linux-kernel - Re: cat /proc/sys/kernel/tainted => page allocation failure: order:6

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Date:   Mon, 10 May 2021 13:19:38 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@...ia.com>
Cc:     "hch@....de" <hch@....de>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "rdna@...com" <rdna@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: cat /proc/sys/kernel/tainted => page allocation failure: order:6

On Mon, May 10, 2021 at 11:12:21AM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote:
> Hello,
> 
> Why is order 6 allocation required for "cat /proc/sys/kernel/tainted" ...?
> I'm seeing (occasional) failures in one VM (with 65d uptime):
> 
> [5674989.634561] cat: page allocation failure: order:6, mode:0x40dc0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO), nodemask=(null),cpuset=user.slice,mems_allowed=0
> [5674989.645432] CPU: 0 PID: 2717524 Comm: cat Not tainted 5.10.19-200.fc33.x86_64 #1

The underlying problem is that 'cat' is asking to do a 128kB read (!)
so we allocate 256kB (!) of contiguous (!) memory.  This is already
mostly fixed upstream.  Please upgrade your kernel.