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

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Date:   Mon, 10 May 2021 12:43:58 +0000
From:   "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@...ia.com>
To:     "willy@...radead.org" <willy@...radead.org>
CC:     "hch@....de" <hch@....de>, "rdna@...com" <rdna@...com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "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, 2021-05-10 at 13:19 +0100, Matthew Wilcox wrote:
> On Mon, May 10, 2021 at 11:12:21AM +0000, Rantala, Tommi T. (Nokia -
> FI/Espoo) wrote:
> > 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.

Ahh, thanks!
Indeed I missed "proc: use kvzalloc for our kernel buffer"
-Tommi