On Tue, Sep 08, 2020 at 09:42:45AM +0300, Mike Rapoport wrote: > On Sun, Sep 06, 2020 at 06:06:39PM +0200, Mateusz Nosek wrote: > > Hi, > > > > I performed simple benchmarks using custom kernel module with the code > > fragment in question 'copy-pasted' in there in both versions. In case of 1k, > > 10k and 100k iterations the average time for kzalloc version was 5.1 and for > > kmalloc 3.9, for each iterations number. > > The time was measured using 'ktime_get(void)' function and the results given > > here are in ktime_t units. > > The machine I use has 4 core Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz CPU. > > > > The performance increase happens, but as you wrote it is probably not really > > noticeable. > > I don't think that saving a few cylces of memset() in a function that > called only on the initialization path in very particular cases is worth > risking uninitialized variables when somebody will add a new field to > the 'struct mmu_notifier_subscriptions' and will forget to explicitly > set it. Indeed, it is not a common path, it is already very expensive if code is running here (eg it does mm_take_all_locks()). So there is no reason at all to optimize this and risk problems down the road. Jason
