linux-kernel - Re: [PATCH 2/7] fs/writeback: bail out if there is no more inodes for IO and queued once

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Date: Thu, 08 Feb 2024 11:21:00 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Kemeng Shi <shikemeng@...weicloud.com>, viro@...iv.linux.org.uk, 
	brauner@...nel.org, jack@...e.cz
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] fs/writeback: bail out if there is no more inodes
 for IO and queued once

On Fri, 2024-02-09 at 01:20 +0800, Kemeng Shi wrote:
> For case there is no more inodes for IO in io list from last wb_writeback,
> We may bail out early even there is inode in dirty list should be written
> back. Only bail out when we queued once to avoid missing dirtied inode.
> 
> This is from code reading...
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> ---
>  fs/fs-writeback.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index a9a918972719..edb0cff51673 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -2086,6 +2086,7 @@ static long wb_writeback(struct bdi_writeback *wb,
>  	struct inode *inode;
>  	long progress;
>  	struct blk_plug plug;
> +	bool queued = false;
>  
>  	if (work->for_kupdate)
>  		filter_expired_io(wb);
> @@ -2131,8 +2132,10 @@ static long wb_writeback(struct bdi_writeback *wb,
>  			dirtied_before = jiffies;
>  
>  		trace_writeback_start(wb, work);
> -		if (list_empty(&wb->b_io))
> +		if (list_empty(&wb->b_io)) {
>  			queue_io(wb, work, dirtied_before);
> +			queued = true;
> +		}
>  		if (work->sb)
>  			progress = writeback_sb_inodes(work->sb, wb, work);
>  		else
> @@ -2155,7 +2158,7 @@ static long wb_writeback(struct bdi_writeback *wb,
>  		/*
>  		 * No more inodes for IO, bail
>  		 */
> -		if (list_empty(&wb->b_more_io)) {
> +		if (list_empty(&wb->b_more_io) && queued) {

Wonder if we can simply do
		if (list_empty(&wb->b_more_io) && list_empty(&wb->b_io)) {

if the intention is to not bail if there are still inodes to be be flushed.

Tim

>  			spin_unlock(&wb->list_lock);
>  			break;
>  		}