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

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Message-ID: <20130828212358.GF1357@kmo-pixel>
Date:	Wed, 28 Aug 2013 14:26:34 -0700
From:	Kent Overstreet <kmo@...erainc.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Aug 28, 2013 at 02:10:19PM -0700, Andrew Morton wrote:
> 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.

Ok... and I could see how the fact that it currently _doesn't_ have
anything to do with the existing code would be confusing...

Do you think that if/when it's making use of the ida rewrite it'll be
ok? Or would you still prefer to have it in a new file (and if so, any
preference on the naming?)
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