On Tue, 27 Feb 2018 05:06:43 -0800 Matthew Wilcox <wi...@infradead.org> wrote:
> On Tue, Feb 27, 2018 at 11:22:59AM +0100, Uladzislau Rezki (Sony) wrote: > > During finding a suitable hole in the vmap_area_list > > there is an explicit rescheduling check for latency reduction. > > We do it, since there are workloads which are sensitive for > > long (more than 1 millisecond) preemption off scenario. > > I understand your problem, but this is a horrid solution. If it takes > us a millisecond to find a suitable chunk of free address space, something > is terribly wrong. On a 3GHz CPU, that's 3 million clock ticks! Yup. > I think our real problem is that we have no data structure that stores > free VA space. We have the vmap_area which stores allocated space, but no > data structure to store free space. I wonder if we can reuse free_vmap_cache as a quick fix: if need_resched(), point free_vmap_cache at the current rb_node, drop the lock, cond_resched, goto retry?