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Date:   Thu, 30 Sep 2021 16:25:02 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
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Subject: Re: [PATCH v9 2/3] mm: add a field to store names for private
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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