linux-kernel - Re: [Q] Default SLAB allocator

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Message-ID: <CAAmzW4N1rAQLOE3QmeeTfsNH-7v-9RD8wT990RbZtYon3YfrLA@mail.gmail.com>
Date:	Fri, 19 Oct 2012 09:03:58 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Ezequiel Garcia <elezegarcia@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Tim Bird <tim.bird@...sony.com>,
	celinux-dev@...ts.celinuxforum.org
Subject: Re: [Q] Default SLAB allocator

Hello, Eric.
Thank you very much for a kind comment about my question.
I have one more question related to network subsystem.
Please let me know what I misunderstand.

2012/10/14 Eric Dumazet <eric.dumazet@...il.com>:
> In latest kernels, skb->head no longer use kmalloc()/kfree(), so SLAB vs
> SLUB is less a concern for network loads.
>
> In 3.7, (commit 69b08f62e17) we use fragments of order-3 pages to
> populate skb->head.

You mentioned that in latest kernel skb->head no longer use kmalloc()/kfree().
But, why result of David's "netperf RR" test on v3.6 is differentiated
by choosing the allocator?
As far as I know, __netdev_alloc_frag may be introduced in v3.5, so
I'm just confused.
Does this test use __netdev_alloc_skb with "__GFP_WAIT | GFP_DMA"?

Does normal workload for network use __netdev_alloc_skb with
"__GFP_WAIT | GFP_DMA"?

Thanks!
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