[dm-devel] [Lsf] Preliminary Agenda and Activities for LSF

[Mingming Cao]

On Tue, 2011-03-29 at 07:16 -0400, Ric Wheeler wrote:
> On 03/29/2011 12:36 AM, James Bottomley wrote:
> > Hi All,
> >
> > Since LSF is less than a week away, the programme committee put together
> > a just in time preliminary agenda for LSF.  As you can see there is
> > still plenty of empty space, which you can make suggestions (to this
> > list with appropriate general list cc's) for filling:
> >
> > https://spreadsheets.google.com/pub?hl=en&hl=en&key=0AiQMl7GcVa7OdFdNQzM5UDRXUnVEbHlYVmZUVHQ2amc&output=html
> >
> > If you don't make suggestions, the programme committee will feel
> > empowered to make arbitrary assignments based on your topic and attendee
> > email requests ...
> >
> > We're still not quite sure what rooms we will have at the Kabuki, but
> > we'll add them to the spreadsheet when we know (they should be close to
> > each other).
> >
> > The spreadsheet above also gives contact information for all the
> > attendees and the programme committee.
> >
> > Yours,
> >
> > James Bottomley
> > on behalf of LSF/MM Programme Committee
> >
> 
> Here are a few topic ideas:
> 
> (1)  The first topic that might span IO & FS tracks (or just pull in device 
> mapper people to an FS track) could be adding new commands that would allow 
> users to grow/shrink/etc file systems in a generic way.  The thought I had was 
> that we have a reasonable model that we could reuse for these new commands like 
> mount and mount.fs or fsck and fsck.fs. With btrfs coming down the road, it 
> could be nice to identify exactly what common operations users want to do and 
> agree on how to implement them. Alasdair pointed out in the upstream thread that 
> we had a prototype here in fsadm.
> 
> (2) Very high speed, low latency SSD devices and testing. Have we settled on the 
> need for these devices to all have block level drivers? For S-ATA or SAS 
> devices, are there known performance issues that require enhancements in 
> somewhere in the stack?
> 
> (3) The union mount versus overlayfs debate - pros and cons. What each do well, 
> what needs doing. Do we want/need both upstream? (Maybe this can get 10 minutes 
> in Al's VFS session?)
> 

Ric,

May I propose some discussion about concurrent direct IO support for
ext4?

Direct IO write are serialized by the single i_mutex lock.  This lock
contention becomes significant when running database or direct IO heavy
workload on guest, where  the host pass a file image to guest as a block
device. All the parallel IOs in guests are being serialized by the
i_mutex lock on the host disk image file. This greatly penalize the data
base application performance in KVM. 

I am looking for some discussion about removing the i_mutex lock in the
direct IO write code path for ext4, when multiple threads are
direct write to different offset of the same file. This would require
some way to track the in-fly DIO IO range, either done at ext4 level or
above th vfs layer. 


Thanks,