linux-kernel - Re: [patch] SLQB slab allocator

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Date:	Sat, 24 Jan 2009 04:09:26 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Lin Ming <ming.m.lin@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] SLQB slab allocator

On Saturday 24 January 2009 03:10:17 Nick Piggin wrote:
> On Fri, Jan 23, 2009 at 10:52:43AM -0500, Christoph Lameter wrote:
> > On Fri, 23 Jan 2009, Nick Piggin wrote:
> > > > Typically we traverse lists of objects that are in the same slab
> > > > cache.
> > >
> > > Very often that is not the case. And the price you pay for that is that
> > > you have to drain and switch freelists whenever you encounter an object
> > > that is not on the same page.
> >
> > SLUB can directly free an object to any slab page. "Queuing" on free via
> > the per cpu slab is only possible if the object came from that per cpu
> > slab. This is typically only the case for objects that were recently
> > allocated.
>
> Ah yes ok that's right. But then you don't get LIFO allocation
> behaviour for those cases.

And actually really this all just stems from conceptually in fact you
_do_ switch to a different queue (from the one being allocated from)
to free the object if it is on a different page. Because you have a
set of queues (a queue per-page). So freeing to a different queue is
where you lose LIFO property.

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