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McKenney" To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, byungchul.park@lge.com, Josh Triplett , Lai Jiangshan , linux-doc@vger.kernel.org, Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt , kernel-team@android.com Subject: Re: [PATCH 5/5] rcu: Remove kfree_call_rcu_nobatch() Message-ID: <20190828215636.GA26530@linux.ibm.com> Reply-To: paulmck@kernel.org References: <5d657e3b.1c69fb81.54250.01e2@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5d657e3b.1c69fb81.54250.01e2@mx.google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-28_11:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908280210 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Tue, Aug 27, 2019 at 03:01:59PM -0400, Joel Fernandes (Google) wrote: > Now that kfree_rcu() special casing have been removed from tree RCU, > remove kfree_call_rcu_nobatch() since it is not needed. > > Signed-off-by: Joel Fernandes (Google) Now -this- one qualifies as a nice negative delta! ;-) A few things below, please fix in next version. Thanx, Paul > --- > .../admin-guide/kernel-parameters.txt | 4 --- > include/linux/rcutiny.h | 5 --- > include/linux/rcutree.h | 1 - > kernel/rcu/rcuperf.c | 10 +----- > kernel/rcu/tree.c | 33 ++++++++----------- > 5 files changed, 14 insertions(+), 39 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 24fe8aefb12c..56be0e30100b 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3909,10 +3909,6 @@ > Number of loops doing rcuperf.kfree_alloc_num number > of allocations and frees. > > - rcuperf.kfree_no_batch= [KNL] > - Use the non-batching (less efficient) version of kfree_rcu(). > - This is useful for comparing with the batched version. > - > rcuperf.nreaders= [KNL] > Set number of RCU readers. The value -1 selects > N, where N is the number of CPUs. A value > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h > index 949841f52ec5..7aa93afa5d8d 100644 > --- a/include/linux/rcutiny.h > +++ b/include/linux/rcutiny.h > @@ -39,11 +39,6 @@ static inline void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > call_rcu(head, func); > } > > -static inline void kfree_call_rcu_nobatch(struct rcu_head *head, rcu_callback_t func) > -{ > - call_rcu(head, func); > -} > - > void rcu_qs(void); > > static inline void rcu_softirq_qs(void) > diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h > index 961b7e05d141..0b68aa952f8b 100644 > --- a/include/linux/rcutree.h > +++ b/include/linux/rcutree.h > @@ -34,7 +34,6 @@ static inline void rcu_virt_note_context_switch(int cpu) > > void synchronize_rcu_expedited(void); > void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func); > -void kfree_call_rcu_nobatch(struct rcu_head *head, rcu_callback_t func); > > void rcu_barrier(void); > bool rcu_eqs_special_set(int cpu); > diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c > index c1e25fd10f2a..da94b89cd531 100644 > --- a/kernel/rcu/rcuperf.c > +++ b/kernel/rcu/rcuperf.c > @@ -593,7 +593,6 @@ rcu_perf_shutdown(void *arg) > torture_param(int, kfree_nthreads, -1, "Number of threads running loops of kfree_rcu()."); > torture_param(int, kfree_alloc_num, 8000, "Number of allocations and frees done in an iteration."); > torture_param(int, kfree_loops, 10, "Number of loops doing kfree_alloc_num allocations and frees."); > -torture_param(int, kfree_no_batch, 0, "Use the non-batching (slower) version of kfree_rcu()."); > > static struct task_struct **kfree_reader_tasks; > static int kfree_nrealthreads; > @@ -632,14 +631,7 @@ kfree_perf_thread(void *arg) > if (!alloc_ptr) > return -ENOMEM; > > - if (!kfree_no_batch) { > - kfree_rcu(alloc_ptr, rh); > - } else { > - rcu_callback_t cb; > - > - cb = (rcu_callback_t)(unsigned long)offsetof(struct kfree_obj, rh); > - kfree_call_rcu_nobatch(&(alloc_ptr->rh), cb); > - } > + kfree_rcu(alloc_ptr, rh); > } > > cond_resched(); > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 12c17e10f2b4..c767973d62ac 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2777,8 +2777,10 @@ static void kfree_rcu_work(struct work_struct *work) > rcu_lock_acquire(&rcu_callback_map); > trace_rcu_invoke_kfree_callback(rcu_state.name, head, offset); > > - /* Could be possible to optimize with kfree_bulk in future */ > - kfree((void *)head - offset); > + if (!WARN_ON_ONCE(!__is_kfree_rcu_offset(offset))) { > + /* Could be optimized with kfree_bulk() in future. */ > + kfree((void *)head - offset); > + } This really needs to be in the previous patch until such time as Tiny RCU no longer needs the restriction. > rcu_lock_release(&rcu_callback_map); > cond_resched_tasks_rcu_qs(); > @@ -2856,16 +2858,6 @@ static void kfree_rcu_monitor(struct work_struct *work) > spin_unlock_irqrestore(&krcp->lock, flags); > } > > -/* > - * This version of kfree_call_rcu does not do batching of kfree_rcu() requests. > - * Used only by rcuperf torture test for comparison with kfree_rcu_batch(). > - */ > -void kfree_call_rcu_nobatch(struct rcu_head *head, rcu_callback_t func) > -{ > - __call_rcu(head, func); > -} > -EXPORT_SYMBOL_GPL(kfree_call_rcu_nobatch); > - > /* > * Queue a request for lazy invocation of kfree() after a grace period. > * > @@ -2885,12 +2877,6 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > unsigned long flags; > struct kfree_rcu_cpu *krcp; > > - /* kfree_call_rcu() batching requires timers to be up. If the scheduler > - * is not yet up, just skip batching and do the non-batched version. > - */ > - if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) > - return kfree_call_rcu_nobatch(head, func); > - > if (debug_rcu_head_queue(head)) { > /* Probable double kfree_rcu() */ > WARN_ONCE(1, "kfree_call_rcu(): Double-freed call. rcu_head %p\n", > @@ -2909,8 +2895,15 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > krcp->head = head; > > /* Schedule monitor for timely drain after KFREE_DRAIN_JIFFIES. */ > - if (!xchg(&krcp->monitor_todo, true)) > - schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); > + if (!xchg(&krcp->monitor_todo, true)) { > + /* Scheduling the monitor requires scheduler/timers to be up, > + * if it is not, just skip it. An eventual kfree_rcu() will > + * kick it again. > + */ > + if ((rcu_scheduler_active == RCU_SCHEDULER_RUNNING)) { > + schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); > + } > + } And this also needs to be in an earlier patch. Bisectability and all that! Are we really guaranteed that there will be an eventual kfree_rcu()? More of a worry for Tiny RCU than for Tree RCU, but still could be annoying for someone trying to debug a memory leak. Thanx, Paul > spin_unlock(&krcp->lock); > local_irq_restore(flags); > -- > 2.23.0.187.g17f5b7556c-goog >