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

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Date:	Tue, 01 Sep 2015 14:21:43 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Richard Yao <ryao@...too.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Brian Behlendorf <behlendorf@...l.gov>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Change global memory state symbols to GPL-only

On Tue, 2015-09-01 at 01:24 +0000, Richard Yao wrote:
> On Mon, 2015-08-17 09:56:55 -0700, Ben Hutchings wrote:
> > 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.
> 
> The idea of providing third party drivers with the hooks that they 
> need to
> respond to memory pressure is by no means Linux-specific. In 
> OpenSolaris, there
> are counters for drivers to keep track of memory usage and try to 
> stay ahead of
> it, which works because there is no direct reclaim. There are also 
> callbacks
> for the SLAB code to defragment the caches used by the drivers. 


So you confirm that the Linux and Solaris APIs for this are quite
different.

> Giving non-GPL
> drivers to respond to memory pressure seems reasonable.

I don't see why.

[...]
> > Yes, that's the idea, proprietary code should not be helped in this
> > way.
> 
> The ZFSOnLinux kernel driver uses these symbols. It is fully open 
> source and
> not proprietary.
[...]

It's not GPL-compatible, which in terms of Linux kernel modules is no
better than proprietary.

Ben.

-- 
Ben Hutchings
The first rule of tautology club is the first rule of tautology club.


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