From ac452d097f380b94332e2007d3cbc3bed0c52b72 Mon Sep 17 00:00:00 2001 From: Xiaoguang Wang Date: Thu, 15 Nov 2018 13:47:32 +0800 Subject: [PATCH] alios: jbd2: add proc entry to control whether doing buffer copy-out When jbd2 tries to get write access to one buffer, and if this buffer is under writeback with BH_Shadow flag, jbd2 will wait until this buffer has been written to disk, but sometimes the time taken to wait may be much long, especially disk capacity is almost full. Here add a proc entry "force-copy", if its value is not zero, jbd2 will always do meta buffer copy-cout, then we can eliminate the unnecessary wating time here, and reduce long tail latency for buffered-write. I construct such test case below: $cat offline.fio ; fio-rand-RW.job for fiotest [global] name=fio-rand-RW filename=fio-rand-RW rw=randrw rwmixread=60 rwmixwrite=40 bs=4K direct=0 numjobs=4 time_based=1 runtime=900 [file1] size=60G ioengine=sync iodepth=16 $cat online.fio ; fio-seq-write.job for fiotest [global] name=fio-seq-write filename=fio-seq-write rw=write bs=256K direct=0 numjobs=1 time_based=1 runtime=60 [file1] rate=50m size=10G ioengine=sync iodepth=16 With this patch: $cat /proc/fs/jbd2/sda5-8/force_copy 0 online fio almost always get such long tail latency: Jobs: 1 (f=1), 0B/s-0B/s: [W(1)][100.0%][w=50.0MiB/s][w=200 IOPS][eta 00m:00s] file1: (groupid=0, jobs=1): err= 0: pid=17855: Thu Nov 15 09:45:57 2018 write: IOPS=200, BW=50.0MiB/s (52.4MB/s)(3000MiB/60001msec) clat (usec): min=135, max=4086.6k, avg=867.21, stdev=50338.22 lat (usec): min=139, max=4086.6k, avg=871.16, stdev=50338.22 clat percentiles (usec): | 1.00th=[ 141], 5.00th=[ 143], 10.00th=[ 145], | 20.00th=[ 147], 30.00th=[ 147], 40.00th=[ 149], | 50.00th=[ 149], 60.00th=[ 151], 70.00th=[ 153], | 80.00th=[ 155], 90.00th=[ 159], 95.00th=[ 163], | 99.00th=[ 255], 99.50th=[ 273], 99.90th=[ 429], | 99.95th=[ 441], 99.99th=[3640656] $cat /proc/fs/jbd2/sda5-8/force_copy 1 online fio latency is much better. Jobs: 1 (f=1), 0B/s-0B/s: [W(1)][100.0%][w=50.0MiB/s][w=200 IOPS][eta 00m:00s] file1: (groupid=0, jobs=1): err= 0: pid=8084: Thu Nov 15 09:31:15 2018 write: IOPS=200, BW=50.0MiB/s (52.4MB/s)(3000MiB/60001msec) clat (usec): min=137, max=545, avg=151.35, stdev=16.22 lat (usec): min=140, max=548, avg=155.31, stdev=16.65 clat percentiles (usec): | 1.00th=[ 143], 5.00th=[ 145], 10.00th=[ 145], 20.00th=[ 147], | 30.00th=[ 147], 40.00th=[ 147], 50.00th=[ 149], 60.00th=[ 149], | 70.00th=[ 151], 80.00th=[ 155], 90.00th=[ 157], 95.00th=[ 161], | 99.00th=[ 239], 99.50th=[ 269], 99.90th=[ 420], 99.95th=[ 429], | 99.99th=[ 537] As to the cost: because we'll always need to copy meta buffer, will consume minor cpu time and some memory(at most 32MB for 128MB journal size). Signed-off-by: Xiaoguang Wang Reviewed-by: Liu Bo Signed-off-by: Joseph Qi Acked-by: Caspar Zhang --- fs/jbd2/journal.c | 58 ++++++++++++++++++++++++++++++++++++++++++++ include/linux/jbd2.h | 5 ++++ 2 files changed, 63 insertions(+) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index fc6f36a4d43f..440276af11b4 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -472,6 +472,9 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction, } kunmap_atomic(mapped_data); + /* force copy-out */ + if (need_copy_out == 0 && journal->j_force_copy) + need_copy_out = 1; /* * Do we need to do a data copy? */ @@ -1244,6 +1247,58 @@ static const struct file_operations jbd2_seq_stats_fops = { .release = jbd2_seq_stats_release, }; +static int jbd2_seq_force_copy_show(struct seq_file *m, void *v) +{ + journal_t *journal = m->private; + + seq_printf(m, "%u\n", journal->j_force_copy); + return 0; +} + +static int jbd2_seq_force_copy_open(struct inode *inode, struct file *filp) +{ + journal_t *journal = PDE_DATA(inode); + + return single_open(filp, jbd2_seq_force_copy_show, journal); +} + +/* Worst case buffer size needed for holding an integer. */ +#define PROC_NUMBUF 13 + +static ssize_t jbd2_seq_force_copy_write(struct file *file, + const char __user *buf, size_t count, loff_t *offset) +{ + struct inode *inode = file_inode(file); + journal_t *journal = PDE_DATA(inode); + char buffer[PROC_NUMBUF]; + unsigned int force_copy; + int err; + + memset(buffer, 0, sizeof(buffer)); + if (count > sizeof(buffer) - 1) + count = sizeof(buffer) - 1; + if (copy_from_user(buffer, buf, count)) { + err = -EFAULT; + goto out; + } + + err = kstrtouint(strstrip(buffer), 0, &force_copy); + if (err) + goto out; + journal->j_force_copy = force_copy; +out: + return err < 0 ? err : count; +} + +static const struct file_operations jbd2_seq_force_copy_fops = { + .owner = THIS_MODULE, + .open = jbd2_seq_force_copy_open, + .read = seq_read, + .write = jbd2_seq_force_copy_write, + .llseek = seq_lseek, + .release = single_release, +}; + static struct proc_dir_entry *proc_jbd2_stats; static void jbd2_stats_proc_init(journal_t *journal) @@ -1252,6 +1307,8 @@ static void jbd2_stats_proc_init(journal_t *journal) if (journal->j_proc_entry) { proc_create_data("info", S_IRUGO, journal->j_proc_entry, &jbd2_seq_info_fops, journal); + proc_create_data("force_copy", 0644, journal->j_proc_entry, + &jbd2_seq_force_copy_fops, journal); proc_create_data("stats", S_IRUGO, journal->j_proc_entry, &jbd2_seq_stats_fops, journal); } @@ -1260,6 +1317,7 @@ static void jbd2_stats_proc_init(journal_t *journal) static void jbd2_stats_proc_exit(journal_t *journal) { remove_proc_entry("info", journal->j_proc_entry); + remove_proc_entry("force_copy", journal->j_proc_entry); remove_proc_entry("stats", journal->j_proc_entry); remove_proc_entry(journal->j_devname, proc_jbd2_stats); } diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h index ffe75e2f25df..d0bfa04e5af0 100644 --- a/include/linux/jbd2.h +++ b/include/linux/jbd2.h @@ -1140,6 +1140,11 @@ struct journal_s */ struct transaction_stats_s j_stats; + /** + * @j_force_copy: if not zero, force to do buffer copy-out. + */ + unsigned int j_force_copy; + /** * @j_failed_commit: Failed journal commit ID. */ -- GitLab