On Tue, Jan 25, 2022 at 06:46:35PM +0000, Matthew Wilcox wrote: > On Tue, Jan 25, 2022 at 06:12:48PM +0100, Uladzislau Rezki wrote: > > On Tue, Jan 25, 2022 at 04:50:14PM +0000, Matthew Wilcox wrote: > > > On Tue, Jan 25, 2022 at 05:39:12PM +0100, Uladzislau Rezki (Sony) wrote: > > > > @@ -1768,7 +1776,8 @@ static void free_vmap_area_noflush(struct vmap_area *va) > > > > > > > > /* After this point, we may free va at any time */ > > > > if (unlikely(nr_lazy > lazy_max_pages())) > > > > - try_purge_vmap_area_lazy(); > > > > + if (!atomic_xchg(&drain_vmap_work_in_progress, 1)) > > > > + schedule_work(&drain_vmap_work); > > > > } > > > > > > Is it necessary to have drain_vmap_work_in_progress? The documentation > > > says: > > > > > > * This puts a job in the kernel-global workqueue if it was not already > > > * queued and leaves it in the same position on the kernel-global > > > * workqueue otherwise. > > > > > > and the implementation seems to use test_and_set_bit() to ensure this > > > is true. > > > > > It checks pending state, if the work is in run-queue you can place it > > one more time. The motivation of having it is to prevent the drain work > > of being placed several times at once what i see on my stress testing. > > > > CPU_1: invokes vfree() -> queues the drain work -> TASK_RUNNING > > CPU_2: invokes vfree() -> queues the drain work one more time since it was not pending > > But why not unconditionally call schedule_work() here? > We can :) The question is do we agree that extra queuing will be kind of spurious? Because the CPU_1 will complete all cleanups once it is physically on CPU and others workers just bail out. We can disregard those spurious wake-ups for sure. If someone complains about it in the future we can think later then. Re-spin and do it unconditionally? I do not have a strong opinion about it. -- Vlad Rezki
