Re: [PATCH v4 4/4] btrfs: increase metadata alloc size to 5GB for volumes > 50GB

[Stefan Roesch <shr@fb.com>]

On 11/5/21 3:11 AM, Nikolay Borisov wrote:
> 
> 
> On 29.10.21 г. 21:39, Stefan Roesch wrote:
>> This increases the metadata default allocation size from 1GB to 5GB for
>> volumes with a size greater than 50GB.
> 
> Imo such a change would warrant more data about why it's ok. Clearly
> there is some internal facebook workload which benefits from this,
> however this doesn't automatically mean it will be beneficial for the
> wider user base. Also your cover letter doesn't contain any more
> specifics about the particular workload. Isn't 5g a bit too steep,
> perhaps 2 is larger and yet more conservative?
>

I understand that this change is getting some questions and a more conservative
value might need to be chosen. Let's wait until all the reviews are in and
then settle on a compromise. 
 
> 
>>
>> Signed-off-by: Stefan Roesch <shr@fb.com>
>> ---
>>  fs/btrfs/space-info.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
>> index 7370c152ce8a..44507262c515 100644
>> --- a/fs/btrfs/space-info.c
>> +++ b/fs/btrfs/space-info.c
>> @@ -195,7 +195,7 @@ static u64 compute_chunk_size_regular(struct btrfs_fs_info *info, u64 flags)
>>  
>>  	/* Handle BTRFS_BLOCK_GROUP_METADATA */
>>  	if (info->fs_devices->total_rw_bytes > 50ULL * SZ_1G)
>> -		return SZ_1G;
>> +		return 5ULL * SZ_1G;
>>  
>>  	return SZ_256M;
>>  }
>>