On Fri, Aug 18, 2023 at 03:09:35PM +0800, Kemeng Shi wrote: > > Is following comment looks good to you: > > When all reserved primary blocks are consumed, we create meta_bg group and > allocate new primary block at first block or block after backup superblock > (if exsiting) in first group of meta_bg group. > This function is only called when first group of meta_bg is added. Well, it's possible to create a file system where all of the block group descriptors use meta_bg, and there are no "traditional" block group descriptors. And so what happens is if there is no available space in the existing block group descriptors for the new block group, and there are no reserved block group descriptors (I'd remove "primary" as that's not something that we've used traditionally), then what happens is that the meta_bg feature will get enabled, and es->s_first_meta_bg will get set to the first block group that is managed using meta_bg. s_first_meta_bg must be a multiple of EXT4_DESC_PER_BLOCK(sb). Some of this is documented in Documentation/filesystems/ext4/blockgroup.rst already. Cheers, - Ted
