linux-kernel - Re: [PATCH v1 5/8] mm, kasan: Stackdepot implementation. Enable stackdepot for SLAB

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Date:	Mon, 1 Feb 2016 11:55:31 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Alexander Potapenko <glider@...gle.com>
Cc:	kasan-dev@...glegroups.com, Christoph Lameter <cl@...ux.com>,
	linux-kernel@...r.kernel.org, Dmitriy Vyukov <dvyukov@...gle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>, linux-mm@...ck.org,
	Andrey Konovalov <adech.fo@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, rostedt@...dmis.org
Subject: Re: [PATCH v1 5/8] mm, kasan: Stackdepot implementation. Enable
 stackdepot for SLAB

On Thu, Jan 28, 2016 at 02:27:44PM +0100, Alexander Potapenko wrote:
> On Thu, Jan 28, 2016 at 1:51 PM, Alexander Potapenko <glider@...gle.com> wrote:
> >
> > On Jan 28, 2016 8:40 AM, "Joonsoo Kim" <iamjoonsoo.kim@....com> wrote:
> >>
> >> Hello,
> >>
> >> On Wed, Jan 27, 2016 at 07:25:10PM +0100, Alexander Potapenko wrote:
> >> > Stack depot will allow KASAN store allocation/deallocation stack traces
> >> > for memory chunks. The stack traces are stored in a hash table and
> >> > referenced by handles which reside in the kasan_alloc_meta and
> >> > kasan_free_meta structures in the allocated memory chunks.
> >>
> >> Looks really nice!
> >>
> >> Could it be more generalized to be used by other feature that need to
> >> store stack trace such as tracepoint or page owner?
> > Certainly yes, but see below.
> >
> >> If it could be, there is one more requirement.
> >> I understand the fact that entry is never removed from depot makes things
> >> very simpler, but, for general usecases, it's better to use reference
> >> count
> >> and allow to remove. Is it possible?
> > For our use case reference counting is not really necessary, and it would
> > introduce unwanted contention.

Okay.

> > There are two possible options, each having its advantages and drawbacks: we
> > can let the clients store the refcounters directly in their stacks (more
> > universal, but harder to use for the clients), or keep the counters in the
> > depot but add an API that does not change them (easier for the clients, but
> > potentially error-prone).
> > I'd say it's better to actually find at least one more user for the stack
> > depot in order to understand the requirements, and refactor the code after
> > that.

I re-think the page owner case and it also may not need refcount.
For now, just moving this stuff to /lib would be helpful for other future user.

BTW, is there any performance number? I guess that it could affect
the performance.

Thanks.