Fengguang Wu <fengguang.wu@xxxxxxxxx> writes:
> Good idea! Yes we can do some estimation and adaptively extend the
> hang timeout for the current writeback_inodes_sb_nr()/sync_inodes_sb()
> call.
>
> Note that it's not going to reliably get rid of false warnings due to
> estimation errors, which could be pretty large and unavoidable on
> change of workload. But still, it would be a net improvement and
> perhaps enough to get rid of most false warnings, while still being
> able to catch livelock or other kind of task hang.
Hi, Fengguang,
I didn't see a patch from you for this, so I went ahead and threw
something together. Let me know what you think of it. I wasn't sure
how to estimate the total I/O that will be issued for syncing out an
entire superblock, though, so I didn't do that part.
Cheers,
Jeff
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8d2fb8c..346f3de 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1291,6 +1291,37 @@ static void wait_sb_inodes(struct super_block *sb)
}
/**
+ * wb_wait_for_completion_nohang - wait for the given work item to
+ * complete, attempting to not falsely trigger the hangcheck timer.
+ * @work: the wb_writeback_work we're waiting on
+ *
+ * Wait for the completion of the given work item. If the hang check
+ * timer is activated, then estimate the amount of time we should spend
+ * waiting for I/O, and wake up often enough to not trigger the timer.
+ * Once we've exceeded the estimated I/O time, wait without a timeout so
+ * that the hangcheck timer will then fire.
+ */
+void wb_wait_for_completion_nohang(struct wb_writeback_work *work)
+{
+ unsigned long hang_check = sysctl_hung_task_timeout_secs;
+ bool completed = false;
+
+ if (hang_check) {
+ /* loop until the time remaining is less than the timer */
+ unsigned long est_io_time_s = work->nr_pages /
+ work->sb->s_bdi->avg_write_bandwidth;
+ while (!completed && est_io_time_s > hang_check) {
+ completed = !!wait_for_completion_timeout(work->done,
+ hang_check * (HZ/2));
+ est_io_time_s -= hang_check / 2;
+ }
+ }
+
+ if (!completed)
+ wait_for_completion(work->done);
+}
+
+/**
* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
* @sb: the superblock
* @nr: the number of pages to write
@@ -1316,7 +1347,7 @@ void writeback_inodes_sb_nr(struct super_block *sb,
WARN_ON(!rwsem_is_locked(&sb->s_umount));
bdi_queue_work(sb->s_bdi, &work);
- wait_for_completion(&done);
+ wb_wait_for_completion_nohang(&work);
}
EXPORT_SYMBOL(writeback_inodes_sb_nr);
--
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