On Wed 01-06-16 20:16:17, Peter Zijlstra wrote:
> On Wed, Jun 01, 2016 at 03:17:58PM +0200, Michal Hocko wrote:
> > Thanks Dave for your detailed explanation again! Peter do you have any
> > other idea how to deal with these situations other than opt out from
> > lockdep reclaim machinery?
> >
> > If not I would rather go with an annotation than a gfp flag to be honest
> > but if you absolutely hate that approach then I will try to check wheter
> > a CONFIG_LOCKDEP GFP_FOO doesn't break something else. Otherwise I would
> > steal the description from Dave's email and repost my patch.
> >
> > I plan to repost my scope gfp patches in few days and it would be good
> > to have some mechanism to drop those GFP_NOFS to paper over lockdep
> > false positives for that.
>
> Right; sorry I got side-tracked in other things again.
>
> So my favourite is the dedicated GFP flag, but if that's unpalatable for
> the mm folks then something like the below might work. It should be
> similar in effect to your proposal, except its more limited in scope.
[...]
> @@ -2876,11 +2883,36 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
> if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
> return;
>
> + /*
> + * Skip _one_ allocation as per the lockdep_skip_alloc() request.
> + * Must be done last so that we don't loose the annotation for
> + * GFP_ATOMIC like things from IRQ or other nesting contexts.
> + */
> + if (current->lockdep_reclaim_gfp & __GFP_SKIP_ALLOC) {
> + current->lockdep_reclaim_gfp &= ~__GFP_SKIP_ALLOC;
> + return;
> + }
> +
> mark_held_locks(curr, RECLAIM_FS);
> }
I might be missing something but does this work actually? Say you would
want a kmalloc(size), it would call
slab_alloc_node
slab_pre_alloc_hook
lockdep_trace_alloc
[...]
____cache_alloc_node
cache_grow_begin
kmem_getpages
__alloc_pages_node
__alloc_pages_nodemask
lockdep_trace_alloc
I understand your concerns about the scope but usually all allocations
have to be __GFP_NOFS or none in the same scope so I would see it as a
huge deal.
--
Michal Hocko
SUSE Labs
_______________________________________________
xfs mailing list
xfs@xxxxxxxxxxx
http://oss.sgi.com/mailman/listinfo/xfs
