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a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=6IFa9wvqVegA:10 a=GoEa3M9JfhUA:10 a=MSJSkyAJlKp7O0UAvdIA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjA2MDEwMCBTYWx0ZWRfXzMRJefRxxyfh N/blydEhIXH4vKvHqIHpU/kxcg8RDrn5g6uqDjoO50wii2OPfJep4v9y9SGQmDsvlcAGFimDQBN syvYq2mziMcl2LLRzixWKpnoCQDjpeNKJiyOlU4X2GGWtp/H7OL9pL1venUquhHuBacxmJgpyxj 2bzsnr0uzl2KjsEU+gMl+Wagvbw7brZdF/EL/yj/Lw/i+j7q63FJ3PKqz0ilxagRT3MoqRCn9tA 7ya1Co9iPpSAL9N1SxiOTWAM4ityc2tQoth+Zfb3HfGtrF3VaDARMEz6BcH2U9dh8BvPnZ2If99 7UUA9rjieHSGaK4fW7rT6z19pBK7h4RAakOAl/6qoWrTdqeYc6zx7LX1TDlZWjYggRlF03Jwn9/ 4Z/C9t4A0acDI/XZ+Ygu0528f4N+MJtKmRHq5ILSgxaql3fntp15ZzMSxnf8bShYE4s6eTmo X-Proofpoint-ORIG-GUID: gSpujZKzEcmNoKXCcflr2yJFmXE-0oS9 X-Proofpoint-GUID: gSpujZKzEcmNoKXCcflr2yJFmXE-0oS9 On Fri, Jun 06, 2025 at 12:28:28PM +0200, David Hildenbrand wrote: > On 06.06.25 12:19, Lorenzo Stoakes wrote: > > On Fri, Jun 06, 2025 at 12:13:27PM +0200, Michal Hocko wrote: > > > On Fri 06-06-25 11:01:18, David Hildenbrand wrote: > > > > On 06.06.25 10:31, Michal Hocko wrote: > > > [...] > > > > > Turning them into VM_WARN_ON > > > > > should be reasonably safe as they are not enabled in production > > > > > environment anyway so we cannot really rely on those. Having them in > > > > > WARN form would be still useful for debugging and those that really need > > > > > a crash dump while debugging can achieve the same result. > > > > > > > > One question is if we should be VM_WARN_ON vs. VM_WARN_ON_ONCE ... > > > > > > *WARN_ONCE ha a very limited use from code paths which are generally > > > shared by many callers. You just see one and then nothing. Some time ago > > > we have discussed an option to have _ONCE per call trace but I haven't > > > see any follow up. > > > > > > Anyway starting without _ONCE seems like safer option because we are not > > > losing potentially useful debugging information. Afterall this is > > > debugging only thing. But no strong position on my side. > > > > > > > VM_BUG_ON is essentially a "once" thing so far, but then, we don't continue > > > > ... so probably most should be _ONCE. > > > > > > > > > > > > > > So while I agree that many of them could be dropped or made more clear > > > > > those could be dealt with after a mass move. An advantage of this would > > > > > be that we can drop VM_BUG_ON* and stop new instances from being added. > > > > > > > > As a first step we could probably just #define them to go to the > > > > VM_WARN_ON_* variants and see what happens. > > > > > > You meand VM_BUG_ON expand to VM_WARN_ON by default? > > > > Sorry to interject in the conversation, but to boldly throw my two English pence > > into the mix: > > > > As the "king of churn" (TM) you'll not be surprised to hear that I'm in favour > > of us just doing a big patch and convert all VM_BUG_ON() -> VM_WARN_ON_ONCE() > > and remove VM_BUG_ON*(). > > > > Pull the band-aid off... I think better than a #define if this indeed what you > > meant David. > > > > But of course, you'd expect me to have this opinion ;) > > See my reply to Michal regarding keeping VM_BUG_ON() until we actually > decided what the right cleanup is. Sure, but to me the concept of VM_BUG_ON() is surely fundamentally broken - if BUG_ON() means 'stop everything we're going to corrupt' then it makes no sense to add a '...but only if CONFIG_DEBUG_VM is set' in there. So to me the only assessment needed is 'do we want to warn on this or not?'. And as you say, really WARN_ON_ONCE() seems appropriate, because nearly always we will get flooded with useless information. I think this being debug code gives us a lot of leeway here. After the big change, we can always revisit individual cases and see if the warning is valid at all. > > I don't have a very strong opinion on any of this ... as long as VM_BUG_ON() > goes away one way or the other. Am happy to come up with the churn-meister version of this patch and take the heat :P > > -- > Cheers, > > David / dhildenb > Cheers, Lorenzo