Re: Current topics for LSF10/MM Summit 8-9 August in Boston

Christof Schmitt
2010-06-18T11:41:20Z

On Thu, Jun 17, 2010 at 11:07:30AM -0500, James Bottomley wrote:
> On Thu, 2010-06-17 at 18:00 +0200, Christof Schmitt wrote:
> > On Wed, Jun 16, 2010 at 03:50:59PM -0500, James Bottomley wrote:
> > > Given that we're under two months out, I thought it would be time to
> > > post a summary of the topics we've collected so far (Nick will post the
> > > MM summit ones later). Look this over, and if there's anything missing,
> > > propose it ... or if you have cross Storage/FS/MM topics, post them too.
> > >
> > > Oh, and since we're not the most organised bunch, if you posted a topic
> > > and don't see it in the list, please resend ... we probably lost it in
> > > an email shuffle.
> > >
> > > Current Filesystem Topics:
> > >
> > > Alex Elder Upstream maintainer for XFS, general discussion on FS/IO
> > > Aneesh Kumar Rich-acl patches which work better with NFSv4 acl and CIFS acl
> > > Anshul Madan reflink for NFS
> > > Chuck Lever NFS/IPV6 and NFS O_DIRECT, Wu's read-ahead work, vitro perf tools
> > > Eric Sandeen Advances in testing, TRIM/DISCARD/Alignment, writeback sanity
> > > James Lentini reflink for NFS
> > > Jan Kara Discuss/drive sanity review of writeback and general ext*/jbd
> > > Michael Rubin Writeback scaling
> > > Sage Weil Statlite, generic interface for describing file striping for distributed FS, VFS scalability
> > > Al Viro Sorting out d_revalidate and other dcache issues
> > > Coly Li directory/large file scalability
> > > Sorin Faibish Cache writeback discussion
> > >
> > > Current Storage Topics:
> > >
> > > Eric Seppanen Next generation SSDs, performance implications on Linux I/O
> > > Boaz Harrosh PNFS performance considerations, bio_list based/async raidN for generic use; stable pages for I/O
> > > FUJITA Tomonori SCSI target mode, iSCSI, block layer SG (bsg), sg, IOMMU, DMA issues
> > > Hannes Reinecke libfc/multipath/error handing
> > > James Smart FCOE proposal for rework of the FC sysfs tree, work with Hannes on other transport/SCSI subsystem topics
> > > Jeff Moyer IO scheduler
> > > Joel Becker SAN management plugin
> > > Martin Petersen Updates on DIF/DIX, TRIM/DISCARD/UNMAP, generic support for WRITE_SAME
> > >
> > > Plus some MM summit ones which Nick will summarise.
> > [...]
> >
> > What about the topic "Stable pages while IO"?
> > http://www.spinics.net/lists/linux-scsi/msg44074.html
> >
> > Was it lost during the e-mail shuffle or will it be part of the MM topics?
>
> It's actually listed under 'dma issues' ... but there's really been no
> satisfactory resolution or discussion of how one might be achieved.
> Most filesystems rely on modifications to in-flight pages for efficiency
> and copying every fs I/O page would be horrendous both for performance
> and memory consumption. Nor has there really been an indication that
> it's a serious issue. The two sufferers are DIF and iSCSI checksum.
> The latter generates the checksum late enough that it can just discard
> incorrect pages ... the former might need simply to turn off DIF for
> everything other than DIRECT IO.

It is a serious problem when using DIF, so turning off this feature or
only using XFS and direct i/o does not sound very satisfying. But then
i also see the points that have been discussed and that there is no
simple solution.

Christof