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

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Message-ID: <20090628101654.GB8673@ucw.cz>
Date:	Sun, 28 Jun 2009 12:16:55 +0200
From:	Pavel Machek <pavel@....cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, 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 2009-06-24 12:46:02, Linus Torvalds wrote:
> 
> 
> 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.

Ok, so we should re-add that 4MB buffer to suspend, so that
allocations work even during that, right?

...and... if you do enough of small allocations, they *will* have to
fail at some point. Maybe linux is now mature enough and running on
small enough devices that it makes sense to start handling that?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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