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Date: Mon, 18 Oct 2021 19:18:43 +0200
From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>
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Cc: Dave Kleikamp <shaggy@kernel.org>, jfs-discussion@lists.sourceforge.net,
	Mike Snitzer <snitzer@redhat.com>, linux-nvme@lists.infradead.org,
	Konstantin Komarov <almaz.alexandrovich@paragon-software.com>,
	Song Liu <song@kernel.org>, dm-devel@redhat.com,
	target-devel@vger.kernel.org, reiserfs-devel@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>, drbd-dev@lists.linbit.com,
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	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
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	Josef Bacik <josef@toxicpanda.com>, Coly Li <colyli@suse.de>,
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	David Sterba <dsterba@suse.com>,
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	linux-block@vger.kernel.org, linux-nfs@vger.kernel.org,
	Theodore Ts'o <tytso@mit.edu>,
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	linux-fsdevel@vger.kernel.org,
	Phillip Lougher <phillip@squashfs.org.uk>, ntfs3@lists.linux.dev,
	linux-btrfs@vger.kernel.org
Subject: Re: [Drbd-dev] don't use ->bd_inode to access the block device size
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On Mon, Oct 18, 2021 at 11:16:08AM -0600, Jens Axboe wrote:
> This looks good to me. Followup question, as it's related - I've got a
> hacky patch that caches the inode size in the bdev:
> 
> https://git.kernel.dk/cgit/linux-block/commit/?h=perf-wip&id=c754951eb7193258c35a574bd1ccccb7c4946ee4
> 
> so we don't have to dip into the inode itself for the fast path. While
> it's obviously not something being proposed for inclusion right now, is
> there a world in which we can make something like that work?

There's just two places that update i_size for block devices:
set_capacity and bdev_set_nr_sectors.  So you just need to update
bd_nr_sectors there and you're done.