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authorTejun Heo <tj@kernel.org>2015-08-18 14:55:34 -0700
committerJens Axboe <axboe@fb.com>2015-08-18 15:49:35 -0700
commit2ee867dcfa2eaef1063b686da55c35878b2da4a2 (patch)
tree7f2babb38e525ce07394042d5dc019e61a46f50c /Documentation/cgroups
parentdd165eb3bb4ef16bcdb75417add40633f38c52b8 (diff)
downloadlinux-2ee867dcfa2eaef1063b686da55c35878b2da4a2.tar.bz2
blkcg: implement interface for the unified hierarchy
blkcg interface grew to be the biggest of all controllers and unfortunately most inconsistent too. The interface files are inconsistent with a number of cloes duplicates. Some files have recursive variants while others don't. There's distinction between normal and leaf weights which isn't intuitive and there are a lot of stat knobs which don't make much sense outside of debugging and expose too much implementation details to userland. In the unified hierarchy, everything is always hierarchical and internal nodes can't have tasks rendering the two structural issues twisting the current interface. The interface has to be updated in a significant anyway and this is a good chance to revamp it as a whole. This patch implements blkcg interface for the unified hierarchy. * (from a previous patch) blkcg is identified by "io" instead of "blkio" on the unified hierarchy. Given that the whole interface is updated anyway, the rename shouldn't carry noticeable conversion overhead. * The original interface consisted of 27 files is replaced with the following three files. blkio.stat : per-blkcg stats blkio.weight : per-cgroup and per-cgroup-queue weight settings blkio.max : per-cgroup-queue bps and iops max limits Documentation/cgroups/unified-hierarchy.txt updated accordingly. v2: blkcg_policy->dfl_cftypes wasn't removed on blkcg_policy_unregister() corrupting the cftypes list. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'Documentation/cgroups')
-rw-r--r--Documentation/cgroups/unified-hierarchy.txt61
1 files changed, 57 insertions, 4 deletions
diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
index 1ee9caf29e57..bd1ce15d5178 100644
--- a/Documentation/cgroups/unified-hierarchy.txt
+++ b/Documentation/cgroups/unified-hierarchy.txt
@@ -27,7 +27,7 @@ CONTENTS
5-3-1. Format
5-3-2. Control Knobs
5-4. Per-Controller Changes
- 5-4-1. blkio
+ 5-4-1. io
5-4-2. cpuset
5-4-3. memory
6. Planned Changes
@@ -203,7 +203,7 @@ other issues. The mapping from nice level to weight isn't obvious or
universal, and there are various other knobs which simply aren't
available for tasks.
-The blkio controller implicitly creates a hidden leaf node for each
+The io controller implicitly creates a hidden leaf node for each
cgroup to host the tasks. The hidden leaf has its own copies of all
the knobs with "leaf_" prefixed. While this allows equivalent control
over internal tasks, it's with serious drawbacks. It always adds an
@@ -438,9 +438,62 @@ may be specified in any order and not all pairs have to be specified.
5-4. Per-Controller Changes
-5-4-1. blkio
+5-4-1. io
-- blk-throttle becomes properly hierarchical.
+- blkio is renamed to io. The interface is overhauled anyway. The
+ new name is more in line with the other two major controllers, cpu
+ and memory, and better suited given that it may be used for cgroup
+ writeback without involving block layer.
+
+- Everything including stat is always hierarchical making separate
+ recursive stat files pointless and, as no internal node can have
+ tasks, leaf weights are meaningless. The operation model is
+ simplified and the interface is overhauled accordingly.
+
+ io.stat
+
+ The stat file. The reported stats are from the point where
+ bio's are issued to request_queue. The stats are counted
+ independent of which policies are enabled. Each line in the
+ file follows the following format. More fields may later be
+ added at the end.
+
+ $MAJ:$MIN rbytes=$RBYTES wbytes=$WBYTES rios=$RIOS wrios=$WIOS
+
+ io.weight
+
+ The weight setting, currently only available and effective if
+ cfq-iosched is in use for the target device. The weight is
+ between 10 and 1000 and defaults to 500. The first line
+ always contains the default weight in the following format to
+ use when per-device setting is missing.
+
+ default $WEIGHT
+
+ Subsequent lines list per-device weights of the following
+ format.
+
+ $MAJ:$MIN $WEIGHT
+
+ Writing "$WEIGHT" or "default $WEIGHT" changes the default
+ setting. Writing "$MAJ:$MIN $WEIGHT" sets per-device weight
+ while "$MAJ:$MIN default" clears it.
+
+ This file is available only on non-root cgroups.
+
+ io.max
+
+ The maximum bandwidth and/or iops setting, only available if
+ blk-throttle is enabled. The file is of the following format.
+
+ $MAJ:$MIN rbps=$RBPS wbps=$WBPS riops=$RIOPS wiops=$WIOPS
+
+ ${R|W}BPS are read/write bytes per second and ${R|W}IOPS are
+ read/write IOs per second. "max" indicates no limit. Writing
+ to the file follows the same format but the individual
+ settings may be ommitted or specified in any order.
+
+ This file is available only on non-root cgroups.
5-4-2. cpuset