netdev - Re: [PATCH] mlx4: Use GFP_NOFS calls during the ipoib TX path when creating the QP

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Message-ID: <CAJZOPZ+xKFwjrpWnBQDU=CU2XbjP00Qfgj8AYJ1SGHhf8U9O-A@mail.gmail.com>
Date:	Wed, 5 Mar 2014 21:46:26 +0200
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Roland Dreier <roland@...nel.org>, Amir Vadai <amirv@...lanox.com>,
	Eli Cohen <eli@....mellanox.co.il>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eugenia Emantayev <eugenia@...lanox.com>,
	"David S. Miller" <davem@...emloft.net>,
	Mel Gorman <mgorman@...e.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mlx4: Use GFP_NOFS calls during the ipoib TX path when
 creating the QP

On Wed, Feb 26, 2014 at 12:11 AM, Jiri Kosina <jkosina@...e.cz> wrote:
> The problem encountered was described as follows:
>         It's not memory reclamation that is the problem as such. There is
>         an indirect dependency between network filesystems writing back
>         pages and ipoib_cm_tx_init() due to how a kworker is used. Page
>         reclaim cannot make forward progress until ipoib_cm_tx_init()
>         succeeds and it is stuck in page reclaim itself waiting for network
>         transmission. Ordinarily this sitaution may be avoided by having
>         the caller use GFP_NOFS but ipoib_cm_tx_init() does not have
>         that information.

So to hit the bug, one just needs to attempt doing NFS client mount
over an IP subnet served by IPoIB NIC that uses connected-mode and
runs over mlx4 device?  Or this happens when  the connection is going
through teardown/re-establishment or something else?
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