> On Jun 10, 2021, at 12:20 PM, David Sterba <dste...@suse.cz> wrote: > > On Thu, Jun 10, 2021 at 04:50:09PM +0200, Christophe Leroy wrote: >> >> >> Le 10/06/2021 à 15:54, Chris Mason a écrit : >>> >>>> On Jun 10, 2021, at 1:23 AM, Christophe Leroy >>>> <christophe.le...@csgroup.eu> 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. >>> >> >> But if 256K is problematic in other ways, is it worth bumping >> BTRFS_MAX_COMPRESSED to 256K ? >> >> David, in below mail, said that 256K support would require deaper changes. >> So disabling BTRFS >> support seems the easiest solution for the time being, at least for Stable >> (I forgot the Fixes: tag >> and the CC: to stable). >> >> On powerpc, 256k pages is a corner case, it requires customised binutils, so >> I don't think disabling >> BTRFS is a issue there. For hexagon I don't know. > > That it blew up due to the max compressed size is a coincidence. We > could have explicit BUILD_BUG_ONs for page size or other constraints > derived from the page size like INLINE_EXTENT_BUFFER_PAGES. >
Right, the constraint is bigger and more complex than BTRFS_MAX_COMPRESSED. > And there's no such thing like "just bump BTRFS_MAX_COMPRESSED to 256K". > The constant is part of on-disk format for lzo and otherwise changing it > would impact performance so this would need proper evaluation. Sorry, how is it baked into LZO? It definitely will have performance implications, I agree there. -chris
