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Message-ID: <5720D90F.6000609@fb.com>
Date: Wed, 27 Apr 2016 09:21:51 -0600
From: Jens Axboe <axboe@...com>
To: xiakaixu <xiakaixu@...wei.com>
CC: <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
<linux-block@...r.kernel.org>, <jack@...e.cz>,
<dchinner@...hat.com>, <sedat.dilek@...il.com>,
"miaoxie (A)" <miaoxie@...wei.com>, Huxinwei <huxinwei@...wei.com>,
Bintian <bintian.wang@...wei.com>
Subject: Re: [PATCH 7/8] wbt: add general throttling mechanism
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
View attachment "wbt-disable-wakeup.patch" of type "text/x-patch" (913 bytes)
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