Re: [Qemu-devel] [PATCH 00/10] RFC: userfault

[Dave Hansen]

On 07/02/2014 09:50 AM, Andrea Arcangeli wrote:
> The MADV_USERFAULT feature should be generic enough that it can
> provide the userfaults to the Android volatile range feature too, on
> access of reclaimed volatile pages.

Maybe.

I certainly can't keep track of all the versions of the variations of
the volatile ranges patches.  But, I don't think it's a given that this
can be reused.  First of all, volatile ranges is trying to replace
ashmem and is going to require _some_ form of sharing.  This mechanism,
being tightly coupled to anonymous memory at the moment, is not a close
fit for that.

It's also important to call out that this is a VMA-based mechanism.  I
certainly can't predict what we'll merge for volatile ranges, but not
all of them are VMA-based.  We'd also need a mechanism on top of this to
differentiate plain not-present pages from not-present-because-purged pages.

That said, I _think_ this might fit well in to what the Mozilla guys
wanted out of volatile ranges.  I'm not confident about it, though.