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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD237C433EF for ; Tue, 14 Dec 2021 14:44:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3E2EC6B0075; Tue, 14 Dec 2021 09:44:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 36CD16B0078; Tue, 14 Dec 2021 09:44:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 232A26B007B; Tue, 14 Dec 2021 09:44:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0135.hostedemail.com [216.40.44.135]) by kanga.kvack.org (Postfix) with ESMTP id 149006B0075 for ; Tue, 14 Dec 2021 09:44:45 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id CC450884B7 for ; Tue, 14 Dec 2021 14:44:34 +0000 (UTC) X-FDA: 78916670868.28.537F47F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf08.hostedemail.com (Postfix) with ESMTP id 85FE816000F for ; Tue, 14 Dec 2021 14:44:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639493073; 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=k0FLJWy51PC4iscIi4b8gQDcKZWR9NseSrkpHPzozGI=; b=Vy7Ii1zFH8zdnrmIEkCdA8MZHAjPky9zaKI6znvwdmvG+XRjSs7puvCp8XDPe78szEX3hb HojW0OdnJOyEU5XsLfXNLkO/FsYGVO4TSzS+vb215HPhegtpQU+Dw5THwhUrcVl8lDr92B bMydjl2+KxzO8nSAvw9UGFdtiMnWumM= 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-549-GfPvWsqxNsutgrD8UQHE3A-1; Tue, 14 Dec 2021 09:44:29 -0500 X-MC-Unique: GfPvWsqxNsutgrD8UQHE3A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 21BE21023F51; Tue, 14 Dec 2021 14:44:28 +0000 (UTC) Received: from llong.com (unknown [10.22.17.0]) by smtp.corp.redhat.com (Postfix) with ESMTP id C94EA78C2C; Tue, 14 Dec 2021 14:44:16 +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 v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Date: Tue, 14 Dec 2021 09:44:12 -0500 Message-Id: <20211214144412.447035-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 85FE816000F X-Stat-Signature: qhqeqd6mm5purte9pnpe9qch1jdakuoq Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Vy7Ii1zF; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf08.hostedemail.com: domain of longman@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=longman@redhat.com X-HE-Tag: 1639493070-35569 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 to cover the whole structure including the embedded obj_stock structures. 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 and preempt_{enable/disabl= e}() will not be called for PREEMPT_RT. 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. Using separate local locks will complicate the interaction between obj_stock and the embedding memcg_stock_pcp structures. Signed-off-by: Waiman Long --- mm/memcontrol.c | 51 +++++++++++++++++++++++++++++++------------------ 1 file changed, 32 insertions(+), 19 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a09a7d2e0b1b..2c690eceda54 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2096,7 +2096,12 @@ struct obj_stock { #endif }; =20 +/* + * The local_lock protects the whole memcg_stock_pcp structure including + * the embedded obj_stock structures. + */ 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 +2150,7 @@ static bool consume_stock(struct mem_cgroup *memcg,= unsigned int nr_pages) if (nr_pages > MEMCG_CHARGE_BATCH) return ret; =20 - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); =20 stock =3D this_cpu_ptr(&memcg_stock); if (memcg =3D=3D stock->cached && stock->nr_pages >=3D nr_pages) { @@ -2153,7 +2158,7 @@ static bool consume_stock(struct mem_cgroup *memcg,= unsigned int nr_pages) ret =3D true; } =20 - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); =20 return ret; } @@ -2189,7 +2194,7 @@ static void drain_local_stock(struct work_struct *d= ummy) * 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); =20 stock =3D this_cpu_ptr(&memcg_stock); drain_obj_stock(&stock->irq_obj); @@ -2198,7 +2203,7 @@ static void drain_local_stock(struct work_struct *d= ummy) drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); =20 - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } =20 /* @@ -2210,7 +2215,7 @@ static void refill_stock(struct mem_cgroup *memcg, = unsigned int nr_pages) struct memcg_stock_pcp *stock; unsigned long flags; =20 - local_irq_save(flags); + local_lock_irqsave(&memcg_stock.lock, flags); =20 stock =3D this_cpu_ptr(&memcg_stock); if (stock->cached !=3D memcg) { /* reset if necessary */ @@ -2223,7 +2228,7 @@ static void refill_stock(struct mem_cgroup *memcg, = unsigned int nr_pages) if (stock->nr_pages > MEMCG_CHARGE_BATCH) drain_stock(stock); =20 - local_irq_restore(flags); + local_unlock_irqrestore(&memcg_stock.lock, flags); } =20 /* @@ -2779,29 +2784,34 @@ static struct mem_cgroup *get_mem_cgroup_from_obj= cg(struct obj_cgroup *objcg) * which is cheap in non-preempt kernel. The interrupt context object st= ock * 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 and changes will be made= to + * irq_obj only. + * + * For non-PREEMPT_RT, we are not replacing preempt_disable() by local_l= ock() + * as nesting of task_obj and irq_obj are allowed which may cause lockde= p + * splat if local_lock() is used. Using separate local locks will compli= cate + * the interaction between obj_stock and the broader memcg_stock object. */ 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 =3D 0UL; preempt_disable(); - stock =3D this_cpu_ptr(&memcg_stock); - return &stock->task_obj; + return this_cpu_ptr(&memcg_stock.task_obj); } =20 - local_irq_save(*pflags); - stock =3D this_cpu_ptr(&memcg_stock); - return &stock->irq_obj; + local_lock_irqsave(&memcg_stock.lock, *pflags); + return this_cpu_ptr(&memcg_stock.irq_obj); } =20 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); } =20 /* @@ -7088,9 +7098,12 @@ static int __init mem_cgroup_init(void) cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL, memcg_hotplug_cpu_dead); =20 - 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 =3D per_cpu_ptr(&memcg_stock, cpu); + + INIT_WORK(&stock->work, drain_local_stock); + local_lock_init(&stock->lock); + } =20 for_each_node(node) { struct mem_cgroup_tree_per_node *rtpn; --=20 2.27.0