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SubjectRe: [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem)
On Wed, 20 Feb 2008, Nick Piggin wrote:

> I don't know how this is supposed to solve anything. The sleeping
> problem happens I guess mostly in truncate. And all you are doing
> is putting these rmap callbacks in page_mkclean and try_to_unmap.

truncate is handled by the range invalidates. This is special code to deal
with the unnap/clean of an individual page.

> That doesn't seem right. To start with, the new callbacks aren't
> even called in the places where invalidate_page isn't allowed to
> sleep.
>
> The problem is unmap_mapping_range, right? And unmap_mapping_range
> must walk the rmaps with the mmap lock held, which is why it can't
> sleep. And it can't hold any mmap_sem so it cannot prevent address

Nope. unmap_mapping_range is already handled by the range callbacks.

> So in the meantime, you could have eg. a fault come in and set up a
> new page for one of the processes, and that page might even get
> exported via the same external driver. And now you have a totally
> inconsistent view.

The situation that you are imagining has already been dealt with by the
earlier patches. This is only to allow sleeping while unmapping individual
pages.


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