Re: Ext4 developers get-together at the Collab Summit

[Tao Ma <tm@tao.ma>]

On 01/17/2013 09:15 PM, Zheng Liu wrote:
> Hello Ted,
> 
> On Mon, Jan 14, 2013 at 09:48:00AM -0500, Theodore Ts'o wrote:
>> Hi,
>>
>> 	The Linux Foundation's Collaboration Summit is April 15-17th,
>> and the Linux Storage, File System, and MM Summit is April 18-19th in
>> San Francisco (at the Parc 55 hotel).
>>
>> 	I'd like to organize an ext4 developer's meeting during the
>> Collab Summit sometime April 15-17th, since so many of us will hopefully
>> be attending LSF.  (The CFP will hopefully be coming soon for LSF.)
>>
>> 	If you're interested in attending, please reply to this thread,
>> and include some suggested topics that you'd be interested in
>> discussing.  Based on the number of topics and the number of people who
>> are planning on attending, I'll know how much time we need to reserve
>> and how big of a room to request.
>>
>> 	Also, if you need a invitation letter for Visa purposes, also
>> please let me know.  I can arrange for the Linux Foundation to get that
>> letter sent, so that folks have enough time to get a Visa.
> 
> Tao and I would like to attend the ext4 workshop this year.  Here are some
> topics that we want to discuss with other folks at this meeting.
> 
> * Optimization for different devices
>   We can consume more resources (e.g. Memory) for Flash/SSD device to get a
> better performance.  Meanwhile we want to reduce the consumption and provide
> a best effort performance for HDD in a low-end server with a ARM CPU, only 1G
> memory, and 4 x 3T disks.  This are two different directions of optimization.
To be more precisely we are willing to do improvements for the 2 scenarios:
1. high end servers with very fast SSDs like FusionIO, we want to do
file read/write as fast as possible.
2. low end servers with cpu like ARM, small memory and large volumes. In
this case, we want to save cpu power and memory usage.

One more thing Zheng forgot to mention is the ability to do online fsck.
That may be a new direction and we actually haven't think much about it yet.

Thanks,
Tao
> 
> * Stable tree and long-term tree
>   I remember that Ted has talked about ext4 stable and long-term tree.  So we
> can discuss in this meeting how to maintain them and other detail.
> 
> * Extent tree disk layout
>   In this mail [1], Ted metioned that extent structure could be extented to
> support larger file, such as 64-bits physical block, bigger logical block, and
> using cluster-size as unit in extent.  All these can make us better support
> large filesystem.
> 
> 1. http://comments.gmane.org/gmane.comp.file-systems.ext4/35490
> 
> * Block allocation hint
>   An interface (e.g. ioctl(2)) is provided to let the app give a block
> allocation hint.  Filesystem can allocate some blocks that can be read/written
> faster than other blocks for a file, such as allocating blocks on outter track
> in HDD.
> 
> * Latency
>   Chris had presented a proposal that is 'data=guarded', which aims at imporving
> the latency of sync.  We can discuss how to provide stable latency in ext4.
> Forgive me that I compare two filesystems here, but the result of the following
> test case shows that the latency of ext4 is higher than xfs's.  So maybe we can
> improve it.
> 
> I use 'fio' to do the following test.  I revert the patches of stable page write
> for avoiding the impact of it.  Meanwhile I disable delalloc feature in ext4.  I
> repeat the test case serveral times, but the result of ext4 is higher than xfs.
> 
> [global]
> iodepth=1
> directory=/mnt/sda3
> direct=0
> group_reporting
> thread
> fallocate=0
> runtime=120
> 
> [log-append]
> ioengine=sync
> rw=write
> bs=4k
> size=10g
> filesize=10g
> rate=5m
> numjobs=1
> 
> I pick the best result of two filesystems and paste them here.
> 
> [ext4]
>   write: io=614404KB, bw=5119.2KB/s, iops=1279 , runt=120001msec
>     clat (usec): min=11 , max=149 , avg=14.12, stdev= 1.73
>      lat (usec): min=11 , max=150 , avg=14.54, stdev= 1.81
> 
> [xfs]
>   write: io=614404KB, bw=5119.2KB/s, iops=1279 , runt=120001msec
>     clat (usec): min=4 , max=89 , avg= 8.42, stdev= 1.85
>      lat (usec): min=4 , max=89 , avg= 8.80, stdev= 1.94
> 
> 
> BTW, Tao and I need a invitation letter for applying our visa.  Please let me
> know if there are something we need to do.
> 
> Thanks,
> 						- Zheng
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