Re: [PATCH] Deadlock during heavy write activity to userspace NFS

[Nick Piggin]

Avi Kivity wrote:
> Ulrich Weigand wrote:
>
> > Avi Kivity wrote:
> >
> >  
> >
> > > In our case, all block I/O is done using unbuffered I/O, and all 
> > > memory is preallocated, so we don't need kswapd at all, just that 
> > > small bit of memory that syscalls consume.
> > >   
> >
> >
> > Does your userspace process need to send/receive network packets
> > in order to perform a write-out? 
>
> Yes.
>
> > If so, how can you make sure your
> > incoming packets aren't thrown away in out-of-memory situations?
> > (Outgoing packets can use PF_MEMALLOC memory I guess, but incoming
> > ones aren't associated to any process yet ...)
> >
> >  
> I did nothing to address this. So far it works well, even under heavy 
> load. I guess a general solution needs to address this as well.
>
> The kernel NFS client (which kswapd depends on) has the same issue. Has 
> anyone ever observed kswapd deadlock due to imcoming or outgoing NFS 
> packets being discarded due to oom?

Yes this has been observed.

alloc_skb on the client needs to somehow know that traffic coming
from the server is "MEMALLOC" and allowed to use memory reserves.
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