On 1/13/21 5:09 PM, Johannes Berg wrote: > From: Johannes Berg <[email protected]> > > If kmemleak is enabled, it uses a kmem cache for its own objects. > These objects are used to hold information kmemleak uses, including > a stack trace. If slub_debug is also turned on, each of them has > *another* stack trace, so the overhead adds up, and on my tests (on > ARCH=um, admittedly) 2/3rds of the allocations end up being doing > the stack tracing. > > Turn off SLAB_STORE_USER if SLAB_NOLEAKTRACE was given, to avoid > storing the essentially same data twice. > > Signed-off-by: Johannes Berg <[email protected]>
How about stripping away SLAB_STORE_USER only if it's added from the global slub_debug variable? In case somebody lists one of the kmemleak caches explicitly in "slub_debug=..." instead of just booting with "slub_debug", we should honor that. > --- > Perhaps instead it should go the other way around, and kmemleak > could even use/access the stack trace that's already in there ... > But I don't really care too much, I can just turn off slub debug > for the kmemleak caches via the command line anyway :-) > > --- > mm/slub.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 34dcc09e2ec9..625a32a6645b 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1446,7 +1446,16 @@ slab_flags_t kmem_cache_flags(unsigned int object_size, > } > } > > - return flags | slub_debug; > + flags |= slub_debug; > + > + /* > + * If the slab cache is for debugging (e.g. kmemleak) then > + * don't store user (stack trace) information. > + */ > + if (flags & SLAB_NOLEAKTRACE) > + flags &= ~SLAB_STORE_USER; > + > + return flags; > } > #else /* !CONFIG_SLUB_DEBUG */ > static inline void setup_object_debug(struct kmem_cache *s, >
