[Devel] Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

[David Rientjes]

On Tue, 26 Jun 2012, Glauber Costa wrote:

> > Nope, have you checked the output of /sys/kernel/slab/.../order when
> > running slub?  On my workstation 127 out of 316 caches have order-2 or
> > higher by default.
> > 
> 
> Well, this is still on the side of my argument, since this is still a majority
> of them being low ordered.

Ok, so what happens if I pass slub_min_order=2 on the command line?  We 
never retry?

> The code here does not necessarily have to retry -
> if I understand it correctly - we just retry for very small allocations
> because that is where our likelihood of succeeding is.
> 

Well, the comment for NR_PAGES_TO_RETRY says

	/*
	 * We need a number that is small enough to be likely to have been
	 * reclaimed even under pressure, but not too big to trigger unnecessary 
	 * retries
	 */

and mmzone.h says

	/*
	 * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed
	 * costly to service.  That is between allocation orders which should
	 * coalesce naturally under reasonable reclaim pressure and those which
	 * will not.
	 */
	#define PAGE_ALLOC_COSTLY_ORDER 3

so I'm trying to reconcile which one is correct.