Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

[David Rientjes]

On Mon, 15 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > I can't agree with that assessment, I don't think it's a desired result to 
> > ever panic the machine regardless of what /proc/sys/vm/panic_on_oom is set 
> > to because a lowmem page allocation fails especially considering, as 
> > mentioned in the changelog, these allocations are never __GFP_NOFAIL and 
> > returning NULL is acceptable.
> > 
> please add
>   WARN_ON((high_zoneidx < ZONE_NORMAL) && (gfp_mask & __GFP_NOFAIL))
> somewhere. Then, it seems your patch makes sense.
> 

high_zoneidx < ZONE_NORMAL is not the only case where this exists: it 
exists for __GFP_NOFAIL allocations that are not __GFP_FS as well and has 
for years, no special handling is now needed.

There should be no cases of either (GFP_DMA | __GFP_NOFAIL, or
GFP_NOFS | __GFP_NOFAIL) in my audit of the kernel code.  And since 
__GFP_NOFAIL is not to be added anymore (see Andrew's dab48dab), there's 
no real reason to add a WARN_ON() here.

> I don't like the "possibility" of inifinte loops.
> 

The possibility of infinite loops has always existed in the page allocator 
for __GFP_NOFAIL allocations, that's precisely why it's deprecated and 
eventually we seek to remove it.
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