On Jun 10, 2021, at 1:23 AM, Christophe Leroy [off-list ref] wrote:

With a config having PAGE_SIZE set to 256K, BTRFS build fails
with the following message

include/linux/compiler_types.h:326:38: error: call to '__compiletime_assert_791' declared with attribute error: BUILD_BUG_ON failed: (BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0

BTRFS_MAX_COMPRESSED being 128K, BTRFS cannot support platforms with
256K pages at the time being.

There are two platforms that can select 256K pages:
- hexagon
- powerpc

Disable BTRFS when 256K page size is selected.

We’ll have other subpage blocksize concerns with 256K pages, but this BTRFS_MAX_COMPRESSED #define is arbitrary.  It’s just trying to have an upper bound on the amount of memory we’ll need to uncompress a single page’s worth of random reads.

We could change it to max(PAGE_SIZE, 128K) or just bump to 256K.

-chris