linux-kernel - Re: [15/17] SLUB: Support virtual fallback via SLAB

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Date:	Mon, 1 Oct 2007 13:55:29 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK

On Sat, 29 Sep 2007, Andrew Morton wrote:

> > atomic allocations. And with SLUB using higher order pages, atomic !0
> > order allocations will be very very common.
> 
> Oh OK.
> 
> I thought we'd already fixed slub so that it didn't do that.  Maybe that
> fix is in -mm but I don't think so.
> 
> Trying to do atomic order-1 allocations on behalf of arbitray slab caches
> just won't fly - this is a significant degradation in kernel reliability,
> as you've very easily demonstrated.

Ummm... SLAB also does order 1 allocations. We have always done them.

See mm/slab.c

/*
 * Do not go above this order unless 0 objects fit into the slab.
 */
#define BREAK_GFP_ORDER_HI      1
#define BREAK_GFP_ORDER_LO      0
static int slab_break_gfp_order = BREAK_GFP_ORDER_LO;

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