Hi Andrew,
> On Fri, 16 Mar 2018 15:55:53 +0900 shunki-fujita <shunki-fujita@xxxxxxxxxxxx> wrote:
>
> > When changing the size of a block device, its all caches are freed.
> > It's necessary on shrinking to prevent spurious I/Os to the disappeared region.
> > However, on expanding, such kind of I/Os doesn't happen.
> >
> > Similar things can be considered for btrfs filesystem resize and resize2fs,
> > but they are designed not to cache drops when expanding.
> > Therefore this patch removes unnecessary cache drop.
>
> Yes, the patch removes the flush_disk() call when shrinking. But it
> adds additional code which is unchangelogged and uncommented. What's
> happening here?
>
> > --- a/fs/block_dev.c
> > +++ b/fs/block_dev.c
> > @@ -1337,7 +1337,14 @@ void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
> > "%s: detected capacity change from %lld to %lld\n",
> > disk->disk_name, bdev_size, disk_size);
> > i_size_write(bdev->bd_inode, disk_size);
> > - flush_disk(bdev, false);
> > + if (bdev_size > disk_size) {
> > + flush_disk(bdev, false);
> > + } else {
> > + if (!bdev->bd_disk)
> > + return;
> > + if (disk_part_scan_enabled(bdev->bd_disk))
> > + bdev->bd_invalidated = 1;
> > + }
> > }
> > }
>
> Oh, I see. It's a copy-n-paste of some mystery uncommented,
> lost-in-the-mists-of-time code from flush_disk(). Argh.
>
> The world would be a better place if we could move that bit of code
> into a separate function, figure out what it does, document it and call
> it from both sites.
>
This was an unnecessary additional code.
Since bdev-> bd_invalidated always 0 after check_disk_size_change (), no additional code was required.
https://github.com/torvalds/linux/blob/master/fs/block_dev.c#L1365-L1366
I will repost the fix patch.
Thanks,
Shunki
