On Fri, Mar 26, 2021 at 07:03:47PM +0200, Andy Shevchenko wrote: > The bitmap.h header is used in a lot of code around the kernel. > Besides that it includes kernel.h which sometimes makes a loop.
How much of the kernel does *not* end up pulling kernel.h anyway, making all subsequent includes fast no-ops? Realistically, any C compiler is going to recognize the case when included file has contents of form #ifndef <pp-id> #define <pp-id> <possibly empty sequence of preprocessor tokens> <lines> #endif where <lines> contain no exposed #else, #elif or #endif and remember that subsequent includes of that file should be ignored unless <pp-id> becomes undefined. AFAICS, on e.g. allmodconfig amd64 build it's (at most - there might've been false positives) 131 files out of ~30000; on defconfig it's 55 out of ~2300. How much does your patch change that?
