From: Catalin Marinas <catalin.marinas@arm.com>
To: Pekka Enberg <penberg@iki.fi>
Cc: Qian Cai <cai@lca.pw>,
akpm@linux-foundation.org, cl@linux.com, mhocko@kernel.org,
willy@infradead.org, penberg@kernel.org, rientjes@google.com,
iamjoonsoo.kim@lge.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation
Date: Thu, 28 Mar 2019 15:28:50 +0000 [thread overview]
Message-ID: <20190328152850.GE10283@arrakis.emea.arm.com> (raw)
In-Reply-To: <8e88b618-e774-de81-ca99-a8ee89f60b5a@iki.fi>
On Thu, Mar 28, 2019 at 01:50:29PM +0200, Pekka Enberg wrote:
> On 27/03/2019 2.59, Qian Cai wrote:
> > > > Unless there is a brave soul to reimplement the kmemleak to embed it's
> > > > metadata into the tracked memory itself in a foreseeable future, this
> > > > provides a good balance between enabling kmemleak in a low-memory
> > > > situation and not introducing too much hackiness into the existing
> > > > code for now.
>
> On Thu, Mar 28, 2019 at 08:05:31AM +0200, Pekka Enberg wrote:
> > > Unfortunately I am not that brave soul, but I'm wondering what the
> > > complication here is? It shouldn't be too hard to teach calculate_sizes() in
> > > SLUB about a new SLAB_KMEMLEAK flag that reserves spaces for the metadata.
>
> On 28/03/2019 12.30, Catalin Marinas wrote:> I don't think it's the
> calculate_sizes() that's the hard part. The way
> > kmemleak is designed assumes that the metadata has a longer lifespan
> > than the slab object it is tracking (and refcounted via
> > get_object/put_object()). We'd have to replace some of the
> > rcu_read_(un)lock() regions with a full kmemleak_lock together with a
> > few more tweaks to allow the release of kmemleak_lock during memory
> > scanning (which can take minutes; so it needs to be safe w.r.t. metadata
> > freeing, currently relying on a deferred RCU freeing).
>
> Right.
>
> I think SLUB already supports delaying object freeing because of KASAN (see
> the slab_free_freelist_hook() function) so the issue with metadata outliving
> object is solvable (although will consume more memory).
Thanks. That's definitely an area to investigate.
> I can't say I remember enough details from kmemleak to comment on the
> locking complications you point out, though.
They are not too bad, I'd just need some quiet couple of days to go
through them (which I don't have at the moment).
--
Catalin
prev parent reply other threads:[~2019-03-28 15:28 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 0:59 [PATCH v4] kmemleak: survive in a low-memory situation Qian Cai
2019-03-27 8:44 ` Michal Hocko
2019-03-27 11:34 ` Qian Cai
2019-03-27 11:44 ` Michal Hocko
2019-03-27 13:05 ` Qian Cai
2019-03-27 13:17 ` Michal Hocko
2019-03-27 17:29 ` Catalin Marinas
2019-03-27 18:02 ` Qian Cai
2019-03-28 15:05 ` Catalin Marinas
2019-03-28 15:41 ` Qian Cai
2019-03-27 18:17 ` Michal Hocko
2019-03-27 18:21 ` Matthew Wilcox
2019-03-28 14:59 ` Catalin Marinas
2019-03-28 15:24 ` Qian Cai
2019-03-29 12:02 ` Michal Hocko
2019-03-29 16:16 ` Catalin Marinas
2019-04-01 20:12 ` Michal Hocko
2019-04-05 16:43 ` Catalin Marinas
2019-03-28 6:05 ` Pekka Enberg
2019-03-28 10:30 ` Catalin Marinas
2019-03-28 11:50 ` Pekka Enberg
2019-03-28 15:28 ` Catalin Marinas [this message]
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