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Date: Wed, 25 Jun 2014 16:09:32 +0400
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Attilio Rao <attilio@freebsd.org>
Subject: Re: svn commit: r267858 - in head/sys/dev: virtio/balloon xen/balloon
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On Wed, Jun 25, 2014 at 01:58:29PM +0200, Attilio Rao wrote:
A> > Log:
A> >   xen/virtio: fix balloon drivers to not mark pages as WIRED
A> >
A> >   Prevent the Xen and VirtIO balloon drivers from marking pages as
A> >   wired. This prevents them from increasing the system wired page count,
A> >   which can lead to mlock failing because of hitting the limit in
A> >   vm.max_wired.
A> 
A> This change is conceptually wrong.
A> The pages balloon is allocating are unmanaged and they should be wired
A> by definition. Alan and I are considering enforcing this (mandatory
A> wired pages for unmanaged pages allocation) directly in the KPI.
A> This in practice just seem an artifact to deal with scarce  wired
A> memory limit. I suggest that for the XEN case this limit gets bumped
A> rather relying on similar type of hacks.

Proper limit would be to count pages wired by userland via mlock(2)
and enforce limit only on those pages. Pages wired by kernel should
be either unlimited or controled by a separate limit.

-- 
Totus tuus, Glebius.