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From: Jens Axboe <axboe@fb.com>
To: xiakaixu <xiakaixu@huawei.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
	<linux-block@vger.kernel.org>, <jack@suse.cz>,
	<dchinner@redhat.com>, <sedat.dilek@gmail.com>,
	"miaoxie (A)" <miaoxie@huawei.com>,
	Huxinwei <huxinwei@huawei.com>, Bintian <bintian.wang@huawei.com>
Subject: Re: [PATCH 7/8] wbt: add general throttling mechanism
Date: Wed, 27 Apr 2016 09:21:51 -0600
Message-ID: <5720D90F.6000609@fb.com> (raw)
In-Reply-To: <5720AB61.8010109@huawei.com>


[-- Attachment #1: Type: text/plain, Size: 1144 bytes --]

On 04/27/2016 06:06 AM, xiakaixu wrote:
>> +void __wbt_done(struct rq_wb *rwb)
>> +{
>> +	int inflight, limit = rwb->wb_normal;
>> +
>> +	/*
>> +	 * If the device does write back caching, drop further down
>> +	 * before we wake people up.
>> +	 */
>> +	if (rwb->wc && !atomic_read(&rwb->bdi->wb.dirty_sleeping))
>> +		limit = 0;
>> +	else
>> +		limit = rwb->wb_normal;
>> +
>> +	/*
>> +	 * Don't wake anyone up if we are above the normal limit. If
>> +	 * throttling got disabled (limit == 0) with waiters, ensure
>> +	 * that we wake them up.
>> +	 */
>> +	inflight = atomic_dec_return(&rwb->inflight);
>> +	if (limit && inflight >= limit) {
>> +		if (!rwb->wb_max)
>> +			wake_up_all(&rwb->wait);
>> +		return;
>> +	}
>> +
> Hi Jens,
>
> Just a little confused about this. The rwb->wb_max can't be 0 if the variable
> 'limit' does not equal to 0. So the if (!rwb->wb_max) branch maybe does not
> make sense.

You are right, it doesn't make a lot of sense. I think it suffers from 
code shuffling. How about the attached? The important part is that we 
wake up waiters, if wbt got disabled while we had tracked IO in flight.

-- 
Jens Axboe


[-- Attachment #2: wbt-disable-wakeup.patch --]
[-- Type: text/x-patch, Size: 912 bytes --]

diff --git a/lib/wbt.c b/lib/wbt.c
index 650da911f24f..a6b80c135510 100644
--- a/lib/wbt.c
+++ b/lib/wbt.c
@@ -98,18 +98,23 @@ void __wbt_done(struct rq_wb *rwb)
 	else
 		limit = rwb->wb_normal;
 
+	inflight = atomic_dec_return(&rwb->inflight);
+
 	/*
-	 * Don't wake anyone up if we are above the normal limit. If
-	 * throttling got disabled (limit == 0) with waiters, ensure
-	 * that we wake them up.
+	 * wbt got disabled with IO in flight. Wake up any potential
+	 * waiters, we don't have to do more than that.
 	 */
-	inflight = atomic_dec_return(&rwb->inflight);
-	if (limit && inflight >= limit) {
-		if (!rwb->wb_max)
-			wake_up_all(&rwb->wait);
+	if (!rwb_enabled(rwb)) {
+		wake_up_all(&rwb->wait);
 		return;
 	}
 
+	/*
+	 * Don't wake anyone up if we are above the normal limit.
+	 */
+	if (inflight >= limit)
+		return;
+
 	if (waitqueue_active(&rwb->wait)) {
 		int diff = limit - inflight;
 

  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-26 15:55 [PATCHSET v5] Make background writeback great again for the first time Jens Axboe
2016-04-26 15:55 ` [PATCH 1/8] block: add WRITE_BG Jens Axboe
2016-04-26 15:55 ` [PATCH 2/8] writeback: add wbc_to_write_cmd() Jens Axboe
2016-04-26 15:55 ` [PATCH 3/8] writeback: use WRITE_BG for kupdate and background writeback Jens Axboe
2016-04-26 15:55 ` [PATCH 4/8] writeback: track if we're sleeping on progress in balance_dirty_pages() Jens Axboe
2016-04-26 15:55 ` [PATCH 5/8] block: add code to track actual device queue depth Jens Axboe
2016-04-26 15:55 ` [PATCH 6/8] block: add scalable completion tracking of requests Jens Axboe
2016-05-05  7:52   ` Ming Lei
2016-04-26 15:55 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe
2016-04-27 12:06   ` xiakaixu
2016-04-27 15:21     ` Jens Axboe [this message]
2016-04-28  3:29       ` xiakaixu
2016-04-28 11:05   ` Jan Kara
2016-04-28 18:53     ` Jens Axboe
2016-04-28 19:03       ` Jens Axboe
2016-05-03  9:34       ` Jan Kara
2016-05-03 14:23         ` Jens Axboe
2016-05-03 15:22           ` Jan Kara
2016-05-03 15:32             ` Jens Axboe
2016-05-03 15:40         ` Jan Kara
2016-05-03 15:48           ` Jan Kara
2016-05-03 16:59             ` Jens Axboe
2016-05-03 18:14               ` Jens Axboe
2016-05-03 19:07                 ` Jens Axboe
2016-04-26 15:55 ` [PATCH 8/8] writeback: throttle buffered writeback Jens Axboe
2016-04-27 18:01 ` [PATCHSET v5] Make background writeback great again for the first time Jan Kara
2016-04-27 18:17   ` Jens Axboe
2016-04-27 20:37     ` Jens Axboe
2016-04-27 20:59       ` Jens Axboe
2016-04-28  4:06         ` xiakaixu
2016-04-28 18:36           ` Jens Axboe
2016-04-28 11:54         ` Jan Kara
2016-04-28 18:46           ` Jens Axboe
2016-05-03 12:17             ` Jan Kara
2016-05-03 12:40               ` Chris Mason
2016-05-03 13:06                 ` Jan Kara
2016-05-03 13:42                   ` Chris Mason
2016-05-03 13:57                     ` Jan Kara
2016-05-11 16:36               ` Jan Kara
2016-05-13 18:29                 ` Jens Axboe
2016-05-16  7:47                   ` Jan Kara
2016-08-31 17:05 [PATCHSET v6] Throttled background buffered writeback Jens Axboe
2016-08-31 17:05 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe
2016-09-01 18:05   ` Omar Sandoval
2016-09-01 18:51     ` Jens Axboe
2016-09-07 14:46 [PATCH 0/8] Throttled background buffered writeback v7 Jens Axboe
2016-09-07 14:46 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe

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