On Tuesday 21 October 2008 04:03:37 Mike Travis wrote: > When nr_cpu_ids is set to CONFIG_NR_CPUS then references to nr_cpu_ids > will return the maximum index of the configured NR_CPUS (+1) instead > of the maximum index of the possible number of cpus (+1). This results > in extra unused memory being allocated by functions that are setting up > arrays of structs to keep track of per cpu items. 1) I like the name in this context: it's a beacon of sanity after NR_CPUS and nr_cpu_ids. But it's not so clearly a win when general code uses it: if (cpumask_first(mymask) == nr_cpumask_bits) ... vs: if (cpumask_first(mymask) == nr_cpu_ids) ... 2) This breaks anyone who tests that the iterators etc. return == nr_cpu_ids. One of the other patches tried to change them from NR_CPUS to nr_cpu_ids, that should now be revisited & reaudited. 3) Noone should be naively allocating "* nr_cpu_ids" arrays, they should be using per-cpu pointers. Not doing so wastes memory on non-contiguous processor systems. 4) It should be a constant not be dependent on CONFIG_CPUMASK_OFFSTACK, but rather as it was on NR_CPUS > BITS_PER_LONG. I think that's the sweet spot, and should also make your 2MB "gain" vanish. That's why I suggested a max_possible_cpu() function, and using that for those who really want to do allocations, who should be audited anyway, see (3). I don't want it as prominent as nr_cpu_ids, which is usually the Right Thing, and always safe. Cheers, Rusty. PS. I have part of a patch for this... -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
