From patchwork Sat Mar 22 01:26:10 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ming Lei X-Patchwork-Id: 14026127 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 A13C1259C for ; Sat, 22 Mar 2025 01:26:42 +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=1742606804; cv=none; b=jUSHsfxJWSrrCpJ0/q6oiYhUxIKuA1v4NbvghtF8m20D1+ztB/j7tFU1bvY5Dn1qn3GD83SSNjJ9qH6FFbsEVCbMF+uZX94LDaHSe5RxkFnURq/vfX7vfc7BkeRvMsYhFye69U6K5gvGY6+EC6osuCRwzQ82O6AFCbTim+mWHy0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742606804; c=relaxed/simple; bh=NcAuwn+i8L5oEuXthUIDxYma2alnjm5NSxoSC+LOAzg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FbtKutZIBnLMTOrd7v4VPNdgT6NPKc6jsoz3leL1TN/nifTtkIJAeMBd4H75/wJRp6vwRKwFB080hkrQ/xup+NNEOIPi8p053OG8mxJieQs/KUQoGObnReFAL+mXzdVMr48gDnV2Re/ETUoPCzksZTYZtVXKA0CfHTwJJFquRGs= 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=RMGMak0L; 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="RMGMak0L" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742606801; 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=nUlqBDHfwWUJZK2tW62gTBJFE4Ef6WuSuhLHJpSvsEw=; b=RMGMak0LZB7/bF+NBIWnzDxBRZvQkgxYL6NiJuum3uqVvWChJYkVoyFd9WxV7dxeuDW7mB O+w1cNx/c7rY7b6BmqcgQKeXtFTwTrBsVAbngQv/HkD+BgQ59EIGOIqdNDDawnSSmIskVy yLOkyaHPP+ixdkzmjLpukb6badTiSl0= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-131-yVCNuLI3NP275SQFsWYb3A-1; Fri, 21 Mar 2025 21:26:38 -0400 X-MC-Unique: yVCNuLI3NP275SQFsWYb3A-1 X-Mimecast-MFC-AGG-ID: yVCNuLI3NP275SQFsWYb3A_1742606797 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 307311801A06; Sat, 22 Mar 2025 01:26:36 +0000 (UTC) Received: from localhost (unknown [10.72.120.2]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 6650219560AF; Sat, 22 Mar 2025 01:26:33 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: Christoph Hellwig , Jooyung Han , Mike Snitzer , zkabelac@redhat.com, dm-devel@lists.linux.dev, Alasdair Kergon , Mikulas Patocka , Ming Lei Subject: [PATCH V3 1/5] loop: simplify do_req_filebacked() Date: Sat, 22 Mar 2025 09:26:10 +0800 Message-ID: <20250322012617.354222-2-ming.lei@redhat.com> In-Reply-To: <20250322012617.354222-1-ming.lei@redhat.com> References: <20250322012617.354222-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 lo_rw_aio() is only called for READ/WRITE operation, which can be figured out from request directly, so remove 'rw' parameter from lo_rw_aio(), meantime rename the local variable as 'dir' which makes the check more readable in lo_rw_aio(). Meantime add lo_rw_simple() so that do_req_filebacked() can be simplified in the following way: ``` if (cmd->use_aio) return lo_rw_aio(lo, cmd, pos); else return lo_rw_simple(lo, rq, pos); ``` Reviewed-by: Christoph Hellwig Signed-off-by: Ming Lei --- drivers/block/loop.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 674527d770dc..339b19671450 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -277,6 +277,13 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq, return 0; } +static int lo_rw_simple(struct loop_device *lo, struct request *rq, loff_t pos) +{ + if (req_op(rq) == REQ_OP_READ) + return lo_read_simple(lo, rq, pos); + return lo_write_simple(lo, rq, pos); +} + static void loop_clear_limits(struct loop_device *lo, int mode) { struct queue_limits lim = queue_limits_start_update(lo->lo_queue); @@ -392,13 +399,13 @@ static void lo_rw_aio_complete(struct kiocb *iocb, long ret) lo_rw_aio_do_completion(cmd); } -static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, - loff_t pos, int rw) +static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, loff_t pos) { struct iov_iter iter; struct req_iterator rq_iter; struct bio_vec *bvec; struct request *rq = blk_mq_rq_from_pdu(cmd); + int dir = (req_op(rq) == REQ_OP_READ) ? ITER_DEST : ITER_SOURCE; struct bio *bio = rq->bio; struct file *file = lo->lo_backing_file; struct bio_vec tmp; @@ -440,7 +447,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, } atomic_set(&cmd->ref, 2); - iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq)); + iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq)); iter.iov_offset = offset; cmd->iocb.ki_pos = pos; @@ -449,7 +456,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, cmd->iocb.ki_flags = IOCB_DIRECT; cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0); - if (rw == ITER_SOURCE) + if (dir == ITER_SOURCE) ret = file->f_op->write_iter(&cmd->iocb, &iter); else ret = file->f_op->read_iter(&cmd->iocb, &iter); @@ -490,15 +497,11 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq) case REQ_OP_DISCARD: return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE); case REQ_OP_WRITE: - if (cmd->use_aio) - return lo_rw_aio(lo, cmd, pos, ITER_SOURCE); - else - return lo_write_simple(lo, rq, pos); 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Sat, 22 Mar 2025 01:26:41 +0000 (UTC) Received: from localhost (unknown [10.72.120.2]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0B9271955BFE; Sat, 22 Mar 2025 01:26:39 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: Christoph Hellwig , Jooyung Han , Mike Snitzer , zkabelac@redhat.com, dm-devel@lists.linux.dev, Alasdair Kergon , Mikulas Patocka , Ming Lei Subject: [PATCH V3 2/5] loop: cleanup lo_rw_aio() Date: Sat, 22 Mar 2025 09:26:11 +0800 Message-ID: <20250322012617.354222-3-ming.lei@redhat.com> In-Reply-To: <20250322012617.354222-1-ming.lei@redhat.com> References: <20250322012617.354222-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Cleanup lo_rw_aio() a bit by refactoring it into three parts: - lo_cmd_nr_bvec(), for calculating how many bvecs in this request - lo_rw_aio_prep(), for preparing loop command, which need to be called once - lo_submit_rw_aio(), for submitting this lo command, which can be called multiple times Prepare for trying to handle loop command by NOWAIT read/write IO first. Reviewed-by: Christoph Hellwig Signed-off-by: Ming Lei --- drivers/block/loop.c | 81 ++++++++++++++++++++++++++++++-------------- 1 file changed, 56 insertions(+), 25 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 339b19671450..419ca675342a 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -386,7 +386,6 @@ static void lo_rw_aio_do_completion(struct loop_cmd *cmd) if (!atomic_dec_and_test(&cmd->ref)) return; kfree(cmd->bvec); - cmd->bvec = NULL; if (likely(!blk_should_fake_timeout(rq->q))) blk_mq_complete_request(rq); } @@ -399,24 +398,29 @@ static void lo_rw_aio_complete(struct kiocb *iocb, long ret) lo_rw_aio_do_completion(cmd); } -static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, loff_t pos) +static inline unsigned lo_cmd_nr_bvec(struct loop_cmd *cmd) { - struct iov_iter iter; struct req_iterator rq_iter; - struct bio_vec *bvec; struct request *rq = blk_mq_rq_from_pdu(cmd); - int dir = (req_op(rq) == REQ_OP_READ) ? ITER_DEST : ITER_SOURCE; - struct bio *bio = rq->bio; - struct file *file = lo->lo_backing_file; struct bio_vec tmp; - unsigned int offset; int nr_bvec = 0; - int ret; rq_for_each_bvec(tmp, rq, rq_iter) nr_bvec++; + return nr_bvec; +} + +static int lo_rw_aio_prep(struct loop_device *lo, struct loop_cmd *cmd, + unsigned nr_bvec) +{ + struct request *rq = blk_mq_rq_from_pdu(cmd); + loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset; + if (rq->bio != rq->biotail) { + struct req_iterator rq_iter; + struct bio_vec *bvec; + struct bio_vec