Re: [patch] arch: remove __GFP_REPEAT for order-0 allocations

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Tue, Sep 28, 2010 at 02:36:55PM -0700, Andrew Morton wrote:
> On Tue, 28 Sep 2010 03:45:10 -0700 (PDT)
> David Rientjes <rientjes@google.com> wrote:
> 
> > Order-0 allocations, including quicklist_alloc(),  are always under 
> > PAGE_ALLOC_COSTLY_ORDER, so they loop endlessly in the page allocator
> > already without the need for __GFP_REPEAT.
> 
> That's only true for the current implementation of the page allocator.
> 
> If we were to change the page allocator behaviour to not do that (and
> we change it daily!) then all those callsites which wanted __GFP_REPEAT
> behaviour will get broken.  So someone would need to go back and work
> out how to unbreak them, if we remembered.
> 
> Plus there's presumably some documentary benefit in leaving the
> __GFP_REPEATs in there.
> 
> Why are those __GFP_REPEATs present at those callsites?  What were
> developers trying to achieve?

As I understand it, it's come about by way of evolution.  I think (I can't
check) that we had loops in the allocation functions.  These were removed
and replaced by __GFP_REPEATs sometime before the current GIT history
started.

I'd check on bkbits.net which I'm sure will have it, but unfortunately I
can't get access to the history for include/asm-arm/pgalloc.h prior to
its move to arch/arm.

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