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Date:   Wed, 7 Aug 2019 13:04:02 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
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        Ingo Molnar <mingo@redhat.com>, joelaf@google.com,
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        linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
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        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH v5 1/6] mm/page_idle: Add per-pid idle page tracking
 using virtual index
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On Wed,  7 Aug 2019 13:15:54 -0400 "Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:

> In Android, we are using this for the heap profiler (heapprofd) which
> profiles and pin points code paths which allocates and leaves memory
> idle for long periods of time. This method solves the security issue
> with userspace learning the PFN, and while at it is also shown to yield
> better results than the pagemap lookup, the theory being that the window
> where the address space can change is reduced by eliminating the
> intermediate pagemap look up stage. In virtual address indexing, the
> process's mmap_sem is held for the duration of the access.

So is heapprofd a developer-only thing?  Is heapprofd included in
end-user android loads?  If not then, again, wouldn't it be better to
make the feature Kconfigurable so that Android developers can enable it
during development then disable it for production kernels?