linux-kernel - Re: [PATCH-v4 1/6] idr: Percpu ida

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Date:	Tue, 27 Aug 2013 13:58:38 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	target-devel <target-devel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, Asias He <asias@...hat.com>,
	Kent Overstreet <kmo@...erainc.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-v4 1/6] idr: Percpu ida

On Tue, 2013-08-27 at 13:43 -0700, Andrew Morton wrote:
> On Tue, 27 Aug 2013 20:11:41 +0000 "Nicholas A. Bellinger" <nab@...ux-iscsi.org> wrote:
> 
> > Percpu frontend for allocating ids. With percpu allocation (that works),
> > it's impossible to guarantee it will always be possible to allocate all
> > nr_tags - typically, some will be stuck on a remote percpu freelist
> > where the current job can't get to them.
> > 
> > We do guarantee that it will always be possible to allocate at least
> > (nr_tags / 2) tags - this is done by keeping track of which and how many
> > cpus have tags on their percpu freelists. On allocation failure if
> > enough cpus have tags that there could potentially be (nr_tags / 2) tags
> > stuck on remote percpu freelists, we then pick a remote cpu at random to
> > steal from.
> > 
> > Note that there's no cpu hotplug notifier - we don't care, because
> > steal_tags() will eventually get the down cpu's tags. We _could_ satisfy
> > more allocations if we had a notifier - but we'll still meet our
> > guarantees and it's absolutely not a correctness issue, so I don't think
> > it's worth the extra code.
> 
> Except for one silly trivial thing, all of my August 20 review comments
> were ignored.  You didn't even bother replying to the email.
> 

Sorry, unfortunately this email didn't make it through Kent's email
filter last week, and he responded to the thread yesterday.

Kent, can you address Andrew's remaining comments please..?

--nab

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