Re: [f2fs-dev] [PATCH 03/14] f2fs: support regular file buffered writes

[Nanzhe Zhao]

On Thu, 27 Aug 2026 16:56:53 +0800, Chao Yu wrote:
> +	/* Wait for pending drops back to bias which indicates all bio have completed. */
> +	while (READ_ONCE(ffs->read_pages_pending) != 1)
> +		f2fs_io_schedule_timeout(DEFAULT_SCHEDULE_TIMEOUT);
>
> Suspect there will be potential performance issue, as timeout interval
> is large.
>
> Looks hacky.

Thanks for the review.

Maybe we can switch this to an event-driven wait instead:

--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ includes
 	#include <linux/fiemap.h>
+	#include <linux/wait_bit.h>	/* wait_var_event_io / wake_up_var */
 	#include <linux/iomap.h>
@@ f2fs_submit_page_read_sync()
-	/* Wait for pending drops back to bias which indicates all bio have completed. */
-	while (READ_ONCE(ffs->read_pages_pending) != 1)
-		f2fs_io_schedule_timeout(DEFAULT_SCHEDULE_TIMEOUT);
+	/* Wait until all bios have completed (pending drops back to our bias). */
+	wait_var_event_io(&ffs->read_pages_pending,
+			  READ_ONCE(ffs->read_pages_pending) == 1);
@@ f2fs_finish_read_bio()
 			ffs->read_pages_pending -= nr_pages;
 			finished = !ffs->read_pages_pending;
 			spin_unlock_irqrestore(&ffs->state_lock, flags);
+
+			/* Wake f2fs_submit_page_read_sync() waiters (if any). */
+			wake_up_var(&ffs->read_pages_pending);
 		}

However, this requires an extra wake_up_var(&ffs->read_pages_pending)
in f2fs_finish_read_bio(). I'm not sure whether adding an extra
wake-up in the completion callback is a good practice - what do you
think?

Thanks,
Nanzhe