linux-kernel - Re: [PATCH 3/7] slub: Do not use c->page on free

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Message-ID: <alpine.DEB.2.11.1412150815210.20101@gentwo.org>
Date:	Mon, 15 Dec 2014 08:16:00 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org, penberg@...nel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 3/7] slub: Do not use c->page on free

On Mon, 15 Dec 2014, Joonsoo Kim wrote:

> > +static bool same_slab_page(struct kmem_cache *s, struct page *page, void *p)
> > +{
> > +	long d = p - page->address;
> > +
> > +	return d > 0 && d < (1 << MAX_ORDER) && d < (compound_order(page) << PAGE_SHIFT);
> > +}
> > +
>
> Somtimes, compound_order() induces one more cacheline access, because
> compound_order() access second struct page in order to get order. Is there
> any way to remove this?

I already have code there to avoid the access if its within a MAX_ORDER
page. We could probably go for a smaller setting there. PAGE_COSTLY_ORDER?

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