linux-kernel - Re: [PATCH 5/6] fs-writeback: move nr

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Date:   Wed, 20 Sep 2017 09:05:51 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, hannes@...xchg.org, clm@...com
Subject: Re: [PATCH 5/6] fs-writeback: move nr_pages == 0 logic to one
 location

On 09/20/2017 08:41 AM, Jan Kara wrote:
> On Tue 19-09-17 13:53:06, Jens Axboe wrote:
>> Now that we have no external callers of wb_start_writeback(),
>> we can move the nr_pages == 0 logic into that function.
>>
>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> 
> ...
> 
>> +static unsigned long get_nr_dirty_pages(void)
>> +{
>> +	return global_node_page_state(NR_FILE_DIRTY) +
>> +		global_node_page_state(NR_UNSTABLE_NFS) +
>> +		get_nr_dirty_inodes();
>> +}
>> +
>>  static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
>>  			       bool range_cyclic, enum wb_reason reason)
>>  {
>> @@ -942,6 +953,12 @@ static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
>>  		return;
>>  
>>  	/*
>> +	 * If someone asked for zero pages, we write out the WORLD
>> +	 */
>> +	if (!nr_pages)
>> +		nr_pages = get_nr_dirty_pages();
>> +
> 
> So for 'wb' we have a better estimate of the amount we should write - use
> wb_stat_sum(wb, WB_RECLAIMABLE) statistics - that is essentially dirty +
> unstable_nfs broken down to bdi_writeback.

I don't mind making that change, but I think that should be a separate
patch. We're using get_nr_dirty_pages() in existing locations where
we have the 'wb', like in wb_check_old_data_flush().

-- 
Jens Axboe