Hi Jens, Tejun, all, about nine months ago, we agreed on a solution for unifying the interface of the proportional-share policy in blkio/io [1]. Angelo and I finally completed it. Let me briefly recall the problem and the solution. The current implementation of cgroups doesn't allow two or more entities, e.g., I/O schedulers, to share the same files. So, if CFQ creates its files for the proportional-share policy, such as, e.g, weight files for blkio/io groups, BFQ cannot attach somehow to them. Thus, to enable people to set group weights with BFQ, I resorted to making BFQ create its own version of these common files, by prepending a bfq prefix. Actually, no legacy code uses these different names, or is likely to do so. Having these two sets of names is simply a source of confusion, as pointed out also, e.g., by Lennart Poettering (CCed here), and acknowledged by Tejun [2]. In [1] we agreed on a solution that solves this problem, by actually making it possible to share cgroups files. Both writing to and reading from a shared file trigger the appropriate operation for each of the entities that share the file. In particular, in case of reading, - if all entities produce the same output, the this common output is shown only once; - if the outputs differ, then every per-entity output is shown, preceded by the name of the entity that produced that output. With this solution, legacy code that, e.g., sets group weights, just works, regardless of the I/O scheduler actually implementing proportional share. But note that this extension is not restricted to only blkio/io. The general group interface now enables files to be shared among multiple entities of any kind. (I have also added a patch to fix some clerical errors in bfq doc, which I found while making the latter consistent with the new interface.) Thanks, Paolo [1] https://lkml.org/lkml/2018/1/4/667 [2] https://github.com/systemd/systemd/issues/7057 Angelo Ruocco (7): kernfs: add function to find kernfs_node without increasing ref counter cgroup: link cftypes of the same subsystem with the same name cgroup: add owner name to cftypes block, bfq: align min and default weights with cfq cgroup: make all functions of all cftypes be invoked block, cfq: allow cgroup files to be shared block, throttle: allow sharing cgroup statistic files Paolo Valente (5): cgroup: add hook seq_show_cft with also the owning cftype as parameter block, cgroup: pass cftype to functions that need to use it block, bfq: use standard file names for the proportional-share policy doc, bfq-iosched: fix a few clerical errors doc, bfq-iosched: make it consistent with the new cgroup interface Documentation/block/bfq-iosched.txt | 31 +++-- block/bfq-cgroup.c | 148 +++++++++++++------- block/bfq-iosched.h | 4 +- block/blk-cgroup.c | 22 +-- block/blk-throttle.c | 24 ++-- block/cfq-iosched.c | 105 +++++++++++---- fs/kernfs/dir.c | 13 ++ include/linux/blk-cgroup.h | 10 +- include/linux/cgroup-defs.h | 14 +- include/linux/cgroup.h | 13 ++ include/linux/kernfs.h | 7 + kernel/cgroup/cgroup.c | 262 +++++++++++++++++++++++++++++------- 12 files changed, 483 insertions(+), 170 deletions(-) -- 2.16.1
