From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Uladzislau Rezki (Sony)" <urezki@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 09/17] rcu/tree: cache specified number of objects
Date: Wed, 24 Jun 2020 13:12:18 -0700 [thread overview]
Message-ID: <20200624201226.21197-9-paulmck@kernel.org> (raw)
In-Reply-To: <20200624201200.GA28901@paulmck-ThinkPad-P72>
From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
In order to reduce the dynamic need for pages in kfree_rcu(),
pre-allocate a configurable number of pages per CPU and link
them in a list. When kfree_rcu() reclaims objects, the object's
container page is cached into a list instead of being released
to the low-level page allocator.
Such an approach provides O(1) access to free pages while also
reducing the number of requests to the page allocator. It also
makes the kfree_rcu() code to have free pages available during
a low memory condition.
A read-only sysfs parameter (rcu_min_cached_objs) reflects the
minimum number of allowed cached pages per CPU.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 8 +++
kernel/rcu/tree.c | 66 +++++++++++++++++++++++--
2 files changed, 70 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb95fad..befaa63 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4038,6 +4038,14 @@
latencies, which will choose a value aligned
with the appropriate hardware boundaries.
+ rcutree.rcu_min_cached_objs= [KNL]
+ Minimum number of objects which are cached and
+ maintained per one CPU. Object size is equal
+ to PAGE_SIZE. The cache allows to reduce the
+ pressure to page allocator, also it makes the
+ whole algorithm to behave better in low memory
+ condition.
+
rcutree.jiffies_till_first_fqs= [KNL]
Set delay from grace-period initialization to
first attempt to force quiescent states.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4fba1e9..f767a37 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -175,6 +175,15 @@ module_param(gp_init_delay, int, 0444);
static int gp_cleanup_delay;
module_param(gp_cleanup_delay, int, 0444);
+/*
+ * This rcu parameter is runtime-read-only. It reflects
+ * a minimum allowed number of objects which can be cached
+ * per-CPU. Object size is equal to one page. This value
+ * can be changed at boot time.
+ */
+static int rcu_min_cached_objs = 2;
+module_param(rcu_min_cached_objs, int, 0444);
+
/* Retrieve RCU kthreads priority for rcutorture */
int rcu_get_gp_kthreads_prio(void)
{
@@ -2979,7 +2988,6 @@ struct kfree_rcu_cpu_work {
* struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
* @head: List of kfree_rcu() objects not yet waiting for a grace period
* @bhead: Bulk-List of kfree_rcu() objects not yet waiting for a grace period
- * @bcached: Keeps at most one object for later reuse when build chain blocks
* @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
* @lock: Synchronize access to this structure
* @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
@@ -2995,13 +3003,22 @@ struct kfree_rcu_cpu_work {
struct kfree_rcu_cpu {
struct rcu_head *head;
struct kfree_rcu_bulk_data *bhead;
- struct kfree_rcu_bulk_data *bcached;
struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
raw_spinlock_t lock;
struct delayed_work monitor_work;
bool monitor_todo;
bool initialized;
int count;
+
+ /*
+ * A simple cache list that contains objects for
+ * reuse purpose. In order to save some per-cpu
+ * space the list is singular. Even though it is
+ * lockless an access has to be protected by the
+ * per-cpu lock.
+ */
+ struct llist_head bkvcache;
+ int nr_bkv_objs;
};
static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
@@ -3038,6 +3055,31 @@ krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
local_irq_restore(flags);
}
+static inline struct kfree_rcu_bulk_data *
+get_cached_bnode(struct kfree_rcu_cpu *krcp)
+{
+ if (!krcp->nr_bkv_objs)
+ return NULL;
+
+ krcp->nr_bkv_objs--;
+ return (struct kfree_rcu_bulk_data *)
+ llist_del_first(&krcp->bkvcache);
+}
+
+static inline bool
+put_cached_bnode(struct kfree_rcu_cpu *krcp,
+ struct kfree_rcu_bulk_data *bnode)
+{
+ // Check the limit.
+ if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
+ return false;
+
+ llist_add((struct llist_node *) bnode, &krcp->bkvcache);
+ krcp->nr_bkv_objs++;
+ return true;
+
+}
+
/*
* This function is invoked in workqueue context after a grace period.
* It frees all the objects queued on ->bhead_free or ->head_free.
