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Date:   Sat, 25 Apr 2020 10:11:25 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Hannes Reinecke <hare@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH V8 08/11] block: add blk_end_flush_machinery
Message-ID: <20200425081125.GA5427@lst.de>
References: <20200424102351.475641-1-ming.lei@redhat.com> <20200424102351.475641-9-ming.lei@redhat.com> <20200424104136.GE28156@lst.de> <20200425034405.GG477579@T590>
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On Sat, Apr 25, 2020 at 11:44:05AM +0800, Ming Lei wrote:
> > FYI, we don't really need the bdev to send a bio anymore, this could just
> > do:
> > 
> > 	bio = bio_alloc(GFP_KERNEL, 0); // XXX: shouldn't this be GFP_NOIO??
> 
> Error handling.

bio_alloc does not fail for allocations that can sleep.

> 
> > 	bio->bi_disk = rq->rq_disk;
> > 	bio->bi_partno = 0;
> > 	bio_associate_blkg(bio); // XXX: actually, shouldn't this come from rq?
> > 	bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
> > 	error = submit_bio_wait(bio);
> > 	bio_put(bio);
> 
> Yeah, that is another way, however I prefer to blkdev_issue_flush
> because it takes less code and we do have the API of blkdev_issue_flush.

It is about the same amount of code, and as commented above I think the
current code uses the wrong blkg assignment.