From: Yu Kuai <[email protected]>
This is v2 of the preparatory series for the blkcg_mutex conversion
proposed in the related series [1]. That conversion moves queue-local
blkg topology synchronization from q->queue_lock to q->blkcg_mutex,
which is awkward while bios directly store queue-local blkg references.
Storing a blkg also ties a bio to one request_queue. A remapped bio must
drop that reference and recreate the association for the new queue even
when no blkcg policy needs it. Dying blkgs add another complication:
they disappear from the per-blkcg lookup tree before all pinned bio
references drain.
Patch 1 makes request_queue the authoritative lookup owner. A
queue-owned rhashtable keyed by the blkcg CSS ID keeps dying blkgs
discoverable until their references drain, while q->blkg_list remains
available for ordered walks.
Patch 2 stores and pins the queue-independent blkcg CSS in each bio.
Queue-local blkgs are created lazily by policy users, then pinned until
the bio changes devices or releases its cgroup state. Completion and
accounting paths which do not create a blkg remain lookup-only.
Patch 3 moves async bio punt state from blkg to blkcg, so punting alone
does not instantiate a queue-local blkg.
Changes since v1:
- Rebase onto the latest block-7.3 branch.
- In patch 2, require every blkg rhashtable lookup to run inside an
explicit RCU read-side critical section. Annotate blkg_lookup_any(),
blkg_lookup(), and recursive wrappers with __must_hold_shared(RCU)
so Clang thread-safety analysis verifies the contract.
- In patch 2, exclude BIO_BLKG_REF from the flags saved by
dm_bio_record(), since restoring an ownership bit cannot recreate
the associated blkg reference.
- In patch 3, use scoped spinlock guards for async_bios and annotate
the list with __guarded_by().
- Add Nilay Shroff's Reviewed-by to patch 1.
Changes since RFC v3:
- Drop the RFC prefix.
- Add Christoph Hellwig's Reviewed-by to patch 1.
- Add Tao Cui's Reviewed-by to patch 2.
- In patch 2, relax blkg_lookup_any()/blkg_lookup() to also allow
q->queue_lock as an alternative to the RCU read lock.
Changes since RFC v2:
- Drop the old patch 1 and send it separately as a bugfix for 7.3 and
-stable, as suggested by Christoph Hellwig.
- Rebase onto the latest for-7.3/block branch.
- In the new patch 1, note that the remaining q->blkg_list walkers are
cgroupfs/sysfs slow paths and can move to rhashtable iteration after
the queue_lock-to-blkcg_mutex conversion.
- In the new patch 1, explain the list_empty case in blkg_release(), and
add an RCU lockdep assertion plus documentation that blkg_lookup_any()
does not acquire a reference.
Changes since RFC v1:
- Add patch 1 to wait for every old blkg to leave q->blkg_list before a
shared request_queue is rebound, instead of treating root_blkg == NULL
as completion of asynchronous blkg teardown.
- Add patch 2 to replace the per-blkcg radix tree and lookup hint with a
request_queue rhashtable keyed by blkcg->css.id, as suggested by
Christoph Hellwig. Keep dying pinned blkgs in the hash until
blkg_release() so bio-owned references remain discoverable.
- Fold the v1 helper-only patch into patch 3, as suggested by Jan Kara and
Christoph Hellwig, and make bio_blkcg() naturally return NULL for an
unassociated bio.
- Rework patch 3 so blkg_lookup_create() acquires the bio-owned reference,
falls back to a live parent when creation or tryget fails, and updates
bi_blkcg when the returned blkg belongs to an ancestor.
- Make bio_blkg_lookup() lookup-only: it returns NULL unless BIO_BLKG_REF
is already set. Use bio_blkg() in the BFQ and IOCOST merge paths which
may need to create a blkg, while keeping blk_cgroup_bio_start() and
completion paths lookup-only.
- Move CSS online-reference handling into
bio_associate_blkcg_from_css(), including fallback to the root blkcg, so
bio_associate_blkcg() does not take a redundant reference.
- Keep the v1 async bio punt conversion as patch 4 and document that
async_bio_lock protects async_bios.
Previous versions:
v1: https://lore.kernel.org/r/[email protected]
RFC v3: https://lore.kernel.org/r/[email protected]
RFC v2: https://lore.kernel.org/r/[email protected]
RFC v1: https://lore.kernel.org/r/[email protected]
Related series:
[1] RFC v2 blk-cgroup: protect blkgs with blkcg_mutex
https://lore.kernel.org/r/[email protected]
Yu Kuai (3):
blk-cgroup: use a request_queue rhashtable for blkg lookup
blk-cgroup: store blkcg in bio instead of blkg
blk-cgroup: move async bio punt state to blkcg
Documentation/admin-guide/cgroup-v2.rst | 2 +-
block/bfq-cgroup.c | 18 +-
block/bfq-iosched.c | 19 +-
block/bio.c | 22 +-
block/blk-cgroup-fc-appid.c | 10 +-
block/blk-cgroup-rwstat.h | 2 +-
block/blk-cgroup.c | 358 ++++++++++++++----------
block/blk-cgroup.h | 93 ++++--
block/blk-core.c | 9 +-
block/blk-crypto-fallback.c | 2 +-
block/blk-iocost.c | 12 +-
block/blk-iolatency.c | 11 +-
block/blk-ioprio.c | 2 +-
block/blk-throttle.c | 3 +-
block/blk-throttle.h | 2 +-
drivers/md/bcache/request.c | 2 +-
drivers/md/dm-bio-record.h | 3 +-
drivers/md/dm.c | 2 +-
drivers/md/md.c | 2 +-
fs/gfs2/lops.c | 3 +-
include/linux/bio.h | 26 +-
include/linux/blk_types.h | 9 +-
include/linux/blkdev.h | 2 +
include/linux/writeback.h | 2 +-
mm/page_io.c | 12 +-
25 files changed, 391 insertions(+), 237 deletions(-)
base-commit: fc34aff88b3bd22146745c75cff0abb3c067cf42
--
2.51.0