@@ -3073,7 +3115,12 @@ static void kfree_rcu_work(struct work_struct *work)
kfree_bulk(bhead->nr_records, bhead->records);
rcu_lock_release(&rcu_callback_map);
- if (cmpxchg(&krcp->bcached, NULL, bhead))
+ krcp = krc_this_cpu_lock(&flags);
+ if (put_cached_bnode(krcp, bhead))
+ bhead = NULL;
+ krc_this_cpu_unlock(krcp, flags);
+
+ if (bhead)
free_page((unsigned long) bhead);
cond_resched_tasks_rcu_qs();
@@ -3206,7 +3253,7 @@ kfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp,
/* Check if a new block is required. */
if (!krcp->bhead ||
krcp->bhead->nr_records == KFREE_BULK_MAX_ENTR) {
- bnode = xchg(&krcp->bcached, NULL);
+ bnode = get_cached_bnode(krcp);
if (!bnode) {
WARN_ON_ONCE(sizeof(struct kfree_rcu_bulk_data) > PAGE_SIZE);
@@ -4259,12 +4306,23 @@ static void __init kfree_rcu_batch_init(void)
for_each_possible_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+ struct kfree_rcu_bulk_data *bnode;
for (i = 0; i < KFREE_N_BATCHES; i++) {
INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
krcp->krw_arr[i].krcp = krcp;
}
+ for (i = 0; i < rcu_min_cached_objs; i++) {
+ bnode = (struct kfree_rcu_bulk_data *)
+ __get_free_page(GFP_NOWAIT | __GFP_NOWARN);
+
+ if (bnode)
+ put_cached_bnode(krcp, bnode);
+ else
+ pr_err("Failed to preallocate for %d CPU!\n", cpu);
+ }
+
INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
krcp->initialized = true;
}
--
2.9.5
next prev parent reply other threads:[~2020-06-24 20:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 20:12 [PATCH tip/core/rcu 0/17] kfree_rcu updates for v5.9 Paul E. McKenney
2020-06-24 20:12 ` [PATCH tip/core/rcu 01/17] rcu: Fix a kernel-doc warnings for "count" paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 02/17] rcu/tree: Keep kfree_rcu() awake during lock contention paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 03/17] rcu/tree: Skip entry into the page allocator for PREEMPT_RT paulmck
2020-06-30 16:45 ` Sebastian Andrzej Siewior
2020-06-30 18:35 ` Paul E. McKenney
2020-07-02 14:12 ` Sebastian Andrzej Siewior
2020-07-02 16:48 ` Paul E. McKenney
2020-07-02 20:19 ` Sebastian Andrzej Siewior
2020-07-06 21:06 ` Paul E. McKenney
2020-07-07 17:34 ` Uladzislau Rezki
2020-07-07 18:45 ` Joel Fernandes
2020-07-08 18:48 ` Uladzislau Rezki
2020-07-02 19:45 ` Uladzislau Rezki
2020-07-06 19:42 ` Joel Fernandes
2020-07-06 19:55 ` Uladzislau Rezki
2020-07-06 20:29 ` Joel Fernandes
2020-07-07 9:27 ` Sebastian Andrzej Siewior
2020-07-15 13:38 ` Uladzislau Rezki
2020-07-15 14:16 ` Sebastian Andrzej Siewior
2020-07-15 14:20 ` Uladzislau Rezki
2020-06-24 20:12 ` [PATCH tip/core/rcu 04/17] rcu/tree: Repeat the monitor if any free channel is busy paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 05/17] rcu/tree: Make debug_objects logic independent of rcu_head paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 06/17] rcu/tree: Simplify KFREE_BULK_MAX_ENTR macro paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 07/17] rcu/tree: Move kfree_rcu_cpu locking/unlocking to separate functions paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 08/17] rcu/tree: Use static initializer for krc.lock paulmck
2020-06-24 20:12 ` paulmck [this message]
2020-06-24 20:12 ` [PATCH tip/core/rcu 10/17] rcu/tree: Maintain separate array for vmalloc ptrs paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 11/17] rcu/tiny: support vmalloc in tiny-RCU paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 12/17] rcu: Rename *_kfree_callback/*_kfree_rcu_offset/kfree_call_* paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 13/17] mm/list_lru.c: Rename kvfree_rcu() to local variant paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 14/17] rcu: Introduce 2 arg kvfree_rcu() interface paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 15/17] rcu: Support reclaim for head-less object paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 16/17] rcu: Introduce single argument kvfree_rcu() interface paulmck
2020-06-24 20:12 ` [PATCH tip/core/rcu 17/17] lib/test_vmalloc.c: Add test cases for kvfree_rcu() paulmck
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