Hi Catalin,
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).
I can't say I remember enough details from kmemleak to comment on the
locking complications you point out, though.
- Pekka
