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

[Kemeng Shi <shikemeng@huaweicloud.com>]

on 2/9/2024 3:21 AM, Tim Chen wrote:
> 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@huaweicloud.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.
I suppose not as there may be inodes in wb->b_dirty should be flushed.
For case that there is a inode in wb->b_io which is not flushed in last
wb_writeback and there are a lot of inodes in wb->dirty, the next background
flush is supposed to make dirty pages under threshold however only the inode
in wb->b_io is flushed.
> 
> Tim
> 
>>  			spin_unlock(&wb->list_lock);
>>  			break;
>>  		}
>