Re: OOM-killer for zone DMA?

[Takashi Iwai <tiwai@suse.de>]

At Mon, 30 Aug 2004 20:36:57 +1000,
Nick Piggin wrote:
> 
> Takashi Iwai wrote:
> > At Sat, 28 Aug 2004 16:10:02 +1000,
> > Nick Piggin wrote:
> > 
> 
> >>
> >>You at least need __GFP_NORETRY to achieve what you want.
> > 
> > 
> > Yes, with that flag it can be avoided.
> > 
> 
> Great.
> 
> > But it *should* retry.
> 
> That is precisely the opposite of what you want.

I mean, retrying for zone NORMAL pages should be ok.


> >  It's an allocation of single page, and the
> > caller of dma_alloc_coherent() doesn't know whether it's allocated
> > from zone DMA or zone normal.  It sets just the coherent_dma_mask to a
> > value less than 32 bit.
> > 
> > This situation may happen even after applying my patch.
> > If you have more RAM than mask, allocation in the zone NORMAL may hit
> > the outside of mask, and tries the zone DMA as fallback, although
> > there are pretty enough free RAM in the zone NORMAL.
> > 
> > So, triggering oom-killer for zone DMA is non-sense, IMO.
> > 
> 
> AFAIKS your patch tries ZONE_NORMAL, then falls back to ZONE_DMA, in
> which case you possibly do want the oom-killer for ZONE_DMA. Although
> if ZONE_DMA gets filled with pinned memory it will take down the system
> due to the continual oom-killing :(

Yes, that's what annoyed me.
Pages allocated in zone DMA are usually buffers for drivers, which
won't be released by oom-killer.

Meanwhile, I fixed the driver codes to always add __GFP_NORETRY to
avoid oom-killer...

> If the interface is allowed to fail, it may be an idea to allow it.
> I'm not really sure... the other thing might be to do the retries in
> the caller (ie. your code).


Takashi
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