From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47EA6EA3.1070609@sgi.com> Date: Wed, 26 Mar 2008 08:41:23 -0700 From: Mike Travis 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> In-Reply-To: <20080326065023.GG18301@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Ingo Molnar Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen List-ID: 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.) Thanks, Mike -- 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