Can be fetched from github:
https://github.com/adam900710/btrfs-progs/tree/mkfs_rootdir_rework
And fetching from github is preferred method to test, as this patchset
has 2 prerequisite:
1) Minimal device size patchset
The image size estimate algorithm heavily relies on the minimal
device size calculation
2) Rootdir refactor
To make life a little easier.
Both the prerequisite has no further modification in this patchset, just the
version submitted to mail list, and rebased to v4.13.3 without any
conflict.
Rework 'mkfs.btrfs --rootdir' by:
1) Not using custom chunk allocator
Use btrfs_alloc_chunk() only.
Although currently chunk allocator in btrfs-progs is not small device
friendly, which will try to allocate large chunk.
This can be addressed by image size estimate algorithm, so it won't
cause too much problem.
(But still, it follow the minimal device size from normal mkfs, which
is over 100M for default profile)
2) New image size estimate algorithm
Use over-reserve-for-metadata method, which should ensure we can write
all content into the image.
And rely later shrink the shrink the fs size to minimal.
Although the method itself is based on over-reserve, but in fact it's
quite space efficient in most case.
For empty file case, we will use the allocated data/meta space
allocated in normal mkfs, so no shrink really needed.
For large file and small metadata case, the size difference between
shrunk and unshrunk image is less than 1%.
Although due to the nature we over-reserve for metadata, for
extremely unbalanced data/meta case, like tons of empty files, we
really need to rely shrink functionality.
And the algorithm itself only needs minimal amount of data.
It only uses number of inodes and file size of each regular inode.
3) Shrinking the fs by device extent
As implemented in almost all version of rework which includes
shrinking, tried and true, and easier to implement.
And shrinking is completely independent now, can be easily modified
to shrink multi-device btrfs.
4) Separate shrink functionality to '--shrink' option
This causes less confusion.
And due to my poor English, I only added basic explanation to the
mkfs doc. Although I think this is enough since each functionality
is easier to understand.
5) Not wasting IO to wipe the whole image
Only to wipe the first 1M and create sparse file.
Qu Wenruo (7):
btrfs-progs: mkfs: Don't use custom chunk allocator for rootdir
btrfs-progs: mkfs/rootdir: Use over-reserve method to make size
estimate easier
btrfs-progs: mkfs: Only zero out the first 1M for rootdir
btrfs-progs: mkfs/rootdir: Introduce function to get end position of
last device extent
btrfs-progs: mkfs/rootdir: Shrink fs for rootdir option
btrfs-progs: mkfs: Update allocation info before verbose output
btrfs-progs: mkfs: Separate shrink from rootdir
Documentation/mkfs.btrfs.asciidoc | 11 ++
mkfs/main.c | 260 -
mkfs/rootdir.c| 292 +-
mkfs/rootdir.h| 6 +-
4 files changed, 400 insertions(+), 169 deletions(-)
--
2.14.2
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