On Thu, May 02, 2013 at 08:03:04AM +1000, Dave Chinner wrote:
> On Wed, May 01, 2013 at 08:57:38AM -0700, David Rientjes wrote:
> > On Wed, 1 May 2013, Shawn Bohrer wrote:
> >
> > > I've got two compute clusters with around 350 machines each which are
> > > running kernels based off of 3.1.9 (Yes I realize this is ancient by
> > > todays standards).
>
> xfs_info output of one of those filesystems? What platform are you
> running (32 or 64 bit)?
# cat /proc/mounts | grep data-cache
/dev/sdb1 /data-cache xfs rw,nodiratime,relatime,attr2,delaylog,noquota 0 0
# xfs_info /data-cache
meta-data=/dev/sdb1 isize=256 agcount=4, agsize=66705344 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=266821376, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal bsize=4096 blocks=130283, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
These are 64-bit systems. The ones that hit the issue more frequently
have 96 GB of RAM.
> > > All of the machines run a 'find' command once an
> > > hour on one of the mounted XFS filesystems. Occasionally these find
> > > commands get stuck requiring a reboot of the system. I took a peek
> > > today and see this with perf:
> > >
> > > 72.22% find [kernel.kallsyms] [k] _raw_spin_lock
> > > |
> > > --- _raw_spin_lock
> > > |
> > > |--98.84%-- vm_map_ram
> > > | _xfs_buf_map_pages
> > > | xfs_buf_get
> > > | xfs_buf_read
> > > | xfs_trans_read_buf
> > > | xfs_da_do_buf
> > > | xfs_da_read_buf
> > > | xfs_dir2_block_getdents
> > > | xfs_readdir
> > > | xfs_file_readdir
> > > | vfs_readdir
> > > | sys_getdents
> > > | system_call_fastpath
> > > | __getdents64
> > > |
> > > |--1.12%-- _xfs_buf_map_pages
> > > | xfs_buf_get
> > > | xfs_buf_read
> > > | xfs_trans_read_buf
> > > | xfs_da_do_buf
> > > | xfs_da_read_buf
> > > | xfs_dir2_block_getdents
> > > | xfs_readdir
> > > | xfs_file_readdir
> > > | vfs_readdir
> > > | sys_getdents
> > > | system_call_fastpath
> > > | __getdents64
> > > --0.04%-- [...]
> > >
> > > Looking at the code my best guess is that we are spinning on
> > > vmap_area_lock, but I could be wrong. This is the only process
> > > spinning on the machine so I'm assuming either another process has
> > > blocked while holding the lock, or perhaps this find process has tried
> > > to acquire the vmap_area_lock twice?
> > >
> >
> > Significant spinlock contention doesn't necessarily mean that there's a
> > deadlock, but it also doesn't mean the opposite. Depending on your
> > definition of "occassionally", would it be possible to run with
> > CONFIG_PROVE_LOCKING and CONFIG_LOCKDEP to see if it uncovers any real
> > deadlock potential?
>
> It sure will. We've been reporting that vm_map_ram is doing
> GFP_KERNEL allocations from GFP_NOFS context for years, and have
> reported plenty of lockdep dumps as a result of it.
>
> But that's not the problem that is occurring above - lockstat is
> probably a good thing to look at here to determine exactly what
> locks are being contended on....
I've built a kernel with lock_stat, CONFIG_PROVE_LOCKING,
CONFIG_LOCKDEP and have one machine running with that kernel. We'll
probably put machines on this debug kernel when we reboot them and
hopefully one will trigger the issue.
Thanks,
Shawn
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