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Date:   Fri, 14 Feb 2020 16:08:50 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc:     David Sterba <dsterba@suse.cz>,
        Nikolay Borisov <nborisov@suse.com>,
        Josef Bacik <josef@toxicpanda.com>,
        "linux-btrfs @ vger . kernel . org" <linux-btrfs@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v8 5/8] btrfs: use BIOs instead of buffer_heads from
 superblock writeout
Message-ID: <20200214150850.GY2902@twin.jikos.cz>
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        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
        Nikolay Borisov <nborisov@suse.com>,
        Josef Bacik <josef@toxicpanda.com>,
        "linux-btrfs @ vger . kernel . org" <linux-btrfs@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
References: <20200213152436.13276-1-johannes.thumshirn@wdc.com>
 <20200213152436.13276-6-johannes.thumshirn@wdc.com>
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On Fri, Feb 14, 2020 at 12:24:33AM +0900, Johannes Thumshirn wrote:
> +		/*
> +		 * Directly use BIOs here instead of relying on the page-cache
> +		 * to do I/O, so we don't loose the ability to do integrity
> +		 * checking.
> +		 */
> +		bio = bio_alloc(GFP_NOFS, 1);
> +		bio_set_dev(bio, device->bdev);
> +		bio->bi_iter.bi_sector = bytenr >> SECTOR_SHIFT;
> +		bio->bi_private = device;
> +		bio->bi_end_io = btrfs_end_super_write;

As a potential future cleanup and simplification, the per-device flush
bio can be used here and not a new one allocated. The flush bios are
sent synchronously and are free for later use by the async submit
writes.