From patchwork Wed Feb 1 16:01:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marcelo Tosatti X-Patchwork-Id: 13124653 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 530A9C05027 for ; Wed, 1 Feb 2023 16:04:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232862AbjBAQEo (ORCPT ); Wed, 1 Feb 2023 11:04:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232539AbjBAQEn (ORCPT ); Wed, 1 Feb 2023 11:04:43 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6711E3D92E for ; Wed, 1 Feb 2023 08:03:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675267437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type; bh=AiUOCdYZiZ0EhpszTzQvWhcI8sDqoZDTm+/tkKX62Oo=; b=VP5TzDkf9S18e+CqoEBlbpvYRu1JILNva9zV/GxWD2JgohizIlmqPhMhlt8sBgKQAvQC1T zoyz+prHnfS4QtfMS4tvYtXFSJVW72dKr++hBpW9kphsI+ltjy73s7e280m7Af9bwIK120 oqY/UE0Z16IYCki4gYzibc7SoylFk6w= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-25-hY-NQHINNpGkAjV3mvyciA-1; Wed, 01 Feb 2023 11:03:54 -0500 X-MC-Unique: hY-NQHINNpGkAjV3mvyciA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8E1DE38149AB; Wed, 1 Feb 2023 16:03:53 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9741D404BEC4; Wed, 1 Feb 2023 16:03:52 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 30599403CC75B; Wed, 1 Feb 2023 13:01:47 -0300 (-03) Date: Wed, 1 Feb 2023 13:01:47 -0300 From: Marcelo Tosatti To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: Alexander Viro , Matthew Wilcox , Christoph Hellwig , Jens Axboe , Frederic Weisbecker , Leonardo Bras , Yair Podemsky , P J P Subject: [PATCH v3] fs/buffer.c: update per-CPU bh_lru cache via RCU Message-ID: MIME-Version: 1.0 Content-Disposition: inline X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org umount calls invalidate_bh_lrus which IPIs each CPU that has non empty per-CPU buffer_head cache: on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1); This interrupts CPUs which might be executing code sensitive to interferences. To avoid the IPI, free the per-CPU caches remotely via RCU. Two bh_lrus structures for each CPU are allocated: one is being used (assigned to per-CPU bh_lru pointer), and the other is being freed (or idle). Signed-off-by: Marcelo Tosatti --- v3: fix CPU hotplug v2: fix sparse warnings (kernel test robot) diff --git a/fs/buffer.c b/fs/buffer.c index d9c6d1fbb6dd..0c54ffe9fd62 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1203,7 +1203,21 @@ struct bh_lru { struct buffer_head *bhs[BH_LRU_SIZE]; }; -static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }}; + +/* + * Allocate two bh_lrus structures for each CPU. bh_lru points to the + * one that is currently in use, and the update path does + * (consider cpu->bh_lru = bh_lrus[0]). + * + * cpu->bh_lrup = bh_lrus[1] + * synchronize_rcu() + * free bh's in bh_lrus[0] + */ +static unsigned int bh_lru_idx; +static DEFINE_PER_CPU(struct bh_lru, bh_lrus[2]) = {{{ NULL }}, {{NULL}}}; +static DEFINE_PER_CPU(struct bh_lru __rcu *, bh_lrup); + +static DEFINE_MUTEX(bh_lru_invalidate_mutex); #ifdef CONFIG_SMP #define bh_lru_lock() local_irq_disable() @@ -1245,16 +1259,19 @@ static void bh_lru_install(struct buffer_head *bh) return; } - b = this_cpu_ptr(&bh_lrus); + rcu_read_lock(); + b = rcu_dereference(per_cpu(bh_lrup, smp_processor_id())); for (i = 0; i < BH_LRU_SIZE; i++) { swap(evictee, b->bhs[i]); if (evictee == bh) { + rcu_read_unlock(); bh_lru_unlock(); return; } } get_bh(bh); + rcu_read_unlock(); bh_lru_unlock(); brelse(evictee); } @@ -1266,28 +1283,32 @@ static struct buffer_head * lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size) { struct buffer_head *ret = NULL; + struct bh_lru *lru; unsigned int i; check_irqs_on(); bh_lru_lock(); + rcu_read_lock(); + + lru = rcu_dereference(per_cpu(bh_lrup, smp_processor_id())); for (i = 0; i < BH_LRU_SIZE; i++) { - struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]); + struct buffer_head *bh = lru->bhs[i]; if (bh && bh->b_blocknr == block && bh->b_bdev == bdev && bh->b_size == size) { if (i) { while (i) { - __this_cpu_write(bh_lrus.bhs[i], - __this_cpu_read(bh_lrus.bhs[i - 1])); + lru->bhs[i] = lru->bhs[i - 1]; i--; } - __this_cpu_write(bh_lrus.bhs[0], bh); + lru->bhs[0] = bh; } get_bh(bh); ret = bh; break; } } + rcu_read_unlock(); bh_lru_unlock(); return ret; } @@ -1381,35 +1402,54 @@ static void __invalidate_bh_lrus(struct bh_lru *b) b->bhs[i] = NULL; } } -/* - * invalidate_bh_lrus() is called rarely - but not only at unmount. - * This doesn't race because it runs in each cpu either in irq - * or with preempt disabled. - */ -static void invalidate_bh_lru(void *arg) -{ - struct bh_lru *b = &get_cpu_var(bh_lrus); - - __invalidate_bh_lrus(b); - put_cpu_var(bh_lrus); -} bool has_bh_in_lru(int cpu, void *dummy) { - struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu); + struct bh_lru *b; int i; - + + rcu_read_lock(); + b = rcu_dereference(per_cpu(bh_lrup, cpu)); for (i = 0; i < BH_LRU_SIZE; i++) { - if (b->bhs[i]) + if (b->bhs[i]) { + rcu_read_unlock(); return true; + } } + rcu_read_unlock(); return false; } +/* + * invalidate_bh_lrus() is called rarely - but not only at unmount. + */ void invalidate_bh_lrus(void) { - on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1); + int cpu, oidx; + + mutex_lock(&bh_lru_invalidate_mutex); + cpus_read_lock(); + oidx = bh_lru_idx; + bh_lru_idx++; + if (bh_lru_idx >= 2) + bh_lru_idx = 0; + + /* Assign the per-CPU bh_lru pointer */ + for_each_online_cpu(cpu) + rcu_assign_pointer(per_cpu(bh_lrup, cpu), + per_cpu_ptr(&bh_lrus[bh_lru_idx], cpu)); + synchronize_rcu_expedited(); + + for_each_online_cpu(cpu) { + struct bh_lru *b = per_cpu_ptr(&bh_lrus[oidx], cpu); + + bh_lru_lock(); + __invalidate_bh_lrus(b); + bh_lru_unlock(); + } + cpus_read_unlock(); + mutex_unlock(&bh_lru_invalidate_mutex); } EXPORT_SYMBOL_GPL(invalidate_bh_lrus); @@ -1422,8 +1462,10 @@ void invalidate_bh_lrus_cpu(void) struct bh_lru *b; bh_lru_lock(); - b = this_cpu_ptr(&bh_lrus); + rcu_read_lock(); + b = rcu_dereference(per_cpu(bh_lrup, smp_processor_id())); __invalidate_bh_lrus(b); + rcu_read_unlock(); bh_lru_unlock(); } @@ -2920,15 +2962,25 @@ void free_buffer_head(struct buffer_head *bh) } EXPORT_SYMBOL(free_buffer_head); +static int buffer_cpu_online(unsigned int cpu) +{ + rcu_assign_pointer(per_cpu(bh_lrup, cpu), + per_cpu_ptr(&bh_lrus[bh_lru_idx], cpu)); + return 0; +} + static int buffer_exit_cpu_dead(unsigned int cpu) { int i; - struct bh_lru *b = &per_cpu(bh_lrus, cpu); + struct bh_lru *b; + rcu_read_lock(); + b = rcu_dereference(per_cpu(bh_lrup, cpu)); for (i = 0; i < BH_LRU_SIZE; i++) { brelse(b->bhs[i]); b->bhs[i] = NULL; } + rcu_read_unlock(); this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr); per_cpu(bh_accounting, cpu).nr = 0; return 0; @@ -3021,7 +3073,7 @@ EXPORT_SYMBOL(__bh_read_batch); void __init buffer_init(void) { unsigned long nrpages; - int ret; + int ret, cpu; bh_cachep = kmem_cache_create("buffer_head", sizeof(struct buffer_head), 0, @@ -3029,6 +3081,11 @@ void __init buffer_init(void) SLAB_MEM_SPREAD), NULL); + cpus_read_lock(); + for_each_online_cpu(cpu) + rcu_assign_pointer(per_cpu(bh_lrup, cpu), per_cpu_ptr(&bh_lrus[0], cpu)); + cpus_read_unlock(); + /* * Limit the bh occupancy to 10% of ZONE_NORMAL */ @@ -3037,4 +3094,7 @@ void __init buffer_init(void) ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead", NULL, buffer_exit_cpu_dead); WARN_ON(ret < 0); + ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "fs/buffer:online", + NULL, buffer_cpu_online); + WARN_ON(ret < 0); }