Re: [patch 3/3] mm: fault handler to replace nopage and populate

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> The truncate logic can't be duplicated because it works on struct pages.
> 
> What sounds best, if you use nopfn, is to do your own internal
> synchronisation against your unmap call. Obviously you can't because you
> have no ->nopfn_done call with which to drop locks ;)
> 
> So, hmm yes I have a good idea for how fault() could take over ->nopfn as
> well: just return NULL, set the fault type to VM_FAULT_MINOR, and have
> the ->fault handler install the pte. It will require a new helper along
> the lines of vm_insert_page.
> 
> I'll code that up in my next patchset.

Which is exactly what I was proposing in my other mail :)

Read it, you'll understnad my point about the truncate logic... I
sometimes want to return struct page (when the mapping is pointing to
backup memory) or map it directly to hardware.

In the later case, with an appropriate helper, I can definitely do my
own locking. In the former case, I return struct page's and need the
truncate logic.

Ben.


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