linux-kernel - Re: linux-next: build failure after merge of the akpm-current tree

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Date:	Sat, 25 Jul 2015 14:24:02 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: linux-next: build failure after merge of the akpm-current tree

On Sat, 2015-07-25 at 12:47 -0700, Josh Triplett wrote:
> I certainly agree that it doesn't make sense to make all architectures
> select SRCU, if an unremovable core kernel feature uses SRCU.  If
> possible, I'd really like to avoid seeing SRCU become mandatory again,
> though.

I find it very strange that srcu is not taken for granted like rcu is,
or even regular locking primitives. How much overhead does srcu add?

> Is there any chance at all of the shrinker mechanism becoming optional?
> At first glance, it seems reasonably separate from the rest of mm, in
> that if it didn't exist and shrinking didn't happen, the rest of mm
> still works.  If that happened, MM_SHRINKER could select SRCU.

Some mm functionality might very possibly rely on srcu in the future if
we expect any chances of scaling, ie: faults. So I'd rather not take a
short term solution here, as we'll probably be discussing this again
otherwise.

> If that's not possible, then for the moment, I'd suggest making a hidden
> symbol MM_SHRINKER that's always y and does "select SRCU", to preserve
> SRCU's modularity for the moment while not forcing every architecture to
> select it.

This is _very_ hacking. While tinyfication has its uses and
applications, I'd rather not have it in the way of normal kernels.

Thanks,
Davidlohr

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