> On Nov 6, 2019, at 4:40 AM, David Sterba <d...@jikos.cz> wrote: > > On Tue, Nov 05, 2019 at 09:19:59AM +0000, Michael Chang wrote: >> The zstd support in btrfs has dependenciy to zstd module and core.img >> grows its size significantly to 75KB on my system. The resulted image >> cannot be installed into btrfs bootloader area in the size of 64KB and >> eventually fails with following message. >> >> /usr/sbin/grub-install: warning: your core.img is unusually large. It >> won't fit in the embedding area. >> /usr/sbin/grub-install: error: filesystem `btrfs' doesn't support >> blocklists. >> >> The patch disabled the zstd support of btrfs in pc-bios platform to >> avoid the regression. The resulting size is 56KB, albeit a bit too close >> to the 64KB but works. This is simple workaround until a proper fix >> landed upstream. > > So combination zstd+btrfs+i386-pc never worked? Removing support for > zstd could lead to unbootable system, but if that has never worked > before it'd be ok to make the build conditional. > > Looking at zstd code, does not seem to be easy to squeeze the asm to > something like 64-56=8K.
Yeah, upstream zstd won’t get down to 8K. We recently did some work to make the decompressor smaller for mobile reducing inlining and excluding variants of some functions. On x86_64 the upstream library went from 84KB -> 63KB uncompressed, and 31KB -> 25KB compressed. If we update GRUB to the latest zstd and define a few macros we can get that gain. But it won’t be 8KB. A custom zstd decompress optimized for size could be made much smaller But that would be a large maintenance burden. For example, we have an “educational decoder” that is 18 KB uncompressed and 8 KB compressed, but it can’t be used in production, since it isn’t hardened against invalid inputs. But, it shows the zstd format can be decompressed with a small library. If we (upstream) add a smaller zstd decompressor, we will put a patch up to use it in GRUB. -Nick _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
