> vmalloc() is, by design, not permitted to be used in atomic context and > already contains components which may sleep, so avoiding spin locks is not > a problem from the perspective of atomic context. > > The global vmap_area_lock is held when the red/black tree rooted in > vmap_are_root is accessed and thus is rather long-held and under > potentially high contention. It is likely to be under contention for reads > rather than write, so replace it with a rwsem. > > Each individual vmap_block->lock is likely to be held for less time but > under low contention, so a mutex is not an outrageous choice here. > > A subset of test_vmalloc.sh performance results:- > > fix_size_alloc_test 0.40% > full_fit_alloc_test 2.08% > long_busy_list_alloc_test 0.34% > random_size_alloc_test -0.25% > random_size_align_alloc_test 0.06% > ... > all tests cycles 0.2% > > This represents a tiny reduction in performance that sits barely above > noise. > How important to have many simultaneous users of vread()? I do not see a big reason to switch into mutexes due to performance impact and making it less atomic. So, how important for you to have this change? -- Uladzislau Rezki
