Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH RESEND 4/8] ext4: add the gdt block of meta_bg to
 system_zone
To:     "Theodore Y. Ts'o" <tytso@mit.edu>
Cc:     adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org
References: <1604764698-4269-1-git-send-email-brookxu@tencent.com>
 <1604764698-4269-4-git-send-email-brookxu@tencent.com>
 <20201203150841.GM441757@mit.edu>
From:   brookxu <brookxu.cn@gmail.com>
Message-ID: <6d061665-f66e-9af4-5f91-fe0e4902bce8@gmail.com>
Date:   Fri, 4 Dec 2020 09:29:35 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.5.0
MIME-Version: 1.0
In-Reply-To: <20201203150841.GM441757@mit.edu>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


Theodore Y. Ts'o wrote on 2020/12/3 23:08:
> On Sat, Nov 07, 2020 at 11:58:14PM +0800, Chunguang Xu wrote:
>> From: Chunguang Xu <brookxu@tencent.com>
>>
>> In order to avoid poor search efficiency of system_zone, the
>> system only adds metadata of some sparse group to system_zone.
>> In the meta_bg scenario, the non-sparse group may contain gdt
>> blocks. Perhaps we should add these blocks to system_zone to
>> improve fault tolerance without significantly reducing system
>> performance.
> 
>> @@ -226,13 +227,16 @@ int ext4_setup_system_zone(struct super_block *sb)
>>  
>>  	for (i=0; i < ngroups; i++) {
>>  		cond_resched();
>> -		if (ext4_bg_has_super(sb, i) &&
>> -		    ((i < 5) || ((i % flex_size) == 0))) {
>> -			ret = add_system_zone(system_blks,
>> -					ext4_group_first_block_no(sb, i),
>> -					ext4_bg_num_gdb(sb, i) + 1, 0);
>> -			if (ret)
>> -				goto err;
>> +		if ((i < 5) || ((i % flex_size) == 0)) {
> 
> If we're going to do this, why not just drop the above conditional,
> and just always do this logic for all block groups?

Thanks, in the large disk scenario, if we deal with all groups, the
system_zone will be very large, which may reduce performance. I think
the previous method is good, but it needs to be changed slightly, so
that the fault tolerance in the meta_bg scenario can be improved
without the risk of performance degradation.

>> +			gd_blks = ext4_bg_has_super(sb, i) +
>> +				ext4_bg_num_gdb(sb, i);
>> +			if (gd_blks) {
>> +				ret = add_system_zone(system_blks,
>> +						ext4_group_first_block_no(sb, i),
>> +						gd_blks, 0);
>> +				if (ret)
>> +					goto err;
>> +			}
> 
> 						- Ted
>