linux-kernel - Re: [RT LATENCY] 249 microsecond latency caused by slub's unfreeze

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Message-ID: <0000013f0b7b993c-35844ed2-81be-4146-ab3c-6c803006576b-000000@email.amazonses.com>
Date:	Mon, 3 Jun 2013 19:20:17 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	JoonSoo Kim <js1304@...il.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark@...hat.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [RT LATENCY] 249 microsecond latency caused by slub's
 unfreeze_partials() code.

On Tue, 4 Jun 2013, JoonSoo Kim wrote:

> And I re-read Steven initial problem report in RT kernel and find that
> unfreeze_partial() do lock and unlock several times. This means that
> each page in cpu partial list doesn't come from same node. Why do we
> add other node's slab to this cpu partial list? This is also not good
> for general case. How about considering node affinity in __slab_free()?
> IMHO, if we implement this, Steven's problem can be solved.

We may need the other nodes pages if we consistently allocate from there.
__slab_alloc() ensures that only pages from the correct node are used. It
will drop pages that do not come from the proper nodes.

Filtering in __slab_free would mean that we cannot improve performance on
remote frees.

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