On 2021/2/20 上午10:47, Erik Jensen wrote:

On Thu, Feb 18, 2021 at 12:59 AM Qu Wenruo [off-list ref] wrote:

quoted

Just send a mail to the fs-devel mail list, titled "page->index
limitation on 32bit system?".

I guess your experience as a real world user would definitely bring more
weight to the discussion.

Thanks,
Qu

Given that it sounds like the issue is the metadata address space, and
given that I surely don't actually have 16TiB of metadata on a 24TiB
file system (indeed, Metadata, RAID1: total=30.00GiB, used=28.91GiB),
is there any way I could compact the metadata offsets into the lower
16TiB of the virtual metadata inode? Perhaps that could be something
balance could be taught to do? (Obviously, the initial run of such a
balance would have to be performed using a 64-bit system.)

Unfortunately, no.

Btrfs relies on increasing bytenr in the logical address space for
things like balance, thus we can't relocate chunks to smaller bytenr.

Perhaps, on 32-bit, btrfs itself or some monitoring tool could even
kick off such a metadata balance automatically when the offset hits
10TiB to hopefully avoid ever reaching 16TiB?

That would be worse, as each balanced block group can only go higher
bytenr, not lower, thus it will speed up the problem.

Thanks,
Qu