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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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Subject: Re: don't use ->bd_inode to access the block device size v3
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References: <20211018101130.1838532-1-hch@lst.de> <4a8c3a39-9cd3-5b2f-6d0f-a16e689755e6@kernel.dk>
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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.