From: Andrew Morton <akpm@linux-foundation.org>
To: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>, Andi Kleen <andi@firstfloor.org>,
kvm-devel <kvm@vger.kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
lkml <linux-kernel@vger.kernel.org>,
lf-virt <virtualization@lists.linux-foundation.org>,
target-devel <target-devel@vger.kernel.org>,
Christoph Lameter <cl@gentwo.org>,
Oleg Nesterov <oleg@redhat.com>, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH-v3 1/4] idr: Percpu ida
Date: Wed, 28 Aug 2013 13:50:42 -0700 [thread overview]
Message-ID: <20130828135042.9e460b27699b52bb4eb53d9e@linux-foundation.org> (raw)
In-Reply-To: <20130828204454.GC1357@kmo-pixel>
On Wed, 28 Aug 2013 13:44:54 -0700 Kent Overstreet <kmo@daterainc.com> wrote:
> > > > What guarantees that this wait will terminate?
> > >
> > > It seems fairly clear to me from the break statement a couple lines up;
> > > if we were passed __GFP_WAIT we terminate iff we succesfully allocated a
> > > tag. If we weren't passed __GFP_WAIT we never actually sleep.
> >
> > OK ;) Let me rephrase. What guarantees that a tag will become available?
> >
> > If what we have here is an open-coded __GFP_NOFAIL then that is
> > potentially problematic.
>
> It's the same semantics as a mempool, really - it'll succeed when a tag
> gets freed.
OK, that's reasonable if the code is being used to generate IO tags -
we expect the in-flight tags to eventually be returned.
But if a client of this code is using the allocator for something
totally different, there is no guarantee that the act of waiting will
result in any tags being returned.
(These are core design principles/constraints which should be
explicitly documented in a place where future readers will see them!)
next prev parent reply other threads:[~2013-08-28 20:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-16 23:09 [PATCH-v3 0/4] target/vhost-scsi: Add per-cpu ida tag pre-allocation for v3.12 Nicholas A. Bellinger
2013-08-16 23:09 ` [PATCH-v3 1/4] idr: Percpu ida Nicholas A. Bellinger
2013-08-20 21:31 ` Andrew Morton
2013-08-26 20:14 ` Kent Overstreet
2013-08-28 19:53 ` Kent Overstreet
2013-08-28 20:23 ` Andrew Morton
2013-08-28 20:44 ` Kent Overstreet
2013-08-28 20:50 ` Andrew Morton [this message]
2013-08-28 21:12 ` Kent Overstreet
2013-08-28 21:15 ` Andrew Morton
2013-08-28 19:55 ` [PATCH] percpu ida: Switch to cpumask_t, add some comments Kent Overstreet
2013-08-28 20:25 ` Andrew Morton
2013-08-28 21:00 ` Kent Overstreet
2013-08-28 21:10 ` Andrew Morton
2013-08-28 21:26 ` Kent Overstreet
2013-08-28 21:36 ` Andrew Morton
2013-08-31 3:10 ` Nicholas A. Bellinger
2013-08-21 18:25 ` [PATCH-v3 1/4] idr: Percpu ida Christoph Lameter
2013-08-26 20:23 ` Kent Overstreet
2013-08-16 23:09 ` [PATCH-v3 2/4] target: Add transport_init_session_tags using per-cpu ida Nicholas A. Bellinger
2013-08-16 23:09 ` [PATCH-v3 3/4] vhost/scsi: Convert to per-cpu ida_alloc + ida_free command map Nicholas A. Bellinger
2013-08-16 23:09 ` [PATCH-v3 4/4] vhost/scsi: Add pre-allocation for tv_cmd SGL + upages memory Nicholas A. Bellinger
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