Re: [Bug 16148] New: page allocation failure. order:1, mode:0x50d0

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 11 Jun 2010 10:46:07 +0200 Thomas Hellstrom <thellstrom@vmware.com> wrote:

> >>>
> >>>        
> >> David, I have a vague feeling that we've been round this loop before..
> >>
> >> Why does agp_alloc_page_array() use __GFP_NORETRY?  It's pretty unusual
> >> and it's what caused this spew.
> >>
> >> There's nothing in the changelog and the only relevant commentary
> >> appears to be "This speeds things up and also saves memory for small
> >> AGP regions", which is inscrutable.  Can you please add a usable
> >> comment there?
> >>      
> > cc'ing Thomas, who added this, I expect we could drop the NORETRY or
> > just add NOWARN. Though an order 1 page alloc failure isn't a pretty
> > sight, not sure how a vmalloc fallback could save us.
> >
> >    
> 
> Hmm. IIRC that was an untested speed optimization back from the time 
> when I was
> reading ldd3. I think the idea was to avoid slow allocations of (order > 
> 0) if they weren't
> immediately available and fall back to vmalloc single page allocations.
> It might be that that functionality is no longer preserved and only the 
> __GFP_NORETRY remains.
> I think it should be safe to remove the NORETRY if it's annoying, but it 
> should probably be equally safe to add a NOWARN and keep the vmalloc 
> fallback.

An order-1 GFP_KERNEL allocation is a breeze - slub does them often, we
use them for kernel stacks all the time.  I'd say just remove the
__GFP_NORETRY and be happy.

In fact if the allocations are always this small I'd say we can remove
the vmalloc fallback too.  However if under some circumstances the
allocations can be "large", say order-4 or higher then allocation
failures are still a risk.