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 21249EB64DA for ; Wed, 28 Jun 2023 09:27:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232676AbjF1J10 (ORCPT ); Wed, 28 Jun 2023 05:27:26 -0400 Received: from out-2.mta0.migadu.com ([91.218.175.2]:43855 "EHLO out-2.mta0.migadu.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233581AbjF1IJf (ORCPT ); Wed, 28 Jun 2023 04:09:35 -0400 Message-ID: <490fd0d8-c0b3-cc26-c658-da35d52b6b56@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1687928159; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qQ68CUVkPH/DtMtvHx22HPkppfpY40d9tzkAnim8HEA=; b=gd14pwcZQ7pAUgNaZvwc6+yhnLoa08VYUHT51t9MTHmJbHRbWHAjqm/MY7AF7bZv896gpi s9Dd4FSxg9q8v1WeWWXfSI/buhDB081atkCewxWYSGCr6AhvGhhFI4nfeKWVbFu5DIavIz xemrMbdSGayHfgkrFfaY+E+fDA+hZUQ= Date: Wed, 28 Jun 2023 12:55:49 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 2/4] blk-flush: count inflight flush_data requests Content-Language: en-US To: Ming Lei Cc: axboe@kernel.dk, tj@kernel.org, hch@lst.de, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com References: <20230627120854.971475-1-chengming.zhou@linux.dev> <20230627120854.971475-3-chengming.zhou@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/6/28 12:13, Ming Lei wrote: > On Tue, Jun 27, 2023 at 08:08:52PM +0800, chengming.zhou@linux.dev wrote: >> From: Chengming Zhou >> >> The flush state machine use a double list to link all inflight >> flush_data requests, to avoid issuing separate post-flushes for >> these flush_data requests which shared PREFLUSH. >> >> So we can't reuse rq->queuelist, this is why we need rq->flush.list >> >> In preparation of the next patch that reuse rq->queuelist for flush >> state machine, we change the double linked list to a u64 counter, >> which count all inflight flush_data requests. >> >> This is ok since we only need to know if there is any inflight >> flush_data request, so a u64 counter is good. The only problem I can >> think of is that u64 counter may overflow, which should be unlikely happen. > > It won't overflow, q->nr_requests is 'unsigned long', which should have > been limited to one more reasonable value, such as 2 * BLK_MQ_MAX_DEPTH, so > u16 should be big enough in theory. Ah, right. q->nr_requests is 'unsigned long' and q->queue_depth is 'unsigned int', so 'unsigned long' counter here won't overflow. Should I change it to smaller 'unsigned short' or just leave it as 'unsigned long' ? (Now the size of struct blk_flush_queue is exactly 64 bytes) Thanks. > >> >> Signed-off-by: Chengming Zhou >> --- >> block/blk-flush.c | 9 +++++---- >> block/blk.h | 5 ++--- >> 2 files changed, 7 insertions(+), 7 deletions(-) >> >> diff --git a/block/blk-flush.c b/block/blk-flush.c >> index dba392cf22be..bb7adfc2a5da 100644 >> --- a/block/blk-flush.c >> +++ b/block/blk-flush.c >> @@ -187,7 +187,8 @@ static void blk_flush_complete_seq(struct request *rq, >> break; >> >> case REQ_FSEQ_DATA: >> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight); >> + list_del_init(&rq->flush.list); >> + fq->flush_data_in_flight++; >> spin_lock(&q->requeue_lock); >> list_add_tail(&rq->queuelist, &q->flush_list); >> spin_unlock(&q->requeue_lock); >> @@ -299,7 +300,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq, >> return; >> >> /* C2 and C3 */ >> - if (!list_empty(&fq->flush_data_in_flight) && >> + if (fq->flush_data_in_flight && >> time_before(jiffies, >> fq->flush_pending_since + FLUSH_PENDING_TIMEOUT)) >> return; >> @@ -374,6 +375,7 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq, >> * the comment in flush_end_io(). >> */ >> spin_lock_irqsave(&fq->mq_flush_lock, flags); >> + fq->flush_data_in_flight--; >> blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error); >> spin_unlock_irqrestore(&fq->mq_flush_lock, flags); >> >> @@ -445,7 +447,7 @@ bool blk_insert_flush(struct request *rq) >> blk_rq_init_flush(rq); >> rq->flush.seq |= REQ_FSEQ_POSTFLUSH; >> spin_lock_irq(&fq->mq_flush_lock); >> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight); >> + fq->flush_data_in_flight++; >> spin_unlock_irq(&fq->mq_flush_lock); >> return false; >> default: >> @@ -496,7 +498,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size, >> >> INIT_LIST_HEAD(&fq->flush_queue[0]); >> INIT_LIST_HEAD(&fq->flush_queue[1]); >> - INIT_LIST_HEAD(&fq->flush_data_in_flight); >> >> return fq; >> >> diff --git a/block/blk.h b/block/blk.h >> index 608c5dcc516b..686712e13835 100644 >> --- a/block/blk.h >> +++ b/block/blk.h >> @@ -15,15 +15,14 @@ struct elevator_type; >> extern struct dentry *blk_debugfs_root; >> >> struct blk_flush_queue { >> + spinlock_t mq_flush_lock; >> unsigned int flush_pending_idx:1; >> unsigned int flush_running_idx:1; >> blk_status_t rq_status; >> unsigned long flush_pending_since; >> struct list_head flush_queue[2]; >> - struct list_head flush_data_in_flight; >> + unsigned long flush_data_in_flight; >> struct request *flush_rq; >> - >> - spinlock_t mq_flush_lock; >> }; > > The part of replacing inflight data rq list with counter looks fine. > > Thanks, > Ming >