linux-kernel - Re: [PATCH] percpu ida: Switch to cpumask

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Message-Id: <20130828141019.25aff643c87e43ffafdbcb7e@linux-foundation.org>
Date:	Wed, 28 Aug 2013 14:10:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	target-devel <target-devel@...r.kernel.org>,
	lf-virt <virtualization@...ts.linux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	kvm-devel <kvm@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, Asias He <asias@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <cl@...two.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] percpu ida: Switch to cpumask_t, add some comments

On Wed, 28 Aug 2013 14:00:10 -0700 Kent Overstreet <kmo@...erainc.com> wrote:

> On Wed, Aug 28, 2013 at 01:25:50PM -0700, Andrew Morton wrote:
> > On Wed, 28 Aug 2013 12:55:17 -0700 Kent Overstreet <kmo@...erainc.com> wrote:
> > 
> > > Fixup patch, addressing Andrew's review feedback:
> > 
> > Looks reasonable.
> > 
> > >  lib/idr.c           | 38 +++++++++++++++++++++-----------------
> > 
> > I still don't think it should be in this file.
> > 
> > You say that some as-yet-unmerged patches will tie the new code into
> > the old ida code.  But will it do it in a manner which requires that
> > the two reside in the same file?
> 
> Not require, no - but it's just intimate enough with my ida rewrite that
> I think it makes sense; it makes some use of stuff that should be
> internal to the ida code.
> 
> Mostly just sharing the lock though, since I got rid of the ida
> interfaces that don't do locking, but percpu ida needs a lock that also
> covers what ida needs.
> 
> It also makes use of a ganged allocation interface, but there's no real
> reason ida can't expose that, it's just unlikely to be useful to
> anything but percpu ida.
> 
> The other reason I think it makes sense to live in idr.c is more for
> users of the code; as you pointed out as far as the user's perspective
> percpu ida isn't doing anything fundamentally different from ida, so I
> think it makes sense for the code to live in the same place as a
> kindness to future kernel developers who are trying to find their way
> around the various library code.

I found things to be quite the opposite - it took 5 minutes of staring,
head-scratching, double-checking and penny-dropping before I was
confident that the newly-added code actually has nothing at all to do
with the current code.  Putting it in the same file was misleading, and
I got misled.
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