linux-kernel - Re: [PATCH] Percpu tag allocator

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Message-ID: <20130613215800.GB28664@moria.home.lan>
Date:	Thu, 13 Jun 2013 14:58:00 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Jens Axboe <axboe@...nel.dk>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] Percpu tag allocator

On Thu, Jun 13, 2013 at 02:50:09PM -0700, Tejun Heo wrote:
> (cc'ing Rafael and Oleg)
> 
> On Thu, Jun 13, 2013 at 02:14:25PM -0700, Kent Overstreet wrote:
> > Yeah, I think you're definitely right. (I only started reading up on the
> > freezer stuff yesterday, though).
> > 
> > Do you know offhand what existing (i.e. slab) allocators do? Whatever
> > they do should make sense for us.
> 
> I don't think the memory allocator does anything.  Memory allocations
> are guaranteed to make forward progress and everything should still be
> working while freezing, so it doesn't need to do anything special.  If
> the tag allocator is to be used only by kernel proper - say drivers,
> block layer, it shouldn't need to do anything special.  If it's
> directly exposed to userland via something like aio and the userland
> is involved in guaranteeing forward progress - ie. freeing of tags -
> then the allocator would need to be able to fail, I think.

That's a good point - as long as whatever is allocated is guaranteed to
be freed in bounded time, we should be fine.
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