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 ... Instead of drain_vmap_work_in_progress hack we can make use of work_busy() helper. The main concern with that was the comment around that function: /** * work_busy - test whether a work is currently pending or running * @work: the work to be tested * * Test whether @work is currently pending or running. There is no * synchronization around this function and the test result is * unreliable and only useful as advisory hints or for debugging. * * Return: * OR'd bitmask of WORK_BUSY_* bits. */ i am not sure how reliable this is. Thoughts? -- Vlad Rezki
