Subject: Re: [PATCH 5/6] fs-writeback: move nr_pages == 0 logic to one
 location
To: Jan Kara <jack@suse.cz>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, hannes@cmpxchg.org, clm@fb.com
References: <1505850787-18311-1-git-send-email-axboe@kernel.dk>
 <1505850787-18311-6-git-send-email-axboe@kernel.dk>
 <20170920144159.GF11106@quack2.suse.cz>
 <33ba51dc-cb93-ad8c-d973-41ac12cb9e90@kernel.dk>
 <20170920153627.GI11106@quack2.suse.cz>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <7c7de06e-0621-b121-917a-7abbd0e676d7@kernel.dk>
Date: Wed, 20 Sep 2017 09:40:18 -0600
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On 09/20/2017 09:36 AM, Jan Kara wrote:
> On Wed 20-09-17 09:05:51, Jens Axboe wrote:
>> 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@kernel.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().
> 
> Good point and fully agreed. So you can add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>

Thanks Jan, added. I just sent out the new version, mainly because the
removal or 'nr_pages' changes the later patches a bit. All for the
better, in my opinion.

-- 
Jens Axboe