linux-kernel - Re: [PATCH] mm: Change global memory state symbols to GPL-only

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Date:	Mon, 17 Aug 2015 18:51:27 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Change global memory state symbols to GPL-only

On Mon, 2015-08-17 at 17:11 +0200, Michal Hocko wrote:
> On Mon 17-08-15 16:56:32, Ben Hutchings wrote:
> > On Mon, 2015-08-17 at 15:54 +0200, Michal Hocko wrote:
> > > On Sun 16-08-15 01:42:27, Ben Hutchings wrote:
> > > > Proprietary modules should not be able to touch vm_stat or participate
> > > > in shrinking.
> > > 
> > > How does the external and !GPL fs does slab reclaim? Those are essential
> > > for the proper memory balancing.
> > 
> > If they know how to do shrinking on Linux then they are probably
> > derivative works of Linux.
> 
> I am not sure I understand. They are shrinking their internal cached
> objects and that is hardly a derivative work. The shrinker API is only
> meant to let them know _when_ this should happen and the interface is
> a pretty much simple callback API.

It is a Linux-specific API and I don't think other kernels provide
something similar to loadable modules.  It enables a module to turn a
large part of the system RAM into a cache and have the MM effectively
tell it the correct size of that cache, thus tightly integrating with
global memory management.

It seemed to me that this met the test for 'should this be
EXPORT_SYMBOL_GPL'.

> I do not want to defend a proprietary code here but this sounds like an
> obstruction for those modules which will lead into a worse code in the
> end because they should somehow manage the cache and it is much better
> when the core (MM) tells them when it makes sense rather than external
> heuristics.

Yes, that's the idea, proprietary code should not be helped in this
way.

Ben.

-- 
Ben Hutchings
[W]e found...that it wasn't as easy to get programs right as we had thought.
... I realized that a large part of my life from then on was going to be spent
in finding mistakes in my own programs. - Maurice Wilkes, 1949


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