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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Nick Piggin <npiggin@suse.de>
Subject: Re: [patch] SLQB slab allocator
Date: Sat, 24 Jan 2009 04:09:26 +1100
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Cc: Christoph Lameter <cl@linux-foundation.org>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Lin Ming <ming.m.lin@intel.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>
References: <20090114150900.GC25401@wotan.suse.de> <alpine.DEB.1.10.0901231042380.32253@qirst.com> <20090123161017.GC14517@wotan.suse.de>
In-Reply-To: <20090123161017.GC14517@wotan.suse.de>
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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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