High Fragmentation with XFS and NFS Sync

[Nick Fisk]

On 3 Jul 2016 1:34 p.m., "Stefan Ring" <stefanrin at gmail.com> wrote:
>
> On Sat, Jul 2, 2016 at 10:52 AM, Nick Fisk <friskyfisk10 at googlemail.com>
wrote:
> > Hi, hope someone can help me here.
> >
> > I'm exporting some XFS fs's to ESX via NFS with the sync option
enabled. I'm
> > seeing really heavy fragmentation when multiple VM's are copied onto the
> > share at the same time. I'm also seeing kmem_alloc failures, which is
> > probably the biggest problem as this effectively takes everything down.
> >
>
> The same thing happens with MySQL's InnoDB files if O_DIRECT is in use.
>
> The kmem_alloc failure taking everything down is most likely a result
> of you calling xfs_bmap on these files and does not happen during
> normal use. I've had the same experience some time ago.

Unfortunately this did happen during normal use. It occurred over night
after kicking a bunch copies off. Something like 5 million extents for
10-20 files. I suspect as suggested, it's to do with memory fragmentation.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://oss.sgi.com/pipermail/xfs/attachments/20160703/ca4cda0e/attachment.html>