Re: Allow migration of mlocked pages

[Hugh Dickins <hugh@veritas.com>]

On Wed, 24 May 2006, Christoph Lameter wrote:
> On Wed, 24 May 2006, Hugh Dickins wrote:
> 
> > Oh, I'm not worried about whether ordinary VM_LOCKED pages will get
> > migrated properly, I can't see any problem with that.  It's whether
> > something somewhere is using mlock and somehow relying on the
> > physical pages to be pinned.  I don't know what form that "somehow"
> > would take, and I'm not saying there is or can be any such thing:
> > just worried that we want wide exposure yet few testers migrate.
> 
> All of these driver mappings are installed using remap_pfn_page. These are 
> mappings that are not considered by page migration at all because:

Misunderstanding again.  I've no worries about those drivers
you've supplied a patch for, what you've done there is surely okay.

I'm (slightly) worried there's some app out there that's been using
mlock to pin physical pages.  My worry may be senseless: how can
physical pages mean anything to it without a driver in the kernel
to cooperate in the assumption?

If it were a big worry, I wouldn't have sent you in this
"migrate VM_LOCKED" direction at all.  I'm all for it, just
cautioning that we want a period of exposure to varied testing.

Hugh

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