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    SubjectRe: [PATCH 06/10] x86: reduce memory and stack usage in intel_cacheinfo
    Ingo Molnar wrote:
    > * Mike Travis <travis@sgi.com> 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


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