On Tue, 21 Jun 2016 02:33:06 +0300 Yury Norov <yury.norov@xxxxxxxxx> wrote: > kmalloc_index() uses simple straightforward way to calculate > bit position of nearest or equal upper power of 2. > This effectively results in generation of 24 episodes of > compare-branch instructions in assembler. > > There is shorter way to calculate this: fls(size - 1). > > The patch removes hard-coded calculation of kmalloc slab and > uses ilog2() instead that works on top of fls(). ilog2 is used > with intention that compiler also might optimize constant case > during compile time if it detects that. > > BUG() is moved to the beginning of function. We left it here to > provide identical behaviour to previous version. It may be removed > if there's no requirement in it anymore. > > While we're at this, fix comment that describes return value. kmalloc_index() is always called with a constant-valued `size' (see __builtin_constant_p() tests) so the compiler will evaluate the switch statement at compile-time. This will be more efficient than calling fls() at runtime. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>