Re: [PATCH] btrfs: Streamline btrfs_delalloc_reserve_metadata initial operations

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On 30.01.2018 16:34, David Sterba wrote:
> On Fri, Jan 12, 2018 at 04:21:05PM +0200, Nikolay Borisov wrote:
>> @@ -6062,19 +6062,19 @@ int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes)
>>  	 * If we have a transaction open (can happen if we call truncate_block
>>  	 * from truncate), then we need FLUSH_LIMIT so we don't deadlock.
>>  	 */
>> +
>>  	if (btrfs_is_free_space_inode(inode)) {
>>  		flush = BTRFS_RESERVE_NO_FLUSH;
>>  		delalloc_lock = false;
>> -	} else if (current->journal_info) {
>> -		flush = BTRFS_RESERVE_FLUSH_LIMIT;
>> -	}
>> +	} else {
>> +		if (current->journal_info)
>> +			flush = BTRFS_RESERVE_FLUSH_LIMIT;
>>  
>> -	if (flush != BTRFS_RESERVE_NO_FLUSH &&
>> -	    btrfs_transaction_in_commit(fs_info))
>> -		schedule_timeout(1);
>> +		if (btrfs_transaction_in_commit(fs_info))
>> +			schedule_timeout(1);
>>  
>> -	if (delalloc_lock)
>>  		mutex_lock(&inode->delalloc_mutex);
>> +	}
> 
> Squeezing the condition branches makes the code more readable, I have
> only one objection and it's the mutex_lock. It IMHO looks better when
> it's a separate branch as it pairs with the unlock:
> 
> if (delalloc_lock)
> 	mutex_lock(...);
> 
> ...
> 
> if (delalloc_lock)
> 	mutex_unlock(...);
> 
> In your version it's implied by the first if that checks
> btrfs_is_free_space_inode and delalloc_lock is hidden there.
> 

My line of thought when developing the patch was that delalloc is
another level of indirection and. What I wanted to achieve in the end is
to make it clear that delalloc_mutex really depends on whether we are
reserving for the freespace inode or not.

>>  
>>  	num_bytes = ALIGN(num_bytes, fs_info->sectorsize);
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