> On Nov 17, 2022, at 7:58 AM, Uladzislau Rezki <urezki@xxxxxxxxx> wrote: > > 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. > Ah, ok. >> >> Also it still does cond_synchronize_rcu() :-( >> > Sometimes we need to wait for a GP we can not just release :) You know that is not what I meant ;) I was concerned about the blocking. Thanks, - Joel > > -- > Uladzislau Rezki
