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Date:   Wed, 7 Aug 2019 13:58:40 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Joel Fernandes <joel@joelfernandes.org>
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Subject: Re: [PATCH v5 1/6] mm/page_idle: Add per-pid idle page tracking
 using virtual index
Message-Id: <20190807135840.92b852e980a9593fe91fbf59@linux-foundation.org>
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On Wed, 7 Aug 2019 16:45:30 -0400 Joel Fernandes <joel@joelfernandes.org> wrote:

> On Wed, Aug 07, 2019 at 01:04:02PM -0700, Andrew Morton wrote:
> > 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?
> 
> Almost all of this code is already configurable with
> CONFIG_IDLE_PAGE_TRACKING. If you disable it, then all of this code gets
> disabled.
> 
> Or are you referring to something else that needs to be made configurable?

Yes - the 300+ lines of code which this patchset adds!

The impacted people will be those who use the existing
idle-page-tracking feature but who will not use the new feature.  I
guess we can assume this set is small...