linux-kernel - Re: [PATCH v3] xen: speed up grant-table reclaim

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Message-ID: <ZKRFrtHQ0Gll0IpY@itl-email>
Date:   Tue, 4 Jul 2023 12:15:40 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Xen developer discussion <xen-devel@...ts.xenproject.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v3] xen: speed up grant-table reclaim

On Tue, Jul 04, 2023 at 02:07:47PM +0200, Jan Beulich wrote:
> On 27.06.2023 19:22, Demi Marie Obenour wrote:
> > When a grant entry is still in use by the remote domain, Linux must put
> > it on a deferred list.  Normally, this list is very short, because
> > the PV network and block protocols expect the backend to unmap the grant
> > first.  However, Qubes OS's GUI protocol is subject to the constraints
> > of the X Window System, and as such winds up with the frontend unmapping
> > the window first.  As a result, the list can grow very large, resulting
> > in a massive memory leak and eventual VM freeze.
> > 
> > To partially solve this problem, make the number of entries that the VM
> > will attempt to free at each iteration tunable.  The default is still
> > 10, but it can be overridden at compile-time (via Kconfig), boot-time
> > (via a kernel command-line option), or runtime (via sysfs).
> > 
> > This is Cc: stable because (when combined with appropriate userspace
> > changes) it fixes a severe performance and stability problem for Qubes
> > OS users.
> > 
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> 
> Why am I _still_ - after two earlier private questions to the same
> effect - on the To: list of this submission? Please can you respect
> other people's time and interests and properly follow patch
> submission rules, applying common sense when (like has been the
> case in the past for Linux) those rules result in overly broad sets
> of people.
> 
> Jan

Sorry, I somehow had that in an old version of the patch, and was
editing the patch by hand rather than generating it with git
format-patch.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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