From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Subject: Re: don't use ->bd_inode to access the block device size
	v3
Date: Mon, 18 Oct 2021 19:18:43 +0200
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To: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>
Cc: Dave Kleikamp <shaggy-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, jfs-discussion-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Konstantin Komarov <almaz.alexandrovich-m5I1DM4ARimttCpgsWEBFlaTQe2KTcn/@public.gmane.org>, Song Liu <song-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, reiserfs-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>, drbd-dev-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org, linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, OGAWA Hirofumi <hirofumi-UIVanBePwB70ZhReMnHkpc8NsWr+9BEh@public.gmane.org>, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Josef Bacik <josef-DigfWCa+lFGyeJad7bwFQA@public.gmane.org>, Coly Li <colyli-l3A5Bk7waGM@public.gmane.org>, linux-raid-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, David Sterba <dsterba-IBi9RG/b67k@public.gmane.org>, Ryusuke Konishi <konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Anton Altaparmakov <anton-yrGDUoBaLx3QT0dZR+AlfA@public.gmane.org>, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>, linux-ntfs-dev@li

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.