Date: Thu, 3 Dec 2015 09:16:47 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Chris Snook <chris.snook@gmail.com>
Cc: David Miller <davem@davemloft.net>, 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
Message-ID: <20151203081646.GB9264@dhcp22.suse.cz>
References: <20151127082010.GA2500@dhcp22.suse.cz>
 <20151128145113.GB4135@amd>
 <20151130132129.GB21950@dhcp22.suse.cz>
 <20151201.153517.224543138214404348.davem@davemloft.net>
 <CAMXMK6u1vQ772SGv-J3cKvOmS6QRAjjQLYiSiWO2+T=HRTiK1A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CAMXMK6u1vQ772SGv-J3cKvOmS6QRAjjQLYiSiWO2+T=HRTiK1A@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1620
Lines: 41

On Wed 02-12-15 22:43:31, Chris Snook wrote:
> 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.

Why would GFP_KERNEL order-4 allocation hang? It will fail if there are
not >=4 order pages available even after reclaim and/or compaction.
GFP_ATOMIC allocations should be used only when an access to memory
reserves is really required. If the allocation just doesn't want to
invoke direct reclaim then GFP_NOWAIT is a more suitable alternative.

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/