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

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Message-Id: <200902051418.47523.nickpiggin@yahoo.com.au>
Date:	Thu, 5 Feb 2009 14:18:46 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Nick Piggin <npiggin@...e.de>,
	"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 Thursday 05 February 2009 07:09:15 Christoph Lameter wrote:
> On Wed, 4 Feb 2009, Nick Piggin wrote:
> > That's very true, and we touched on this earlier. It is I guess
> > you can say a downside of queueing. But an analogous situation
> > in SLUB would be that lots of pages on the partial list with
> > very few free objects, or freeing objects to pages with few
> > objects in them. Basically SLUB will have to do the extra work
> > in the fastpath.
>
> But these are pages with mostly allocated objects and just a few objects
> free. The SLAB case is far worse: You have N objects on a queue and they
> are keeping possibly N pages away from the page allocator and in those
> pages *nothing* is used.

Periodic queue trimming should prevent this from becoming a big problem.
It will trim away those objects, and so subsequent allocations will come
from new pages and be densely packed. I don't think I've seen a problem
in SLAB reported from this phenomenon, so I'm not too concerned about it
at the moment.


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