On Thu, Sep 30, 2021 at 11:56:12AM -0700, Suren Baghdasaryan wrote:

I thought more about these alternative suggestions for userspace to
record allocations but that would introduce considerable complexity
into userspace. Userspace would have to collect and consolidate this
data by some daemon, all users would have to query it for the data
(IPC or something similar), in case this daemon crashes the data would
need to be somehow recovered. So, in short, it's possible but makes
things much more complex compared to proposed in-kernel
implementation.

Agreed: this is something for the kernel to manage.

OTOH, the only downside of the current implementation is the
additional memory required to store anon vma names. I checked the
memory consumption on the latest Android with these patches and
because we share vma names during fork, the actual memory required to
store vma names is no more than 600kB. Even on older phones like Pixel
3 with 4GB RAM, this is less than 0.015% of total memory. IMHO, this
is an acceptable price to pay.

I think that's entirely fine. We don't end up with any GUP games, and
everything is refcounted.

I think a v10 with the various nits fixed would be a good next step
here. What do you think Matthew?

-- 
Kees Cook