From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 05FF31EF36E for ; Sun, 28 Sep 2025 13:30:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759066213; cv=none; b=gRpHcicnK7frFlzrZ1/93NH/86DVhWcfjvsLpYxnKLWfABad2pP2M+a6lDbORFIV/sQLQCJbE1tesKyX/nd37b6bmXq9/jyHX0cSI7cyyPH2T/woBbZbG9onBEHOfadY/1ShsBrZj54aLDu04uB+SS2sl8xOkZ5v5lDJ9qzOLqk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759066213; c=relaxed/simple; bh=QpPECCJJWocogr1hmmxxbjw8juMtrhfzGpQIv4fnoU0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HAOJhmjXiL1od//44o0GE+DtlZstd8F8PJ2568edXYAhAB/PiW2ScfIXptQ0bcmmSEIttpfGBjE/Gh58th0A42RGjK6kYtBY+OeEaKMTsGzDnK3YKwBHq1kds3I9kG+ejqYU7nAFu956XrOJUbNh55kYqXc57dQIb62c+h49qQk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=APrJUZlh; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="APrJUZlh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759066209; 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: in-reply-to:in-reply-to:references:references; bh=NO2W5I0YfcFhRbUTchpDwdQv7olqZScIsLA3MOvRxJk=; b=APrJUZlhSYlt9E/MoshqWVD/yjN7HgZRK+BXgZOhuSVp5dAhWsLORwxSlXTLgRs0elbLk9 WMWwL5HoIJSRnTn20QWjSlUBBvgcHOuDPkdPMeX6EH+PxI3lKyz19DT7JhfnpCFIk+IIDi Y1bSn8uSEqBcgItoCbHIsNRApNvzQQM= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-685-lRnRoxC8MM67EBaNQiil4w-1; Sun, 28 Sep 2025 09:30:05 -0400 X-MC-Unique: lRnRoxC8MM67EBaNQiil4w-1 X-Mimecast-MFC-AGG-ID: lRnRoxC8MM67EBaNQiil4w_1759066203 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3C156195608C; Sun, 28 Sep 2025 13:30:03 +0000 (UTC) Received: from localhost (unknown [10.72.120.3]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 2CA4230001A4; Sun, 28 Sep 2025 13:30:01 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: Mikulas Patocka , Zhaoyang Huang , Dave Chinner , linux-fsdevel@vger.kernel.org, Ming Lei Subject: [PATCH V4 6/6] loop: add hint for handling aio via IOCB_NOWAIT Date: Sun, 28 Sep 2025 21:29:25 +0800 Message-ID: <20250928132927.3672537-7-ming.lei@redhat.com> In-Reply-To: <20250928132927.3672537-1-ming.lei@redhat.com> References: <20250928132927.3672537-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Add hint for using IOCB_NOWAIT to handle loop aio command for avoiding to cause write(especially randwrite) perf regression on sparse backed file. Try IOCB_NOWAIT in the following situations: - backing file is block device OR - READ aio command OR - there isn't any queued blocking async WRITEs, because NOWAIT won't cause contention with blocking WRITE, which often implies exclusive lock With this simple policy, perf regression of randwrite/write on sparse backing file is fixed. Link: https://lore.kernel.org/dm-devel/7d6ae2c9-df8e-50d0-7ad6-b787cb3cfab4@redhat.com/ Signed-off-by: Ming Lei --- drivers/block/loop.c | 61 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 57e33553695b..911262b648ce 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -68,6 +68,7 @@ struct loop_device { struct rb_root worker_tree; struct timer_list timer; bool sysfs_inited; + unsigned lo_nr_blocking_writes; struct request_queue *lo_queue; struct blk_mq_tag_set tag_set; @@ -462,6 +463,33 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, return -EIOCBQUEUED; } +static inline bool lo_aio_try_nowait(struct loop_device *lo, + struct loop_cmd *cmd) +{ + struct file *file = lo->lo_backing_file; + struct inode *inode = file->f_mapping->host; + struct request *rq = blk_mq_rq_from_pdu(cmd); + + /* NOWAIT works fine for backing block device */ + if (S_ISBLK(inode->i_mode)) + return true; + + /* + * NOWAIT is supposed to be fine for READ without contending with + * blocking WRITE + */ + if (req_op(rq) == REQ_OP_READ) + return true; + + /* + * If there is any queued non-NOWAIT async WRITE , don't try new + * NOWAIT WRITE for avoiding contention + * + * Here we focus on handling stable FS block mapping via NOWAIT + */ + return READ_ONCE(lo->lo_nr_blocking_writes) == 0; +} + static int lo_rw_aio_nowait(struct loop_device *lo, struct loop_cmd *cmd, int rw) { @@ -473,6 +501,9 @@ static int lo_rw_aio_nowait(struct loop_device *lo, struct loop_cmd *cmd, if (unlikely(ret)) goto fail; + if (!lo_aio_try_nowait(lo, cmd)) + return -EAGAIN; + cmd->iocb.ki_flags |= IOCB_NOWAIT; ret = lo_submit_rw_aio(lo, cmd, nr_bvec, rw); fail: @@ -773,12 +804,19 @@ static ssize_t loop_attr_dio_show(struct loop_device *lo, char *buf) return sysfs_emit(buf, "%s\n", dio ? "1" : "0"); } +static ssize_t loop_attr_nr_blocking_writes_show(struct loop_device *lo, + char *buf) +{ + return sysfs_emit(buf, "%u\n", lo->lo_nr_blocking_writes); +} + LOOP_ATTR_RO(backing_file); LOOP_ATTR_RO(offset); LOOP_ATTR_RO(sizelimit); LOOP_ATTR_RO(autoclear); LOOP_ATTR_RO(partscan); LOOP_ATTR_RO(dio); +LOOP_ATTR_RO(nr_blocking_writes); static struct attribute *loop_attrs[] = { &loop_attr_backing_file.attr, @@ -787,6 +825,7 @@ static struct attribute *loop_attrs[] = { &loop_attr_autoclear.attr, &loop_attr_partscan.attr, &loop_attr_dio.attr, + &loop_attr_nr_blocking_writes.attr, NULL, }; @@ -862,6 +901,24 @@ static inline int queue_on_root_worker(struct cgroup_subsys_state *css) } #endif +static inline void loop_inc_blocking_writes(struct loop_device *lo, + struct loop_cmd *cmd) +{ + lockdep_assert_held(&lo->lo_mutex); + + if (req_op(blk_mq_rq_from_pdu(cmd)) == REQ_OP_WRITE) + lo->lo_nr_blocking_writes += 1; +} + +static inline void loop_dec_blocking_writes(struct loop_device *lo, + struct loop_cmd *cmd) +{ + lockdep_assert_held(&lo->lo_mutex); + + if (req_op(blk_mq_rq_from_pdu(cmd)) == REQ_OP_WRITE) + lo->lo_nr_blocking_writes -= 1; +} + static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) { struct request __maybe_unused *rq = blk_mq_rq_from_pdu(cmd); @@ -944,6 +1001,8 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) work = &lo->rootcg_work; cmd_list = &lo->rootcg_cmd_list; } + if (cmd->use_aio) + loop_inc_blocking_writes(lo, cmd); list_add_tail(&cmd->list_entry, cmd_list); queue_work(lo->workqueue, work); spin_unlock_irq(&lo->lo_work_lock); @@ -2042,6 +2101,8 @@ static void loop_process_work(struct loop_worker *worker, cond_resched(); spin_lock_irq(&lo->lo_work_lock); + if (cmd->use_aio) + loop_dec_blocking_writes(lo, cmd); } /* -- 2.47.0