Re: [PATCH 7/8] btrfs: be more explicit about allowed flush states

[Nikolay Borisov <nborisov@suse.com>]

On 26.11.18 г. 14:41 ч., Nikolay Borisov wrote:
> 
> 
> On 21.11.18 г. 21:03 ч., Josef Bacik wrote:
>> For FLUSH_LIMIT flushers we really can only allocate chunks and flush
>> delayed inode items, everything else is problematic.  I added a bunch of
>> new states and it lead to weirdness in the FLUSH_LIMIT case because I
>> forgot about how it worked.  So instead explicitly declare the states
>> that are ok for flushing with FLUSH_LIMIT and use that for our state
>> machine.  Then as we add new things that are safe we can just add them
>> to this list.
> 
> 
> Code-wise it's ok but the changelog needs rewording. At the very least
> explain the weirdness. Also in the last sentence the word 'thing' is
> better substituted with "flush states".

Case in point, you yourself mention that you have forgotten how the
FLUSH_LIMIT case works. That's why we need good changelogs so that those
details can be quickly worked out from reading the changelog.


> 
>>
>> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
>> ---
>>  fs/btrfs/extent-tree.c | 21 ++++++++++-----------
>>  1 file changed, 10 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 0e9ba77e5316..e31980d451c2 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -5112,12 +5112,18 @@ void btrfs_init_async_reclaim_work(struct work_struct *work)
>>  	INIT_WORK(work, btrfs_async_reclaim_metadata_space);
>>  }
>>  
>> +static const enum btrfs_flush_state priority_flush_states[] = {
>> +	FLUSH_DELAYED_ITEMS_NR,
>> +	FLUSH_DELAYED_ITEMS,
>> +	ALLOC_CHUNK,
>> +};
>> +
>>  static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
>>  					    struct btrfs_space_info *space_info,
>>  					    struct reserve_ticket *ticket)
>>  {
>>  	u64 to_reclaim;
>> -	int flush_state = FLUSH_DELAYED_ITEMS_NR;
>> +	int flush_state = 0;
>>  
>>  	spin_lock(&space_info->lock);
>>  	to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info, space_info,
>> @@ -5129,7 +5135,8 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
>>  	spin_unlock(&space_info->lock);
>>  
>>  	do {
>> -		flush_space(fs_info, space_info, to_reclaim, flush_state);
>> +		flush_space(fs_info, space_info, to_reclaim,
>> +			    priority_flush_states[flush_state]);
>>  		flush_state++;
>>  		spin_lock(&space_info->lock);
>>  		if (ticket->bytes == 0) {
>> @@ -5137,15 +5144,7 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
>>  			return;
>>  		}
>>  		spin_unlock(&space_info->lock);
>> -
>> -		/*
>> -		 * Priority flushers can't wait on delalloc without
>> -		 * deadlocking.
>> -		 */
>> -		if (flush_state == FLUSH_DELALLOC ||
>> -		    flush_state == FLUSH_DELALLOC_WAIT)
>> -			flush_state = ALLOC_CHUNK;
>> -	} while (flush_state < COMMIT_TRANS);
>> +	} while (flush_state < ARRAY_SIZE(priority_flush_states));
>>  }
>>  
>>  static int wait_reserve_ticket(struct btrfs_fs_info *fs_info,
>>
>