From b18def121f077857ccf92fc620366e19850bc297 Mon Sep 17 00:00:00 2001 From: Yury Norov Date: Tue, 20 Apr 2021 20:13:25 -0700 Subject: bitmap_parse: Support 'all' semantics RCU code supports an 'all' group as a special case when parsing rcu_nocbs parameter. This patch moves the 'all' support to the core bitmap_parse code, so that all bitmap users can enjoy this extension. Moving 'all' parsing to a bitmap_parse level also allows users to pass patterns together with 'all' in regular group:pattern format, for example, "rcu_nocbs=all:1/2" would offload all the even-numbered CPUs regardless of the number of CPUs on the system. Reviewed-by: Andy Shevchenko Signed-off-by: Yury Norov Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-parameters.rst | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'Documentation') diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst index 3996b54158bf..01ba293a2d70 100644 --- a/Documentation/admin-guide/kernel-parameters.rst +++ b/Documentation/admin-guide/kernel-parameters.rst @@ -76,6 +76,11 @@ to change, such as less cores in the CPU list, then N and any ranges using N will also change. Use the same on a small 4 core system, and "16-N" becomes "16-3" and now the same boot input will be flagged as invalid (start > end). +The special case-tolerant group name "all" has a meaning of selecting all CPUs, +so that "nohz_full=all" is the equivalent of "nohz_full=0-N". + +The semantics of "N" and "all" is supported on a level of bitmaps and holds for +all users of bitmap_parse(). This document may not be entirely up to date and comprehensive. The command "modinfo -p ${modulename}" shows a current list of all parameters of a loadable -- cgit v1.2.3-58-ga151 From 18389c4570211e10e94f4a2ce907d01397abc335 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 19 Mar 2021 16:30:15 -0700 Subject: doc: Fix statement of RCU's memory-ordering requirements The sentence defining the relationship of accesses before a grace period to read-side accesses following that same grace period was missing a small word: "not". This commit therefore adds it. Reported-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst index a648b423ba0e..3f6ce41ee0c5 100644 --- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst +++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst @@ -21,7 +21,7 @@ Any code that happens after the end of a given RCU grace period is guaranteed to see the effects of all accesses prior to the beginning of that grace period that are within RCU read-side critical sections. Similarly, any code that happens before the beginning of a given RCU grace -period is guaranteed to see the effects of all accesses following the end +period is guaranteed to not see the effects of all accesses following the end of that grace period that are within RCU read-side critical sections. Note well that RCU-sched read-side critical sections include any region -- cgit v1.2.3-58-ga151 From 58d0db869d7ab8ca97b521f167022caa2c42cbe7 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Sun, 4 Apr 2021 23:58:43 +0200 Subject: doc: Fix diagram references in memory-ordering document The three diagrams describing rcu_gp_init() all spuriously refer to the same figure, probably due to a copy/paste issue. This commit fixes these references. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst index 3f6ce41ee0c5..11cdab037bff 100644 --- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst +++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst @@ -339,14 +339,14 @@ The diagram below shows the path of ordering if the leftmost leftmost ``rcu_node`` structure offlines its last CPU and if the next ``rcu_node`` structure has no online CPUs). -.. kernel-figure:: TreeRCU-gp-init-1.svg +.. kernel-figure:: TreeRCU-gp-init-2.svg The final ``rcu_gp_init()`` pass through the ``rcu_node`` tree traverses breadth-first, setting each ``rcu_node`` structure's ``->gp_seq`` field to the newly advanced value from the ``rcu_state`` structure, as shown in the following diagram. -.. kernel-figure:: TreeRCU-gp-init-1.svg +.. kernel-figure:: TreeRCU-gp-init-3.svg This change will also cause each CPU's next call to ``__note_gp_changes()`` to notice that a new grace period has started, -- cgit v1.2.3-58-ga151 From d0bfa8b3c411e25e014e4131d2804afe29c440a6 Mon Sep 17 00:00:00 2001 From: Zhang Qiang Date: Thu, 15 Apr 2021 19:19:56 +0200 Subject: kvfree_rcu: Release a page cache under memory pressure Add a drain_page_cache() function to drain a per-cpu page cache. The reason behind of it is a system can run into a low memory condition, in that case a page shrinker can ask for its users to free their caches in order to get extra memory available for other needs in a system. When a system hits such condition, a page cache is drained for all CPUs in a system. By default a page cache work is delayed with 5 seconds interval until a memory pressure disappears, if needed it can be changed. See a rcu_delay_page_cache_fill_msec module parameter. Co-developed-by: Uladzislau Rezki (Sony) Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-parameters.txt | 5 ++ kernel/rcu/tree.c | 82 ++++++++++++++++++++++--- 2 files changed, 78 insertions(+), 9 deletions(-) (limited to 'Documentation') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index cb89dbdedc46..4405fd32e8ab 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4290,6 +4290,11 @@ whole algorithm to behave better in low memory condition. + rcutree.rcu_delay_page_cache_fill_msec= [KNL] + Set the page-cache refill delay (in milliseconds) + in