On Wed, Jun 29, 2022 at 02:07:20PM -0700, Paul E. McKenney wrote: > On Wed, Jun 29, 2022 at 07:47:36PM +0000, Joel Fernandes wrote: > > On Wed, Jun 29, 2022 at 09:56:27AM -0700, Paul E. McKenney wrote: > > > On Tue, Jun 28, 2022 at 05:13:21PM -0400, Joel Fernandes wrote: > > > > On Tue, Jun 28, 2022 at 12:56 PM Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Mon, Jun 27, 2022 at 02:43:59PM -0700, Paul E. McKenney wrote: > > > > > > On Mon, Jun 27, 2022 at 09:18:13PM +0000, Joel Fernandes wrote: > > > > > > > On Mon, Jun 27, 2022 at 01:59:07PM -0700, Paul E. McKenney wrote: > > > > > > > > On Mon, Jun 27, 2022 at 08:56:43PM +0200, Uladzislau Rezki wrote: > > > > > > > > > > As per the comments in include/linux/shrinker.h, .count_objects callback > > > > > > > > > > should return the number of freeable items, but if there are no objects > > > > > > > > > > to free, SHRINK_EMPTY should be returned. The only time 0 is returned > > > > > > > > > > should be when we are unable to determine the number of objects, or the > > > > > > > > > > cache should be skipped for another reason. > > > > > > > > > > > > > > > > > > > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > > > > > > > > > --- > > > > > > > > > > kernel/rcu/tree.c | 2 +- > > > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > > > > > > index 711679d10cbb..935788e8d2d7 100644 > > > > > > > > > > --- a/kernel/rcu/tree.c > > > > > > > > > > +++ b/kernel/rcu/tree.c > > > > > > > > > > @@ -3722,7 +3722,7 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) > > > > > > > > > > atomic_set(&krcp->backoff_page_cache_fill, 1); > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > - return count; > > > > > > > > > > + return count == 0 ? SHRINK_EMPTY : count; > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > static unsigned long > > > > > > > > > > -- > > > > > > > > > > 2.37.0.rc0.104.g0611611a94-goog > > > > > > > > > > > > > > > > > > > Looks good to me! > > > > > > > > > > > > > > > > > > Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > > > > > > > > > > > > > > > Now that you mention it, this does look independent of the rest of > > > > > > > > the series. I have pulled it in with Uladzislau's Reviewed-by. > > > > > > > > > > > > > > Thanks Paul and Vlad! > > > > > > > > > > > > > > Paul, apologies for being quiet. I have been working on the series and the > > > > > > > review comments carefully. I appreciate your help with this work. > > > > > > > > > > > > Not a problem. After all, this stuff is changing some of the trickier > > > > > > parts of RCU. We must therefore assume that some significant time and > > > > > > effort will be required to get it right. > > > > > > > > > > To your point about trickier parts of RCU, the v2 series though I tested it > > > > > before submitting is now giving me strange results with rcuscale. Sometimes > > > > > laziness does not seem to be in effect (as pointed out by rcuscale), other > > > > > times I am seeing stalls. > > > > > > > > > > So I have to carefully look through all of this again. I am not sure why I > > > > > was not seeing these issues with the exact same code before (frustrated). > > > > > > > > Looks like I found at least 3 bugs in my v2 series which testing > > > > picked up now. RCU-lazy was being too lazy or not too lazy. Now tests > > > > pass, so its progress but does beg for more testing: > > > > > > It is entirely possible that call_rcu_lazy() needs its own special > > > purpose tests. This might be a separate test parallel to the test for > > > kfree_rcu() in kernel/rcu/rcuscale.c, for example. > > > > I see, perhaps I can add a 'lazy' flag to rcutorture as well, so it uses > > call_rcu_lazy() for its async RCU invocations? > > That will be tricky because of rcutorture's timeliness expectations. I have facility now to set the lazy timeout from test kernel modules. I was thinking I could set the same from rcu torture. Maybe something like a 100 jiffies? Then it can run through all the regular rcutorture tests and still exercise the new code paths. > Maybe a self-invoking lazy callback initiated by rcu_torture_fakewriter() > that prints a line about its statistics at shutdown time? At a minimum, > the number of times that it was invoked. Better would be to print one > line summarizing stats for all of them. > > The main thing that could be detected from this is a callback being > stranded. Given that rcutorture enqueues non-lazy callbacks like a > drunken sailor, they won't end up being all that lazy. Thanks for this idea as well. I'll think more about it. thanks, - Joel
