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Date: Thu, 28 Apr 2016 11:29:08 +0800 From: xiakaixu <xiakaixu@...wei.com> To: Jens Axboe <axboe@...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 δΊ 2016/4/27 23:21, Jens Axboe ει: > 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. > Hi Jens, The modified patch in another mail looks better. Maybe there are still some places coube be improved. You can find them in that mail. -- Regards Kaixu Xia
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