On Fri, 20 Apr 2018, Matthew Wilcox wrote: > On Fri, Apr 20, 2018 at 04:54:53PM -0400, Mikulas Patocka wrote: > > On Fri, 20 Apr 2018, Michal Hocko wrote: > > > No way. This is just wrong! First of all, you will explode most likely > > > on many allocations of small sizes. Second, CONFIG_DEBUG_VM tends to be > > > enabled quite often. > > > > You're an evil person who doesn't want to fix bugs. > > Steady on. There's no need for that. Michal isn't evil. Please > apologise. I see this attitude from Michal again and again. He didn't want to fix vmalloc(GFP_NOIO), he didn't want to fix alloc_pages sleeping when __GFP_NORETRY is used. So what should I say? Fix them and you won't be evil :-) (he could also fix the oom killer, so that it is triggered when free_memory+cache+free_swap goes beyond a threshold and not when you loop too long in the allocator) > > You refused to fix vmalloc(GFP_NOIO) misbehavior a year ago (did you make > > some progress with it since that time?) and you refuse to fix kvmalloc > > misuses. > > I understand you're frustrated, but this is not the way to get the problems > fixed. > > > I tried this patch on text-only virtual machine and /proc/vmallocinfo > > shows 614kB more memory. I tried it on a desktop machine with the chrome > > browser open and /proc/vmallocinfo space is increased by 7MB. So no - this > > won't exhaust memory and kill the machine. > > This is good data, thank you for providing it. > > > Arguing that this increases memory consumption is as bogus as arguing that > > CONFIG_LOCKDEP increses memory consumption. No one is forcing you to > > enable CONFIG_LOCKDEP and no one is forcing you to enable this kvmalloc > > test too. > > I think there's a real problem which is that CONFIG_DEBUG_VM is too broad. > It inserts code in a *lot* of places, some of which is quite expensive. > We would do better to split it into more granular pieces ... although > an explosion of configuration options isn't great either. Maybe just > CONFIG_DEBUG_VM and CONFIG_DEBUG_VM_EXPENSIVE. > > Michal may be wrong, but he's not evil. I already said that we can change it from CONFIG_DEBUG_VM to CONFIG_DEBUG_SG - or to whatever other option you may want, just to make sure that it is enabled in distro debug kernels by default. Mikulas
