From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47EA7633.1080909@goop.org> Date: Wed, 26 Mar 2008 09:13:39 -0700 From: Jeremy Fitzhardinge MIME-Version: 1.0 Subject: Re: [PATCH 06/10] x86: reduce memory and stack usage in intel_cacheinfo References: <20080325220650.835342000@polaris-admin.engr.sgi.com> <20080325220651.683748000@polaris-admin.engr.sgi.com> <20080326065023.GG18301@elte.hu> <47EA6EA3.1070609@sgi.com> In-Reply-To: <47EA6EA3.1070609@sgi.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Mike Travis Cc: Ingo Molnar , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen List-ID: Mike Travis wrote: > Ingo Molnar wrote: > >> * Mike Travis wrote: >> >> >>> * Change the following static arrays sized by NR_CPUS to >>> per_cpu data variables: >>> >>> _cpuid4_info *cpuid4_info[NR_CPUS]; >>> _index_kobject *index_kobject[NR_CPUS]; >>> kobject * cache_kobject[NR_CPUS]; >>> >>> * Remove the local NR_CPUS array with a kmalloc'd region in >>> show_shared_cpu_map(). >>> >> thanks Travis, i've applied this to x86.git. >> >> one observation: >> >> >>> static ssize_t show_shared_cpu_map(struct _cpuid4_info *this_leaf, char *buf) >>> { >>> - char mask_str[NR_CPUS]; >>> - cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map); >>> - return sprintf(buf, "%s\n", mask_str); >>> + int n = 0; >>> + int len = cpumask_scnprintf_len(nr_cpu_ids); >>> + char *mask_str = kmalloc(len, GFP_KERNEL); >>> + >>> + if (mask_str) { >>> + cpumask_scnprintf(mask_str, len, this_leaf->shared_cpu_map); >>> + n = sprintf(buf, "%s\n", mask_str); >>> + kfree(mask_str); >>> + } >>> + return n; >>> >> the other changes look good, but this one looks a bit ugly and complex. >> We basically want to sprintf shared_cpu_map into 'buf', but we do that >> by first allocating a temporary buffer, print a string into it, then >> print that string into another buffer ... >> >> this very much smells like an API bug in cpumask_scnprintf() - why dont >> you create a cpumask_scnprintf_ptr() API that takes a pointer to a >> cpumask? Then this change would become a trivial and much more readable: >> >> - char mask_str[NR_CPUS]; >> - cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map); >> - return sprintf(buf, "%s\n", mask_str); >> + return cpumask_scnprintf_ptr(buf, NR_CPUS, &this_leaf->shared_cpu_map); >> >> Ingo >> > > The main goal was to avoid allocating 4096 bytes when only 32 would do > (characters needed to represent nr_cpu_ids cpus instead of NR_CPUS cpus.) > But I'll look at cleaning it up a bit more. It wouldn't have to be > a function if CHUNKSZ in cpumask_scnprintf() were visible (or a non-changeable > constant.) > It's a pity you can't take advantage of kasprintf to handle all this. Hm, I would say that bitmap_scnprintf is a candidate for implementation as a printk format specifier so you could get away from needing a special function to print bitmaps... Eh? What's the difference between snprintf and scnprintf? J -- 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