From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7B6DC433EF for ; Fri, 10 Dec 2021 02:52:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236195AbhLJC4a (ORCPT ); Thu, 9 Dec 2021 21:56:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:46236 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233693AbhLJC42 (ORCPT ); Thu, 9 Dec 2021 21:56:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639104772; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=OvObI7nEXeJiZonfZvXDNg0asabJh1D86F98Up+TTk8=; b=gdfLq9AZsYIyyKj7u7fDsylnlX+xz8IKakibCWCT+E0ow0LYAsIzQ43NBNz3ZKk4Eb77yE 1EIghGOJ9aG7T7EAAMXTjXdtQkHkwjxqKIY4332Aitmx1jeoZSGEDb1gSVXhgh0lLwnOSe Yviz4voDl+qqN8HcDEFsW0DvcUTTl1k= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-349-orEd3y_JP3aOQL36R6lfDw-1; Thu, 09 Dec 2021 21:52:47 -0500 X-MC-Unique: orEd3y_JP3aOQL36R6lfDw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ED35E190B2CA; Fri, 10 Dec 2021 02:52:45 +0000 (UTC) Received: from llong.com (unknown [10.22.32.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3C00F100AE22; Fri, 10 Dec 2021 02:52:39 +0000 (UTC) From: Waiman Long To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Sebastian Andrzej Siewior , Thomas Gleixner , Waiman Long Subject: [PATCH-next v2] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Date: Thu, 9 Dec 2021 21:52:28 -0500 Message-Id: <20211210025228.158196-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Direct calls to local_irq_{save/restore}() and preempt_{enable/disable}() are not appropriate for PREEMPT_RT. To provide better PREEMPT_RT support, change local_irq_{save/restore}() to local_lock_irq{save/restore}() and add a local_lock_t to struct memcg_stock_pcp. Also disable the task and interrupt context optimization for obj_stock as there will be no performance gain in the case of PREEMPT_RT. In this case, task obj_stock will be there but remain unused. Note that preempt_enable() and preempt_disable() in get_obj_stock() and put_obj_stock() are not replaced by local_lock() and local_unlock() as it is possible that a task accessing task_obj may get interrupted and then access irq_obj concurrently. So using local_lock for task_obj access may cause lockdep splat. Signed-off-by: Waiman Long --- mm/memcontrol.c | 41 ++++++++++++++++++++++------------------- 1 file changed, 22 insertions(+), 19 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a09a7d2e0b1b..8bed8e2993e4 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2097,6 +2097,7 @@ struct obj_stock { }; struct memcg_stock_pcp { + local_lock_t lock; struct mem_cgroup *cached; /* this never be root cgroup */ unsigned int nr_pages; struct obj_stock task_obj; @@ -2145,7 +2146,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) if (nr_pages > MEMCG_CHARGE_BATCH) return ret; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); if (memcg == stock->cached && stock->nr_pages >= nr_pages) { @@ -2153,7 +2154,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) ret = true; } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); return ret; } @@ -2189,7 +2190,7 @@ static void drain_local_stock(struct work_struct *dummy) * drain_stock races is that we always operate on local CPU stock * here with IRQ disabled */ - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); drain_obj_stock(&stock->irq_obj); @@ -2198,7 +2199,7 @@ static void drain_local_stock(struct work_struct *dummy) drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -2210,7 +2211,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) struct memcg_stock_pcp *stock; unsigned long flags; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); if (stock->cached != memcg) { /* reset if necessary */ @@ -2223,7 +2224,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) if (stock->nr_pages > MEMCG_CHARGE_BATCH) drain_stock(stock); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -2779,29 +2780,28 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) * which is cheap in non-preempt kernel. The interrupt context object stock * can only be accessed after disabling interrupt. User context code can * access interrupt object stock, but not vice versa. + * + * This task and interrupt context optimization is disabled for PREEMPT_RT + * as there is no performance gain in this case. */ static inline struct obj_stock *get_obj_stock(unsigned long *pflags) { - struct memcg_stock_pcp *stock; - - if (likely(in_task())) { + if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT)) { *pflags = 0UL; preempt_disable(); - stock = this_cpu_ptr(&memcg_stock); - return &stock->task_obj; + return this_cpu_ptr(&memcg_stock.task_obj); } - local_irq_save(*pflags); - stock = this_cpu_ptr(&memcg_stock); - return &stock->irq_obj; + local_lock_irqsave(&memcg_stock.lock, *pflags); + return this_cpu_ptr(&memcg_stock.irq_obj); } static inline void put_obj_stock(unsigned long flags) { - if (likely(in_task())) + if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable(); else - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -7088,9 +7088,12 @@ static int __init mem_cgroup_init(void) cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL, memcg_hotplug_cpu_dead); - for_each_possible_cpu(cpu) - INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work, - drain_local_stock); + for_each_possible_cpu(cpu) { + struct