on 8/19/2023 12:54 AM, Theodore Ts'o wrote: > 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. > As these information into comment of add_new_gdb_meta_bg could help to some dgree. I summary the information to: 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, then 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 and s_first_meta_bg must be a multiple of EXT4_DESC_PER_BLOCK(sb). This function will be called when first group of meta_bg is added to bring new group descriptors block of new added meta_bg. Or I will leave comments unchange in next version if it's redundant to you. Thanks! > Cheers, > > - Ted >
