linux-kernel - Re: upcoming kerneloops.org item: get_page_from

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Date:	Wed, 24 Jun 2009 12:46:02 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	penberg@...helsinki.fi, arjan@...radead.org,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	npiggin@...e.de
Subject: Re: upcoming kerneloops.org item: get_page_from_freelist



On Wed, 24 Jun 2009, Andrew Morton wrote:

> On Wed, 24 Jun 2009 12:16:20 -0700 (PDT)
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > Lookie here. This is 2.6.0:mm/page_alloc.c:
> > 
> >         do_retry = 0;
> >         if (!(gfp_mask & __GFP_NORETRY)) {
> >                 if ((order <= 3) || (gfp_mask & __GFP_REPEAT))
> >                         do_retry = 1;
> >                 if (gfp_mask & __GFP_NOFAIL)
> >                         do_retry = 1;
> >         }
> >         if (do_retry) {
> >                 blk_congestion_wait(WRITE, HZ/50);
> >                 goto rebalance;
> >         }
> 
> rebalance:
> 	if ((p->flags & (PF_MEMALLOC | PF_MEMDIE)) && !in_interrupt()) {
> 		/* go through the zonelist yet again, ignoring mins */
> 		for (i = 0; zones[i] != NULL; i++) {
> 			struct zone *z = zones[i];
> 
> 			page = buffered_rmqueue(z, order, cold);
> 			if (page)
> 				goto got_pg;
> 		}
> 		goto nopage;
> 	}

Your point?

That's the recursive allocation or oom case. Not the normal case at all.

The _normal_ case is to do the whole "try_to_free_pages()" case and try 
and try again. Forever.

IOW, we have traditionally never failed small kernel allocations. It makes 
perfect sense that people _depend_ on that.

Now, we have since relaxed that (a lot). And in answer to that, people 
have added more __GFP_NOFAIL flags, I bet. It's all very natural. Claiming 
that this is some "new error" and that we should warn about NOFAIL 
allocations with big orders is just silly and simply not true.

		Linus


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