On 17.12.2019 12:31, Michal Hocko wrote: > On Mon 16-12-19 20:25:08, Waiman Long wrote: > [...] >> Both the hugetbl_lock and the subpool lock can be acquired in >> free_huge_page(). One way to solve the problem is to make both locks >> irq-safe. > > Please document why we do not take this, quite natural path and instead > we have to come up with an elaborate way instead. I believe the primary > motivation is that some operations under those locks are quite > expensive. Please add that to the changelog and ideally to the code as > well. We probably want to fix those anyway and then this would be a > temporary workaround. > >> Another alternative is to defer the freeing to a workqueue job. >> >> This patch implements the deferred freeing by adding a >> free_hpage_workfn() work function to do the actual freeing. The >> free_huge_page() call in a non-task context saves the page to be freed >> in the hpage_freelist linked list in a lockless manner. > > Do we need to over complicate this (presumably) rare event by a lockless > algorithm? Why cannot we use a dedicated spin lock for for the linked > list manipulation? This should be really a trivial code without an > additional burden of all the lockless subtleties. Why not llist_add()/llist_del_all() ?
