) {
+		fprintf(stderr, "readahead failed: %s, errno=%d\n",
+			strerror(errno), errno);
+	}
+}
 
 static int
 defrag_get_first_real_ext(int fd, struct getbmapx *mapx)
@@ -578,6 +590,8 @@ defrag_xfs_defrag(char *file_path) {
 
 		/* checks for EoF and fix up clone */
 		stop = defrag_clone_eof(&clone);
+		defrag_readahead(defrag_fd, seg_off, seg_size);
+
 		if (sleep_time_us > 0)
 			usleep(sleep_time_us);
 
@@ -698,6 +712,7 @@ static void defrag_help(void)
 " -i idle_time       -- time in ms to be idle between segments, 250ms by default\n"
 " -n                 -- disable the \"share first extent\" featue, it's\n"
 "                       enabled by default to speed up\n"
+" -a                 -- do readahead to speed up defrag, disabled by default\n"
 	));
 }
 
@@ -709,7 +724,7 @@ defrag_f(int argc, char **argv)
 	int	i;
 	int	c;
 
-	while ((c = getopt(argc, argv, "s:f:ni")) != EOF) {
+	while ((c = getopt(argc, argv, "s:f:nia")) != EOF) {
 		switch(c) {
 		case 's':
 			g_segment_size_lmt = atoi(optarg) * 1024 * 1024 / 512;
@@ -731,6 +746,10 @@ defrag_f(int argc, char **argv)
 			g_idle_time = atoi(optarg) * 1000;
 			break;
 
+		case 'a':
+			g_readahead = true;
+			break;
+
 		default:
 			command_usage(&defrag_cmd);
 			return 1;
-- 
2.39.3 (Apple Git-146)