Hi Johannes, On 3/5/20 4:09 PM, Johannes Weiner wrote: > On Thu, Mar 05, 2020 at 09:49:23AM +0000, Vincenzo Frascino wrote: >> Hi Michal, >> >> On 3/4/20 4:53 PM, Michal Hocko wrote: >>> On Wed 04-03-20 14:23:48, Vincenzo Frascino wrote: >>>> mem_cgroup_id_get_many() is currently used only when MMU or MEMCG_SWAP >>>> configuration options are enabled. Having them disabled triggers the >>>> following warning at compile time: >>>> >>>> linux/mm/memcontrol.c:4797:13: warning: ‘mem_cgroup_id_get_many’ defined >>>> but not used [-Wunused-function] >>>> static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned >>>> int n) >>>> >>>> Make mem_cgroup_id_get_many() dependent on MMU and MEMCG_SWAP to address >>>> the issue. >>> >>> A similar patch has been proposed recently >>> http://lkml.kernel.org/r/87fthjh2ib.wl-kuninori.morimoto.gx@xxxxxxxxxxx. >>> The conclusion was that the warning is not really worth adding code. >>> >> >> Thank you for pointing this out, I was not aware of it. I understand that you >> are against "#ifdeffery" in this case, but isn't it the case of adding at least >> __maybe_unused? This would prevent people from reporting it over and over again >> and you to have to push them back :) Let me know what do you think, in case I am >> happy to change my patch accordingly. > > I would ack a patch that adds __maybe_unused. > > This is a tiny function. If we keep it around a few releases after > removing the last user, it costs us absolutely nothing. Eventually > somebody will notice and send a patch to remove it. No big deal. > > There is, however, real cost in keeping bogus warnings around and > telling people to ignore them. It's actively lowering the > signal-to-noise ratio and normalizing warnings to developers. That's > the kind of thing that will actually hide problems in the kernel. > > We know that the function can be unused in certain scenarios. It's > silly to let the compiler continue to warn about it. That's exactly > what __maybe_unused is for, so let's use it here. > I agree with what you are saying. I am going to change my patch accordingly. Thank you. -- Regards, Vincenzo
