linux-kernel - Re: [PATCH v4] xen: speed up grant-table reclaim

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Date:   Thu, 27 Jul 2023 07:30:42 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc:     Xen developer discussion <xen-devel@...ts.xenproject.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v4] xen: speed up grant-table reclaim

On 26.07.23 18:52, 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 via a module parameter.
> 
> 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>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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