@@ -5264,6 +5264,13 @@
number avoids disturbing real-time workloads,
but lengthens grace periods.
+ rcupdate.rcu_task_lazy_lim= [KNL]
+ Number of callbacks on a given CPU that will
+ cancel laziness on that CPU. Use -1 to disable
+ cancellation of laziness, but be advised that
+ doing so increases the danger of OOM due to
+ callback flooding.
+
rcupdate.rcu_task_stall_info= [KNL]
Set initial timeout in jiffies for RCU task stall
informational messages, which give some indication
@@ -176,6 +176,8 @@ static int rcu_task_contend_lim __read_mostly = 100;
module_param(rcu_task_contend_lim, int, 0444);
static int rcu_task_collapse_lim __read_mostly = 10;
module_param(rcu_task_collapse_lim, int, 0444);
+static int rcu_task_lazy_lim __read_mostly = 32;
+module_param(rcu_task_lazy_lim, int, 0444);
/* RCU tasks grace-period state for debugging. */
#define RTGS_INIT 0
@@ -354,8 +356,9 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
cblist_init_generic(rtp);
raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
}
- needwake = func == wakeme_after_rcu;
- if (havekthread && !timer_pending(&rtpcp->lazy_timer)) {
+ needwake = (func == wakeme_after_rcu) ||
+ (rcu_segcblist_n_cbs(&rtpcp->cblist) == rcu_task_lazy_lim);
+ if (havekthread && !needwake && !timer_pending(&rtpcp->lazy_timer)) {
if (rtp->lazy_jiffies)
mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp));
else
The various RCU Tasks flavors now do lazy grace periods when there are only asynchronous grace period requests. By default, the system will let 250 milliseconds elapse after the first call_rcu_tasks*() callbacki is queued before starting a grace period. In contrast, synchronous grace period requests such as synchronize_rcu_tasks*() will start a grace period immediately. However, invoking one of the call_rcu_tasks*() functions in a too-tight loop can result in a callback flood, which in turn can exhaust memory if grace periods are delayed for too long. This commit therefore sets a limit so that the grace-period kthread will be awakened when any CPU's callback list expands to contain rcupdate.rcu_task_lazy_lim callbacks elements (defaulting to 32, set to -1 to disable), the grace-period kthread will be awakened, thus cancelling any ongoing laziness and getting out in front of the potential callback flood. Cc: Alexei Starovoitov <ast@kernel.org> Cc: Martin KaFai Lau <kafai@fb.com> Cc: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ kernel/rcu/tasks.h | 7 +++++-- 2 files changed, 12 insertions(+), 2 deletions(-)