On Fri, Jul 31, 2020 at 01:38:34PM -0700, Andrew Morton wrote: > On Thu, 30 Jul 2020 16:12:05 -0700 "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote: > > > So, may we add a GFP_ flag that will cause kmalloc() and friends to return > > NULL when they would otherwise need to acquire their non-raw spinlock? > > This avoids adding any overhead to the slab-allocator fastpaths, but > > allows callback invocation to reduce cache misses without having to > > restructure some existing callers of call_rcu() and potential future > > callers of kfree_rcu(). > > We have eight free gfp_t bits so that isn't a problem. Whew!!! ;-) > Adding a test-n-branch to the kmalloc() fastpath may well be a concern. > > Which of mm/sl?b.c are affected? None of them, it turns out. The initial patch will instead directly invoke __get_free_page(). So we could just leave sl?b.c alone. > A doesnt-need-to-really-work protopatch would help us understand the > potential cost? Makes sense! My guess is that Uladzislau Rezki (CCed) will be sending one along by the middle of next week. Thanx, Paul
