linux-ext4 - Re: [PATCH] ext4: dir inode reservation V3

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Date:	Wed, 14 Nov 2007 00:27:19 +0800
From:	Coly Li <coyli@...e.de>
To:	Alex Tomas <bzzz.tomas@...il.com>
CC:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: dir inode reservation V3

Thanks for the feedback :-)

Alex Tomas wrote:
> hmm. so you trade 265% degradation of creation for 40% improvement of
> unlink?
> 
265% degradation is only for creating 50000 empty directories. This is not a common case.
There are 13% improvement on create 15 files in each directories. Total time on creating these
directories and files are 25m6s VS. 24m86s, indeed, dir inode reservation is a little faster.

Maybe most of the people will not create dozens of empty directories in their applications,
therefore IMHO the 265% degradation is acceptable.

If user really need to create so many empty directories, they also can mount the file system without
dir inode reservation to get better performance.

> thanks, Alex
> 
> Coly Li wrote:
>>             normal ext4            ext4 with dir inode reservation
>>     mount options:    -o data=writeback        -o
>> data=writeback,dir_ireserve=low
>>     Create dirs:    real    0m49.101s        real    2m59.703s
>>     Create files:    real    24m17.962s        real    21m8.161s
>>     Unlink all:    real    24m43.788s        real    17m29.862s
>> Creating dirs with dir inode reservation is slower than normal ext4 as
>> predicted, because allocating
>> directory inodes in non-linear order will cause extra hard disk
>> seeking and block I/O. Creating
>> files with dir inode reservation is 13% faster than normal ext4.
>> Unlink all the directories and
>> files is 29.2% faster as expected.
>> When number of directories is increased, the performance improvement
>> will be more considerable. More
>> benchmark result will be posted here if necessary, because I need more
>> time to run more test cases.
> 

-- 
Coly Li
SuSE PRC Labs
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