Re: [PATCH] Improve Atheros ethernet driver not to do order 4 GFP_ATOMIC allocation

From: Chris Snook <chris.snook@gmail.com>
To: David Miller <davem@davemloft.net>, mhocko@kernel.org
Cc: pavel@ucw.cz, akpm@osdl.org, linux-kernel@vger.kernel.org,
	jcliburn@gmail.com, netdev@vger.kernel.org, rjw@rjwysocki.net,
	linux-mm@kvack.org, nic-devel@qualcomm.com, ronangeles@gmail.com,
	ebiederm@xmission.com
Subject: Re: [PATCH] Improve Atheros ethernet driver not to do order 4 GFP_ATOMIC allocation
Date: Wed, 02 Dec 2015 22:43:31 +0000	[thread overview]
Message-ID: <CAMXMK6u1vQ772SGv-J3cKvOmS6QRAjjQLYiSiWO2+T=HRTiK1A@mail.gmail.com> (raw)
In-Reply-To: <20151201.153517.224543138214404348.davem@davemloft.net>

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On Tue, Dec 1, 2015 at 12:35 PM David Miller <davem@davemloft.net> wrote:

> From: Michal Hocko <mhocko@kernel.org>
> Date: Mon, 30 Nov 2015 14:21:29 +0100
>
> > On Sat 28-11-15 15:51:13, Pavel Machek wrote:
> >>
> >> atl1c driver is doing order-4 allocation with GFP_ATOMIC
> >> priority. That often breaks  networking after resume. Switch to
> >> GFP_KERNEL. Still not ideal, but should be significantly better.
> >
> > It is not clear why GFP_KERNEL can replace GFP_ATOMIC safely neither
> > from the changelog nor from the patch context.
>
> Earlier in the function we do a GFP_KERNEL kmalloc so:
>
> ¯\_(ツ)_/¯
>
> It should be fine.
>

AFAICT, the people who benefit from GFP_ATOMIC are the people running all
their storage over NFS/iSCSI who are suspending their machines while
they're so busy they don't have any clean order 4 pagecache to drop, and
want the machine to panic rather than hang. The people who benefit from
GFP_KERNEL are the people who use their laptop for a while, put it to
sleep, and then wake it up again. I think the latter is the use case we
should be optimizing for.

-- Chris

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