Current large bucket layout is a preparation for the future zoned cache
device, by which the cache device bucket can be aligned to zone size and
boundary of the zoned SSD.
Original patch introduces bucket_size_hi in struct cache_sb_disk, this
is problematic and can be improved,
- The bucket size is always power-of-2 value, it is unnecessary to add
extra space in struct cache_sb_disk to store the real size value. Just
using existing bucket_size to store the order of power-of-2 value is
enough.
- The added bucket_size_hi is behind d[SB_JOURNAL_BUCKETS] in struct
cache_sb_disk, which breaks a very implicit restriction from macro
csum_set(). This restriction requires member d[] must be the last
member in data structure to calculate the checksum.
This series is to improve the above issue from user space tools. Basic
ideas of this series are,
- Add BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE incompat feature bit.
When it is set, for bucket size >16MB, bucket_size stores the order
of power-of-2 bucket size value. Then no extra space introduced and
csum_set() has all data to calculate super block checksum.
- Rename struct cache_sb_disk's bucket_size_hi to obso_bucket_size_hi,
and rename the incompat feature bit BCH_FEATURE_INCOMPAT_LARGE_BUCKET
to BCH_FEATURE_INCOMPAT_OBSO_LARGE_BUCKET, to indicate they are not
used anymore and obsoleted.
- If a cache device was created for bucket size >16MB with obsoleted
layout, "bcache show" command still display the expected bucket size
value for legacy compatibility purpose.
Although there almost no one else uses bucket size >16MB except me (the
btree node usage code is not optimized yet), it is still necessary to
fix and improve the layout usage as soon as possible.
Coly Li
---
Coly Li (6):
bcache.h: fix typo from SUUP to SUPP
bcache-tools: only call set_bucket_size() for cache device
bcache.h: add BCH_FEATURE_INCOMPAT_LARGE_BUCKET to
BCH_FEATURE_INCOMPAT_SUPP
bcache-tools: check incompatible feature set
bcache-tools: introduce BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE for
large bucket
bcache-tools: display obsoleted bucket size configuration
bcache.h | 17 +++++++++++------
features.c | 4 +++-
lib.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++----
lib.h | 2 +-
make.c | 3 ++-
5 files changed, 65 insertions(+), 13 deletions(-)
--
2.26.2
