Re: [PATCH] Revert "kmemleak: allow to coexist with fault injection"

[Michal Hocko <mhocko@kernel.org>]

On Tue 16-07-19 15:21:17, Qian Cai wrote:
[...]
> Thanks to this commit, there are allocation with __GFP_DIRECT_RECLAIM that
> succeeded would keep trying with __GFP_NOFAIL for kmemleak tracking object
> allocations.

Well, not really. Because low order allocations with
__GFP_DIRECT_RECLAIM basically never fail (they keep retrying) even
without GFP_NOFAIL because that flag is actually to guarantee no
failure. And for high order allocations the nofail mode is actively
harmful. It completely changes the behavior of a system. A light costly
order workload could put the system on knees and completely change the
behavior. I am not really convinced this is a good behavior of a
debugging feature TBH.

> Otherwise, one kmemleak object allocation failure would kill the
> whole kmemleak.

Which is not great but quite likely a better than an unpredictable MM
behavior caused by NOFAIL storms. Really, this NOFAIL patch is a
completely broken behavior. There shouldn't be much discussion about
reverting it. I would even argue it shouldn't have been merged in the
first place. It doesn't have any acks nor reviewed-bys while it abuses
__GFP_NOFAIL which is generally discouraged to be used.

Thanks!
-- 
Michal Hocko
SUSE Labs