From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx119.postini.com [74.125.245.119]) by kanga.kvack.org (Postfix) with SMTP id AF1DC6B0002 for ; Mon, 22 Apr 2013 19:15:20 -0400 (EDT) Message-ID: <1366672518.9609.142.camel@gandalf.local.home> Subject: Re: [PATCH] slab: Remove unnecessary __builtin_constant_p() From: Steven Rostedt Date: Mon, 22 Apr 2013 19:15:18 -0400 In-Reply-To: <20130422141621.384eb93a6a8f3d441cd1a991@linux-foundation.org> References: <1366225776.8817.28.camel@pippen.local.home> <20130422134415.32c7f2cac07c924bff3017a4@linux-foundation.org> <1366664301.9609.140.camel@gandalf.local.home> <20130422141621.384eb93a6a8f3d441cd1a991@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: David Rientjes , Pekka Enberg , LKML , linux-mm@kvack.org, Christoph Lameter , Behan Webster On Mon, 2013-04-22 at 14:16 -0700, Andrew Morton wrote: > On Mon, 22 Apr 2013 16:58:21 -0400 Steven Rostedt wrote: > > When looking into this, we found the only two users of the index_of() > > static function that has this issue, passes in size_of(), which will > > always be a constant, making the check redundant. > > Looking at the current callers is cheating. What happens if someone > adds another caller which doesn't use sizeof? Well, as it required a size of something, if it was dynamic then what would the size be of? > > > Note, this is a bug in Clang that will hopefully be fixed soon. But for > > now, this strange redundant compile time check is preventing Clang from > > even testing the Linux kernel build. > > > > > > And I still think the original change log has rational for the change, > > as it does make it rather confusing to what is happening there. > > The patch made index_of() weaker! > > It's probably all a bit academic, given that linux-next does > > -/* > - * This function must be completely optimized away if a constant is passed to > - * it. Mostly the same as what is in linux/slab.h except it returns an index. > - */ > -static __always_inline int index_of(const size_t size) > -{ > - extern void __bad_size(void); > - > - if (__builtin_constant_p(size)) { > - int i = 0; > - > -#define CACHE(x) \ > - if (size <=x) \ > - return i; \ > - else \ > - i++; > -#include > -#undef CACHE > - __bad_size(); > - } else > - __bad_size(); > - return 0; > -} > - Looks like someone just ate the bird. -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org