Re: deadlock with latest xfs

Dave Chinner
2008-10-28T06:25:41Z

On Tue, Oct 28, 2008 at 05:02:16PM +1100, Nick Piggin wrote:
> On Sunday 26 October 2008 13:50, Dave Chinner wrote:
>
> > [1] I don't see how any of the XFS changes we made make this easier to hit.
> > What I suspect is a VM regression w.r.t. memory reclaim because this is
> > the second problem since 2.6.26 that appears to be a result of memory
> > allocation failures in places that we've never, ever seen failures before.
> >
> > The other new failure is this one:
> >
> > http://bugzilla.kernel.org/show_bug.cgi?id=11805
> >
> > which is an alloc_pages(GFP_KERNEL) failure....
> >
> > mm-folk - care to weight in?
>
> order-0 alloc page GFP_KERNEL can fail sometimes. If it is called
> from reclaim or PF_MEMALLOC thread; if it is OOM-killed; fault
> injection.
>
> This is even the case for __GFP_NOFAIL allocations (which basically
> are buggy anyway).
>
> Not sure why it might have started happening, but I didn't see
> exactly which alloc_pages you are talking about? If it is via slab,
> then maybe some parameters have changed (eg. in SLUB) which is
> using higher order allocations.

In fs/xfs/linux-2.6/xfs_buf.c::xfs_buf_get_noaddr(). It's doing a
single page allocation at a time.

It may be that this failure is caused by an increase base memory
consumption of the kernel as this failure was reported in an lguest
and reproduced with a simple 'modprobe xfs ; mount /dev/xxx
/mnt/xfs' command. Maybe the lguest had very little memory available
to begin with and trying to allocate 2MB of pages for 8x256k log
buffers may have been too much for it...