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

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 9/7/26 21:03, Nanzhe Zhao wrote:
> 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?

Sure, IMO, stability has higher priority, we can tune this later if it
takes much time.

Thanks,

> 
> Thanks,
> Nanzhe



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