response to low-memory conditions. The range + of permitted values is in the range 0:100000. + 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 8e78b2430c16..74d840aa877b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -186,6 +186,17 @@ module_param(rcu_unlock_delay, int, 0444); static int rcu_min_cached_objs = 5; module_param(rcu_min_cached_objs, int, 0444); +// A page shrinker can ask for pages to be freed to make them +// available for other parts of the system. This usually happens +// under low memory conditions, and in that case we should also +// defer page-cache filling for a short time period. +// +// The default value is 5 seconds, which is long enough to reduce +// interference with the shrinker while it asks other systems to +// drain their caches. +static int rcu_delay_page_cache_fill_msec = 5000; +module_param(rcu_delay_page_cache_fill_msec, int, 0444); + /* Retrieve RCU kthreads priority for rcutorture */ int rcu_get_gp_kthreads_prio(void) { @@ -3171,6 +3182,7 @@ struct kfree_rcu_cpu_work { * Even though it is lockless an access has to be protected by the * per-cpu lock. * @page_cache_work: A work to refill the cache when it is empty + * @backoff_page_cache_fill: Delay cache refills * @work_in_progress: Indicates that page_cache_work is running * @hrtimer: A hrtimer for scheduling a page_cache_work * @nr_bkv_objs: number of allocated objects at @bkvcache. @@ -3190,7 +3202,8 @@ struct kfree_rcu_cpu { bool initialized; int count; - struct work_struct page_cache_work; + struct delayed_work page_cache_work; + atomic_t backoff_page_cache_fill; atomic_t work_in_progress; struct hrtimer hrtimer; @@ -3256,6 +3269,26 @@ put_cached_bnode(struct kfree_rcu_cpu *krcp, } +static int +drain_page_cache(struct kfree_rcu_cpu *krcp) +{ + unsigned long flags; + struct llist_node *page_list, *pos, *n; + int freed = 0; + + raw_spin_lock_irqsave(&krcp->lock, flags); + page_list = llist_del_all(&krcp->bkvcache); + krcp->nr_bkv_objs = 0; + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + llist_for_each_safe(pos, n, page_list) { + free_page((unsigned long)pos); + freed++; + } + + return freed; +} + /* * This function is invoked in workqueue context after a grace period. * It frees all the objects queued on ->bhead_free or ->head_free. @@ -3446,7 +3479,7 @@ schedule_page_work_fn(struct hrtimer *t) struct kfree_rcu_cpu *krcp = container_of(t, struct kfree_rcu_cpu, hrtimer); - queue_work(system_highpri_wq, &krcp->page_cache_work); + queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0); return HRTIMER_NORESTART; } @@ -3455,12 +3488,16 @@ static void fill_page_cache_func(struct work_struct *work) struct kvfree_rcu_bulk_data *bnode; struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, - page_cache_work); + page_cache_work.work); unsigned long flags; + int nr_pages; bool pushed; int i; - for (i = 0; i < rcu_min_cached_objs; i++) { + nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ? + 1 : rcu_min_cached_objs; + + for (i = 0; i < nr_pages; i++) { bnode = (struct kvfree_rcu_bulk_data *) __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); @@ -3477,6 +3514,7 @@ static void fill_page_cache_func(struct work_struct *work) } atomic_set(&krcp->work_in_progress, 0); + atomic_set(&krcp->backoff_page_cache_fill, 0); } static void @@ -3484,10 +3522,15 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) { if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && !atomic_xchg(&krcp->work_in_progress, 1)) { - hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, - HRTIMER_MODE_REL); - krcp->hrtimer.function = schedule_page_work_fn; - hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + if (atomic_read(&krcp->backoff_page_cache_fill)) { + queue_delayed_work(system_wq, + &krcp->page_cache_work, + msecs_to_jiffies(rcu_delay_page_cache_fill_msec)); + } else { + hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + krcp->hrtimer.function = schedule_page_work_fn; + hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + } } } @@ -3639,12 +3682,19 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { int cpu; unsigned long count = 0; + unsigned long flags; /* Snapshot count of all CPUs */ for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); count += READ_ONCE(krcp->count); + + raw_spin_lock_irqsave(&krcp->lock, flags); + count += krcp->nr_bkv_objs; + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + atomic_set(&krcp->backoff_page_cache_fill, 1); } return count; @@ -3661,6 +3711,8 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); count = krcp->count; + count += drain_page_cache(krcp); + raw_spin_lock_irqsave(&krcp->lock, flags); if (krcp->monitor_todo) kfree_rcu_drain_unlock(krcp, flags); @@ -4687,6 +4739,18 @@ static void __init kfree_rcu_batch_init(void) int cpu; int i; + /* Clamp it to [0:100] seconds interval. */ + if (rcu_delay_page_cache_fill_msec < 0 || + rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) { + + rcu_delay_page_cache_fill_msec = + clamp(rcu_delay_page_cache_fill_msec, 0, + (int) (100 * MSEC_PER_SEC)); + + pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n", + rcu_delay_page_cache_fill_msec); + } + for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); @@ -4696,7 +4760,7 @@ static void __init kfree_rcu_batch_init(void) } INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); - INIT_WORK(&krcp->page_cache_work, fill_page_cache_func); + INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func); krcp->initialized = true; } if (register_shrinker(&kfree_rcu_shrinker)) -- cgit v1.2.3-58-ga151