On Mon, 2015-02-02 at 11:13 -0800, Linus Torvalds wrote: > IOW, instead of > > m = 1UL << (BITS_PER_LONG - 2); > > perhaps something like > > m = 1UL << (BITS_PER_LONG/2- 2); > if (m < x) > m <<= BITS_PER_LONG/2; > > (assuming gcc can change that code into a "cmov") might cut down the > "lots of empty loops" case in half for small values of 'x'.
Makes a lot of sense. > There's probably some other better cheap initial guess value estimator. Just to get a feeling for the normal arg range in the non-driver parts that use this thing: fs/ceph/super.h: congestion_kb = (16*int_sqrt(totalram_pages)) << (PAGE_SHIFT-10); fs/nfs/write.c: nfs_congestion_kb = (16*int_sqrt(totalram_pages)) << (PAGE_SHIFT-10); fs/nfsd/nfscache.c: limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10); kernel/rcu/tree_plugin.h: ls = int_sqrt(nr_cpu_ids); mm/memcontrol.c: inactive_ratio = int_sqrt(10 * gb); mm/page_alloc.c: ratio = int_sqrt(10 * gb); mm/page_alloc.c: new_min_free_kbytes = int_sqrt(lowmem_kbytes * 16); So mostly values that scale according to mem or cpu. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
