linux-kernel - Re: [PATCH] drbd: do not set REQ_PREFLUSH when submitting barrier

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Date:   Wed, 3 May 2023 13:05:57 +0200
From:   Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, drbd-dev@...ts.linbit.com,
        linux-kernel@...r.kernel.org,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        linux-block@...r.kernel.org, Thomas Voegtle <tv@...96.de>
Subject: Re: [PATCH] drbd: do not set REQ_PREFLUSH when submitting barrier

Am 03.05.23 um 06:18 schrieb Christoph Hellwig:
> On Tue, May 02, 2023 at 11:29:22AM +0200, Christoph Böhmwalder wrote:
>>  	struct bio *bio = bio_alloc(device->ldev->backing_bdev, 0,
>> -				    REQ_OP_FLUSH | REQ_PREFLUSH, GFP_NOIO);
>> +				    REQ_OP_FLUSH, GFP_NOIO);
> 
> This isn't going to work.  flush bios are (somewhat confusingly)

Indeed...

> implemented as writes with no data and the preflush flag.  So this
> should be:
> 
> 	REQ_OP_WRITE | REQ_PREFLUSH.
> 
> and it looks like whatever flushing this does hasn't wroked for a long
> time.

Thanks for the hint. I'll prepare a v2 today.

-- 
Christoph Böhmwalder
LINBIT | Keeping the Digital World Running
DRBD HA —  Disaster Recovery — Software defined Storage