linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+55aFxmseHugpuNMqFxiz8r86PPwth=Fd-U-_wC8_E-kDP3hA@mail.gmail.com>
Date:	Fri, 12 Dec 2014 16:44:49 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

On Fri, Dec 12, 2014 at 4:34 PM, Sasha Levin <sasha.levin@...cle.com> wrote:
>
> Right, it's virtio-9p. However, virtio-9p acts merely as a proxy to an underlying
> tmpfs - so while it's slow, I don't think it's way slower than the average disk
> backed ext4.

I was thinking more in the sense of "how much of the trouble is about
something like tmpfs eating tons of memory when trinity starts doing
random system calls on those files".

I was also thinking that some of it might be filesystem-specific. We
already *did* see one trace where it was in the loop getting virtio
channel data. Maybe it's actually possible to overwhelm the 9p
filesystem exactly because the backing store is tmpfs, and basically
have a CPU 100% busy handling ring events from the virtual
filesystem..

But I'm just flailing..

                     Linus
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