From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Knutsson Date: Fri, 16 Feb 2007 17:36:57 +0000 Subject: Re: [KJ] [PATCH] is_power_of_2 in ia64mm Message-Id: <45D5EBB9.4080903@student.ltu.se> List-Id: References: <1171627435.6127.0.camel@wriver-t81fb058.linuxcoe> <45D5C789.1090607@student.ltu.se> <45D5D47F.3000303@student.ltu.se> <45D5DE6F.6030604@student.ltu.se> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Robert P. J. Day" Cc: Andreas Schwab , linux-mm@kvack.org, tony.luck@intel.com, linux-ia64@vger.kernel.org, Kernel Janitors List , linux-kernel@vger.kernel.org Robert P. J. Day wrote: > i'm not clear on what the possible problem is here: > > On Fri, 16 Feb 2007, Richard Knutsson wrote: > > >> Andreas Schwab wrote: >> >>> Richard Knutsson writes: >>> >>> >>>> Andreas Schwab wrote: >>>> >>>> >>>>> Richard Knutsson writes: >>>>> >>>>> >>>>> >>>>>> Vignesh Babu BM wrote: >>>>>> >>>>>> >>>>>>> @@ -175,7 +176,7 @@ static int __init hugetlb_setup_sz(char *str) >>>>>>> tr_pages = 0x15557000UL; >>>>>>> size = memparse(str, &str); >>>>>>> - if (*str || (size & (size-1)) || !(tr_pages & size) || >>>>>>> + if (*str || !is_power_of_2(size) || !(tr_pages & size) || >>>>>>> size <= PAGE_SIZE || >>>>>>> size >= (1UL << PAGE_SHIFT << MAX_ORDER)) { >>>>>>> printk(KERN_WARNING "Invalid huge page size specified\n"); >>>>>>> >>>>>>> >>>>>> As we talked about before; is this really correct? !is_power_of_2(0) = >>>>>> true while (0 & (0-1)) = 0. >>>>>> >>>>>> >>>>> size = 0 is also covered by the next two conditions, so the overall value >>>>> does not change. >>>>> >>>>> >>>> Yes, but is it meant to state that 'size' is not a power of two? >>>> >>>> >>> What else can it mean? >>> >> What about !one_or_less_bit()? It has not been implemented (yet?) >> but been discussed. >> > > but whether or not it's been implemented doesn't change whether or not > the code above can be simplified. given what's being tested, and the > error message about whether a page size is valid, it seems fairly > clear that this is a power of two test. what's the problem? > Fsck, I can't see that. But if that is what's intended, well then... (5 min later) Ok, now I think I see it. Sorry for the noise.. > >> It ended by concluding that is_power_of_2() should be fixed up first >> and then we can see about it. >> > > there's nothing about is_power_of_2() that needs "fixing". it's > correct as it's currently implemented. > Oh, I didn't mean that is_power_of_2() need to be fixed, I meant fixing/replacing the kernel with is_power_of_2(). Todays lesson: don't try to code while you have a cold... Richard Knutsson