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 ePKfjsHd t8PaQiCT360x2kogRh3kY8E9V7q0L3jnhDggKWuASB/4WTAt3zb7cg021jQalZNuHNr7pTjqdRJeErCutg8p7N1SVRrR8GisQ8nYI3VTzoZ0/1dJoTikbKK3a/B6jhzk9AECCMFnN8FHxKTB1EODMuYigdj/yo6dKl/7pZMEYp+JRcZllk61S9k1w3FSSb3TCM+0b9VESReenzaujoxzNz+s7wpft3tlytqFL/eBpkuDd+c1KGjTxVkBT9VXhNfBvFO4poYM3hI+/1xrD/8F8sZYcXwdDqeYeuwoHvcdpBBbu0oB7IrO18FA7W67Q1Pxbq0OPaPVzvnJCFZiUjKX82lFgnY1/5j9ECKZvk0lhm/WNtbWzjM4eGSRPtwpSvHnxu5EhlMVq77QGEJQyLGXoTVVNl1S7DfrB8reFcUX1UH643vqw9lZDOaxGLg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/7/2026 1:37 PM, Gustavo Luiz Duarte wrote: > There is currently no easy way to monitor how many RCU callbacks are > pending system-wide. The existing trace points provide per-event data > but require active tracing, which makes them awkward for fleet-wide > monitoring. Knowing the depth and stage of pending callbacks helps > admins reason about RCU health, gives an indirect signal of memory > held back by RCU, and is useful when tuning RCU parameters. > > This series adds a debugfs file at: > > /sys/kernel/debug/rcu/pending_cbs > > that reports per-CPU pending callback counts with a "total" row. > > Patch 1 introduces the file with per-CPU columns for each segcblist > segment (done, wait, next_ready, next) plus a "lazy" column. > > Patch 2 extends the file with a "kfree_rcu" column reporting objects > queued in the batched kfree_rcu()/kvfree_rcu() path > (CONFIG_KVFREE_RCU_BATCHED), which has its own per-CPU queues outside > the main segmented callback list. > > Signed-off-by: Gustavo Luiz Duarte You actually don't need debugfs for this. You can just use bpftrace and instrument trace_rcu_ (with other RCU tracing Kconfig options enabled?). I had something like that working sometime ago. Generally RCU doesn't add userspace interfaces randomly like that. I remember Paul ripped similar things out some time ago.