From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 26 Mar 2008 18:12:41 +0100 From: Ingo Molnar Subject: Re: [PATCH 06/10] x86: reduce memory and stack usage in intel_cacheinfo Message-ID: <20080326171241.GC20016@elte.hu> References: <20080325220650.835342000@polaris-admin.engr.sgi.com> <20080325220651.683748000@polaris-admin.engr.sgi.com> <20080326065023.GG18301@elte.hu> <47EA6EA3.1070609@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47EA6EA3.1070609@sgi.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Mike Travis Cc: 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: > >> + 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.) well, do we care about allocating 4096 bytes, as long as we also free it? It's not like we need to clear all the bytes or something. Am i missing something here? Ingo -- 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