On Tue, Jul 09, 2024 at 12:10:27PM -0700, Wengang Wang wrote:
> 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);
Why is it worth reporting if readahead fails? Won't the unshare also
fail? I'm also wondering why we wouldn't want readahead all the time?
--D
> + }
> +}
>
> 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)
>
>