tmp; bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec), GFP_NOIO); @@ -434,35 +438,62 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, loff_t pos) *bvec = tmp; bvec++; } - bvec = cmd->bvec; - offset = 0; } else { + cmd->bvec = NULL; + } + cmd->iocb.ki_pos = pos; + cmd->iocb.ki_filp = lo->lo_backing_file; + cmd->iocb.ki_complete = lo_rw_aio_complete; + cmd->iocb.ki_flags = IOCB_DIRECT; + cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0); + + return 0; +} + +static int lo_submit_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, + int nr_bvec) +{ + struct request *rq = blk_mq_rq_from_pdu(cmd); + int dir = (req_op(rq) == REQ_OP_READ) ? ITER_DEST : ITER_SOURCE; + struct file *file = lo->lo_backing_file; + struct iov_iter iter; + int ret; + + if (cmd->bvec) { + iov_iter_bvec(&iter, dir, cmd->bvec, nr_bvec, blk_rq_bytes(rq)); + iter.iov_offset = 0; + } else { + struct bio *bio = rq->bio; + struct bio_vec *bvec = __bvec_iter_bvec(bio->bi_io_vec, + bio->bi_iter); + /* * Same here, this bio may be started from the middle of the * 'bvec' because of bio splitting, so offset from the bvec * must be passed to iov iterator */ - offset = bio->bi_iter.bi_bvec_done; - bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); + iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq)); + iter.iov_offset = bio->bi_iter.bi_bvec_done; } - atomic_set(&cmd->ref, 2); - - iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq)); - iter.iov_offset = offset; - - cmd->iocb.ki_pos = pos; - cmd->iocb.ki_filp = file; - cmd->iocb.ki_complete = lo_rw_aio_complete; - cmd->iocb.ki_flags = IOCB_DIRECT; - cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0); + atomic_set(&cmd->ref, 2); if (dir == ITER_SOURCE) ret = file->f_op->write_iter(&cmd->iocb, &iter); else ret = file->f_op->read_iter(&cmd->iocb, &iter); - lo_rw_aio_do_completion(cmd); + return ret; +} + + +static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd) +{ + unsigned int nr_bvec = lo_cmd_nr_bvec(cmd); + int ret = lo_rw_aio_prep(lo, cmd, nr_bvec); + + if (ret >= 0) + ret = lo_submit_rw_aio(lo, cmd, nr_bvec); if (ret != -EIOCBQUEUED) lo_rw_aio_complete(&cmd->iocb, ret); return 0; @@ -499,7 +530,7 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq) case REQ_OP_WRITE: case REQ_OP_READ: if (cmd->use_aio) - return lo_rw_aio(lo, cmd, pos); + return lo_rw_aio(lo, cmd); else return lo_rw_simple(lo, rq, pos); default: From patchwork Sat Mar 22 01:26:12 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ming Lei X-Patchwork-Id: 14026134 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 7E27628382 for ; 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Reviewed-by: Christoph Hellwig Signed-off-by: Ming Lei --- drivers/block/loop.c | 32 +++++++++++++++++--------------- 1 file changed, 17 insertions(+), 15 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 419ca675342a..c14da87efb07 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -877,11 +877,28 @@ static inline int queue_on_root_worker(struct cgroup_subsys_state *css) static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) { + struct request __maybe_unused *rq = blk_mq_rq_from_pdu(cmd); struct rb_node **node, *parent = NULL; struct loop_worker *cur_worker, *worker = NULL; struct work_struct *work; struct list_head *cmd_list; + /* always use the first bio's css */ + cmd->blkcg_css = NULL; + cmd->memcg_css = NULL; +#ifdef CONFIG_BLK_CGROUP + if (rq->bio) { + cmd->blkcg_css = bio_blkcg_css(rq->bio); +#ifdef CONFIG_MEMCG + if (cmd->blkcg_css) { + cmd->memcg_css = + cgroup_get_e_css(cmd->blkcg_css->cgroup, + &memory_cgrp_subsys); + } +#endif + } +#endif + spin_lock_irq(&lo->lo_work_lock); if (queue_on_root_worker(cmd->blkcg_css)) @@ -1926,21 +1943,6 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, break; } - /* always use the first bio's css */ - cmd->blkcg_css = NULL; - cmd->memcg_css = NULL; -#ifdef CONFIG_BLK_CGROUP - if (rq->bio) { - cmd->blkcg_css = bio_blkcg_css(rq->bio); -#ifdef CONFIG_MEMCG - if (cmd->blkcg_css) { - cmd->memcg_css = - cgroup_get_e_css(cmd->blkcg_css->cgroup, - &memory_cgrp_subsys); - } -#endif - } -#endif loop_queue_work(lo, cmd); return BLK_STS_OK; From patchwork Sat Mar 22 01:26:13 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ming Lei X-Patchwork-Id: 14026133 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 CF209250EC for ; Sat, 22 Mar 2025 01:26:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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This is usually one big win in case that FS block mapping is stable, Mikulas verified [1] that this way improves IO perf by close to 5X in 12jobs sequential read/write test, in which FS block mapping is just stable. Fallback to workqueue in case of -EAGAIN. This way may bring a little cost from the 1st retry, but when running the following write test over loop/sparse_file, the actual effect on randwrite is obvious: ``` truncate -s 4G 1.img #1.img is created on XFS/virtio-scsi losetup -f 1.img --direct-io=on fio --direct=1 --bs=4k --runtime=40 --time_based --numjobs=1 --ioengine=libaio \ --iodepth=16 --group_reporting=1 --filename=/dev/loop0 -name=job --rw=$RW ``` - RW=randwrite: obvious IOPS drop observed - RW=write: a little drop(%5 - 10%) This perf drop on randwrite over sparse file will be addressed in the following patch. BLK_MQ_F_BLOCKING has to be set for calling into .read_iter() or .write_iter() which might sleep even though it is NOWAIT, and the only effect is that rcu read lock is replaced with srcu read lock. Link: https://lore.kernel.org/linux-block/a8e5c76a-231f-07d1-a394-847de930f638@redhat.com/ [1] Signed-off-by: Ming Lei --- drivers/block/loop.c | 51 ++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 47 insertions(+), 4 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index c14da87efb07..3baabf150488 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -90,6 +90,8 @@ struct loop_cmd { #define LOOP_IDLE_WORKER_TIMEOUT (60 * HZ) #define LOOP_DEFAULT_HW_Q_DEPTH 128 +static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd); + static DEFINE_IDR(loop_index_idr); static DEFINE_MUTEX(loop_ctl_mutex); static DEFINE_MUTEX(loop_validate_mutex); @@ -385,6 +387,15 @@ static void lo_rw_aio_do_completion(struct loop_cmd *cmd) if (!atomic_dec_and_test(&cmd->ref)) return; + + /* -EAGAIN could be returned from bdev's ->ki_complete */ + if (cmd->ret == -EAGAIN) { + struct loop_device *lo = rq->q->queuedata; + + loop_queue_work(lo, cmd); + return; + } + kfree(cmd->bvec); if (likely(!blk_should_fake_timeout(rq->q))) blk_mq_complete_request(rq); @@ -490,15 +501,38 @@ static int lo_submit_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd) { unsigned int nr_bvec = lo_cmd_nr_bvec(cmd); - int ret = lo_rw_aio_prep(lo, cmd, nr_bvec); + int ret; - if (ret >= 0) - ret = lo_submit_rw_aio(lo, cmd, nr_bvec); + /* + * This command is prepared, and we have tried IOCB_NOWAIT, but got + * -EAGAIN, so clear it now + */ + cmd->iocb.ki_flags &= ~IOCB_NOWAIT; + ret = lo_submit_rw_aio(lo, cmd, nr_bvec); if (ret != -EIOCBQUEUED) lo_rw_aio_complete(&cmd->iocb, ret); return 0; } +static blk_status_t lo_rw_aio_nowait(struct loop_device *lo, + struct loop_cmd *cmd) +{ + unsigned int nr_bvec = lo_cmd_nr_bvec(cmd); + int ret = lo_rw_aio_prep(lo, cmd, nr_bvec); + + if (unlikely(ret < 0)) + return BLK_STS_IOERR; + + cmd->iocb.ki_flags |= IOCB_NOWAIT; + ret = lo_submit_rw_aio(lo, cmd, nr_bvec); + if (ret == -EAGAIN) + return BLK_STS_AGAIN; + + if (ret != -EIOCBQUEUED) + lo_rw_aio_complete(&cmd->iocb, ret); + return BLK_STS_OK; +} + static int do_req_filebacked(struct loop_device *lo, struct request *rq) { struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq); @@ -1943,6 +1977,14 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, break; } + if (cmd->use_aio) { + blk_status_t res = lo_rw_aio_nowait(lo, cmd); + + if (res != BLK_STS_AGAIN) + return res; + /* fallback to workqueue for handling aio */ + } + loop_queue_work(lo, cmd); return BLK_STS_OK; @@ -2093,7 +2135,8 @@ static int loop_add(int i) lo->tag_set.queue_depth = hw_queue_depth; lo->tag_set.numa_node = NUMA_NO_NODE; lo->tag_set.cmd_size = sizeof(struct loop_cmd); - lo->tag_set.flags = BLK_MQ_F_STACKING | BLK_MQ_F_NO_SCHED_BY_DEFAULT; + lo->tag_set.flags = BLK_MQ_F_STACKING | BLK_MQ_F_NO_SCHED_BY_DEFAULT | + BLK_MQ_F_BLOCKING; lo->tag_set.driver_data = lo; err = blk_mq_alloc_tag_set(&lo->tag_set); From patchwork Sat Mar 22 01:26:14 2025 Content-Type: text/plain; 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Sat, 22 Mar 2025 01:26:57 +0000 (UTC) Received: from localhost (unknown [10.72.120.2]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 4934D180174E; Sat, 22 Mar 2025 01:26:55 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: Christoph Hellwig , Jooyung Han , Mike Snitzer , zkabelac@redhat.com, dm-devel@lists.linux.dev, Alasdair Kergon , Mikulas Patocka , Ming Lei Subject: [PATCH V3 5/5] loop: add hint for handling aio via IOCB_NOWAIT Date: Sat, 22 Mar 2025 09:26:14 +0800 Message-ID: <20250322012617.354222-6-ming.lei@redhat.com> In-Reply-To: <20250322012617.354222-1-ming.lei@redhat.com> References: <20250322012617.354222-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 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 | 56 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 3baabf150488..e1b01285da2a 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; @@ -514,6 +515,33 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd) return 0; } +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 blk_status_t lo_rw_aio_nowait(struct loop_device *lo, struct loop_cmd *cmd) { @@ -523,6 +551,9 @@ static blk_status_t lo_rw_aio_nowait(struct loop_device *lo, if (unlikely(ret < 0)) return BLK_STS_IOERR; + if (!lo_aio_try_nowait(lo, cmd)) + return BLK_STS_AGAIN; + cmd->iocb.ki_flags |= IOCB_NOWAIT; ret = lo_submit_rw_aio(lo, cmd, nr_bvec); if (ret == -EAGAIN) @@ -820,12 +851,19 @@ 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, @@ -834,6 +872,7 @@ static struct attribute *loop_attrs[] = { &loop_attr_autoclear.attr, &loop_attr_partscan.attr, &loop_attr_dio.attr, + &loop_attr_nr_blocking_writes.attr, NULL, }; @@ -909,6 +948,19 @@ static inline int queue_on_root_worker(struct cgroup_subsys_state *css) } #endif +static inline void loop_update_blocking_writes(struct loop_device *lo, + struct loop_cmd *cmd, bool inc) +{ + lockdep_assert_held(&lo->lo_mutex); + + if (req_op(blk_mq_rq_from_pdu(cmd)) == REQ_OP_WRITE) { + if (inc) + lo->lo_nr_blocking_writes += 1; + else + 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); @@ -991,6 +1043,8 @@ 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_update_blocking_writes(lo, cmd, true); list_add_tail(&cmd->list_entry, cmd_list); queue_work(lo->workqueue, work); spin_unlock_irq(&lo->lo_work_lock); @@ -2057,6 +2111,8 @@ static void loop_process_work(struct loop_worker *worker, cond_resched(); spin_lock_irq(&lo->lo_work_lock); + if (cmd->use_aio) + loop_update_blocking_writes(lo, cmd, false); } /*