linux-ext4 - Re: [PATCH] ext4: Only call update_backups if necessary in online resize.

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Message-ID: <50627BA5.60106@tao.ma>
Date:	Wed, 26 Sep 2012 11:51:01 +0800
From:	Tao Ma <tm@....ma>
To:	Theodore Ts'o <tytso@....edu>
CC:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Only call update_backups if necessary in online
 resize.

On 09/26/2012 11:39 AM, Theodore Ts'o wrote:
> On Mon, Sep 24, 2012 at 11:00:17PM +0800, Tao Ma wrote:
>> @@ -1355,8 +1356,16 @@ exit_journal:
>>  			int gdb_num;
>>  			gdb_num = group / EXT4_BLOCKS_PER_GROUP(sb);
>>  			gdb_bh = sbi->s_group_desc[gdb_num];
>> -			update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
>> -				       gdb_bh->b_size);
>> +			/*
>> +			 * only backup the group descriptor block
>> +			 * which hasn't been updated before.
>> +			 */
>> +			if (old_gdb != gdb_bh->b_blocknr) {
>> +				update_backups(sb, gdb_bh->b_blocknr,
>> +					       gdb_bh->b_data,
>> +					       gdb_bh->b_size);
>> +				old_gdb = gdb_bh->b_blocknr;
>> +			}
>>  		}
>>  	}
> 
> Don't we also need to add a call to update_backups() at the end of the
> loop so we update the backup block descriptors for the very last set
> of block groups?
Why?  If it isn't the same as the previous one, it will be updated. If
it is the same, it don't need to be updated. I don't see what your mean
here.

Thanks
Tao
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