On Wed, Nov 16, 2022 at 10:05:46PM +0000, Joel Fernandes wrote: > On Wed, Nov 16, 2022 at 7:19 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote: > > > > Hello, Paul, Joel. > > > > > > > > > > Yes sure, I am doing a run now with my patch. However, I have a > > > > question -- why do you feel blocking in the kworker is not an issue? > > > > You are taking a snapshot before queuing the normal kwork and then > > > > reading the snapshot when the normal kwork runs. Considering it is a > > > > high priority queue, the delay between when you are taking the > > > > snapshot, and reading it is likely small so there is a bigger chance > > > > of blocking in cond_synchronize_rcu(). Did I miss something? > > > > > > > We can wait indeed in the reclaim worker. But the worker does not do any > > > nasty or extra work here. If there is a need we block and wait. After a > > > grace period, we are awoken and proceed. > > > > > > Therefore i do not see the reason in handling two cases: > > > > > > if (gp_done) > > > queue_work(); > > > else > > > queue_rcu_work(); > > > > > > it is the same if we just queue the work and check on entry. The current > > > scenario is: queue the work after a grace period. This is the difference. > > > > > > Right if the reclaimer was a high prio kthread a time would be shorter. > > > > > > In your scenario the time seems even shorter(i have not checked) because > > > you update a snapshot of krcp each time a kvfree_rcu() is invoked. So > > > basically even though you have objects whose grace period is passed you > > > do not separate it anyhow. Because you update the: > > > > > > krcp->gp_snap = get_state_synchronize_rcu(); > > > > > > too often. > > > > > Once upon a time we discussed that it is worth to keep track of GP > > per-a-page in order to reduce a memory footprint. Below patch addresses > > it: > > In the patch below, it appears you are tracking the GP per krwp, and > not per page. But I could be missing something - could you split it > into separate patches for easier review? > I will split. I was thinking about it. The GP is tracked per-a-page. As for krwp it is only for channel_3. Everything goes there if no-page or no cache. > > Also it still does cond_synchronize_rcu() :-( > Sometimes we need to wait for a GP we can not just release :) -- Uladzislau Rezki
