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

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Date:	Mon, 1 Oct 2007 14:10:06 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mel Gorman <mel@...net.ie>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Chinner <dgc@....com>,
	Jens Axboe <jens.axboe@...cle.com>, akpm@...ux-foundation.org
Subject: Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK

On Fri, 28 Sep 2007, Mel Gorman wrote:

> Minimally, SLUB by default should continue to use order-0 pages. Peter has
> managed to bust order-1 pages with mem=128MB. Admittedly, it was a really
> hostile workload but the point remains. It was artifically worked around
> with min_free_kbytes (value set based on pageblock_order, could also have
> been artifically worked around by dropping pageblock_order) and he eventually
> caused order-0 failures so the workload is pretty damn hostile to everything.

SLAB default is order 1 so is SLUB default upstream.

SLAB does runtime detection of the amount of memory and configures the max 
order correspondingly:

from mm/slab.c:

	/*
         * Fragmentation resistance on low memory - only use bigger
         * page orders on machines with more than 32MB of memory.
         */
        if (num_physpages > (32 << 20) >> PAGE_SHIFT)
                slab_break_gfp_order = BREAK_GFP_ORDER_HI;


We could duplicate something like that for SLUB.


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