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Re: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250)

To: xfs@xxxxxxxxxxx
Subject: Re: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250)
From: Emmanuel Lacour <elacour@xxxxxxxxxxxxxxx>
Date: Mon, 9 Dec 2013 10:47:15 +0100
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131203125057.GU10988@dastard>
References: <20131128091322.GC5337@xxxxxxxxxxxxxxx> <20131128100521.GO10988@dastard> <20131203095357.GC5405@xxxxxxxxxxxxxxx> <20131203125057.GU10988@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Dec 03, 2013 at 11:50:57PM +1100, Dave Chinner wrote:

thanks very much for your quick and detailled answer!

> OK, 32GB RAM, no obvious shortage, no dirty or writeback data.
> 2TB SATA drives, 32AGs, only unusual setting is 64k directory block
> size.

yes, the 64k was taken from a too quickly read of advice, I don't think
it's of any help on a ceph cluster but I'm not an FS guru. Is there a
way to lower it at runtime?

> Yup, there's your problem:


> Which, I think, is pretty easy to do. Yup, barely smoke tested patch
> below that demonstrates the fix. Beware - patch may eat babies and
> ask for more. Use it at your own risk!

unfortunatly I cannot test this patch because:

- it's a production cluster and it's currently hard for me to reboot
  nodes (not enough nodes ;))
- just after hiting this problem I saw a kernel 3.11 available on Debian
  backports and decided to upgrade the whole cluster.

since this upgrade, there is no problems anymore ... I cross my fingers

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