Re: deadlock with latest xfs

[Nick Piggin <nickpiggin@yahoo.com.au>]

On Tuesday 28 October 2008 17:25, Dave Chinner wrote:
> 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...

I suppose it could have been getting oom-killed, then failing the
alloc, then oopsing on the way out, yes.

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