> On Jul 9, 2024, at 1:27 PM, Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
>
> 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?
Yes, if readahead failed, later unshare should fail as I think.
I just want to capture error as soon as possible though readahead is not critical.
> I'm also wondering why we wouldn't want readahead all the time?
As per our tests, readahead on NVME doesn’t hehaved better.
So I’d make it an option.
Thanks,
Wengang
>
> --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)