memcg_stock_pcp *stock = per_cpu_ptr(&memcg_stock, cpu); + + INIT_WORK(&stock->work, drain_local_stock); + local_lock_init(&stock->lock); + } for_each_node(node) { struct mem_cgroup_tree_per_node *rtpn; -- 2.27.0 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: [PATCH-next v2] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Date: Thu, 9 Dec 2021 21:52:28 -0500 Message-ID: <20211210025228.158196-1-longman@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639104773; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=OvObI7nEXeJiZonfZvXDNg0asabJh1D86F98Up+TTk8=; b=XFbEN74WKqKzONMxzHNv8zI7D4VN2+nB/kKMke9VhQCSY4FptAWMqV+5R8MyE/mpuDBSw2 xSq5d4M5sG6uAefJYvMryhwFjbAuCzYbW+r6l0zgQ/DCAnzujFIFcsfbAN2AJWbhG6I/R1 TNU+IgJZp7ECEPcjvVSEd6rM4akh2tg= List-ID: Content-Type: text/plain; charset="us-ascii" To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Sebastian Andrzej Siewior , Thomas Gleixner , Waiman Long Direct calls to local_irq_{save/restore}() and preempt_{enable/disable}() are not appropriate for PREEMPT_RT. To provide better PREEMPT_RT support, change local_irq_{save/restore}() to local_lock_irq{save/restore}() and add a local_lock_t to struct memcg_stock_pcp. Also disable the task and interrupt context optimization for obj_stock as there will be no performance gain in the case of PREEMPT_RT. In this case, task obj_stock will be there but remain unused. Note that preempt_enable() and preempt_disable() in get_obj_stock() and put_obj_stock() are not replaced by local_lock() and local_unlock() as it is possible that a task accessing task_obj may get interrupted and then access irq_obj concurrently. So using local_lock for task_obj access may cause lockdep splat. Signed-off-by: Waiman Long --- mm/memcontrol.c | 41 ++++++++++++++++++++++------------------- 1 file changed, 22 insertions(+), 19 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a09a7d2e0b1b..8bed8e2993e4 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2097,6 +2097,7 @@ struct obj_stock { }; struct memcg_stock_pcp { + local_lock_t lock; struct mem_cgroup *cached; /* this never be root cgroup */ unsigned int nr_pages; struct obj_stock task_obj; @@ -2145,7 +2146,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) if (nr_pages > MEMCG_CHARGE_BATCH) return ret; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); if (memcg == stock->cached && stock->nr_pages >= nr_pages) { @@ -2153,7 +2154,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) ret = true; } - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); return ret; } @@ -2189,7 +2190,7 @@ static void drain_local_stock(struct work_struct *dummy) * drain_stock races is that we always operate on local CPU stock * here with IRQ disabled */ - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); drain_obj_stock(&stock->irq_obj); @@ -2198,7 +2199,7 @@ static void drain_local_stock(struct work_struct *dummy) drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -2210,7 +2211,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) struct memcg_stock_pcp *stock; unsigned long flags; - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); stock = this_cpu_ptr(&memcg_stock); if (stock->cached != memcg) { /* reset if necessary */ @@ -2223,7 +2224,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) if (stock->nr_pages > MEMCG_CHARGE_BATCH) drain_stock(stock); - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -2779,29 +2780,28 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) * which is cheap in non-preempt kernel. The interrupt context object stock * can only be accessed after disabling interrupt. User context code can * access interrupt object stock, but not vice versa. + * + * This task and interrupt context optimization is disabled for PREEMPT_RT + * as there is no performance gain in this case. */ static inline struct obj_stock *get_obj_stock(unsigned long *pflags) { - struct memcg_stock_pcp *stock; - - if (likely(in_task())) { + if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT)) { *pflags = 0UL; preempt_disable(); - stock = this_cpu_ptr(&memcg_stock); - return &stock->task_obj; + return this_cpu_ptr(&memcg_stock.task_obj); } - local_irq_save(*pflags); - stock = this_cpu_ptr(&memcg_stock); - return &stock->irq_obj; + local_lock_irqsave(&memcg_stock.lock, *pflags); + return this_cpu_ptr(&memcg_stock.irq_obj); } static inline void put_obj_stock(unsigned long flags) { - if (likely(in_task())) + if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable(); else - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } /* @@ -7088,9 +7088,12 @@ static int __init mem_cgroup_init(void) cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL, memcg_hotplug_cpu_dead); - for_each_possible_cpu(cpu) - INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work, - drain_local_stock); + for_each_possible_cpu(cpu) { + struct memcg_stock_pcp *stock = per_cpu_ptr(&memcg_stock, cpu); + + INIT_WORK(&stock->work, drain_local_stock); + local_lock_init(&stock->lock); + } for_each_node(node) { struct mem_cgroup_tree_per_node *rtpn; -- 2.27.0