On Sat, 31 Aug 2019, Matthew Wilcox wrote: > > The current behavior without special alignment for these caches has been > > in the wild for over a decade. And this is now coming up? > > In the wild ... and rarely enabled. When it is enabled, it may or may > not be noticed as data corruption, or tripping other debugging asserts. > Users then turn off the rare debugging option. Its enabled in all full debug session as far as I know. Fedora for example has been running this for ages to find breakage in device drivers etc etc. > > If there is an exceptional alignment requirement then that needs to be > > communicated to the allocator. A special flag or create a special > > kmem_cache or something. > > The only way I'd agree to that is if we deliberately misalign every > allocation that doesn't have this special flag set. Because right now, > breakage happens everywhere when these debug options are enabled, and > the very people who need to be helped are being hurt by the debugging. That is customarily occurring for testing by adding "slub_debug" to the kernel commandline (or adding debug kernel options) and since my information is that this is done frequently (and has been for over a decade now) I am having a hard time believing the stories of great breakage here. These drivers were not tested with debugging on before? Never ran with a debug kernel?
