diff options
Diffstat (limited to 'Documentation/cgroups')
| -rw-r--r-- | Documentation/cgroups/cgroups.txt | 3 | ||||
| -rw-r--r-- | Documentation/cgroups/devices.txt | 70 | ||||
| -rw-r--r-- | Documentation/cgroups/memory.txt | 72 |
3 files changed, 139 insertions, 6 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index bcf1a00b06a..638bf17ff86 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -442,7 +442,7 @@ You can attach the current shell task by echoing 0: You can use the cgroup.procs file instead of the tasks file to move all threads in a threadgroup at once. Echoing the PID of any task in a threadgroup to cgroup.procs causes all tasks in that threadgroup to be -be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks +attached to the cgroup. Writing 0 to cgroup.procs moves all tasks in the writing task's threadgroup. Note: Since every task is always a member of exactly one cgroup in each @@ -580,6 +580,7 @@ propagation along the hierarchy. See the comment on cgroup_for_each_descendant_pre() for details. void css_offline(struct cgroup *cgrp); +(cgroup_mutex held by caller) This is the counterpart of css_online() and called iff css_online() has succeeded on @cgrp. This signifies the beginning of the end of diff --git a/Documentation/cgroups/devices.txt b/Documentation/cgroups/devices.txt index 16624a7f822..3c1095ca02e 100644 --- a/Documentation/cgroups/devices.txt +++ b/Documentation/cgroups/devices.txt @@ -13,9 +13,7 @@ either an integer or * for all. Access is a composition of r The root device cgroup starts with rwm to 'all'. A child device cgroup gets a copy of the parent. Administrators can then remove devices from the whitelist or add new entries. A child cgroup can -never receive a device access which is denied by its parent. However -when a device access is removed from a parent it will not also be -removed from the child(ren). +never receive a device access which is denied by its parent. 2. User Interface @@ -50,3 +48,69 @@ task to a new cgroup. (Again we'll probably want to change that). A cgroup may not be granted more permissions than the cgroup's parent has. + +4. Hierarchy + +device cgroups maintain hierarchy by making sure a cgroup never has more +access permissions than its parent. Every time an entry is written to +a cgroup's devices.deny file, all its children will have that entry removed +from their whitelist and all the locally set whitelist entries will be +re-evaluated. In case one of the locally set whitelist entries would provide +more access than the cgroup's parent, it'll be removed from the whitelist. + +Example: + A + / \ + B + + group behavior exceptions + A allow "b 8:* rwm", "c 116:1 rw" + B deny "c 1:3 rwm", "c 116:2 rwm", "b 3:* rwm" + +If a device is denied in group A: + # echo "c 116:* r" > A/devices.deny +it'll propagate down and after revalidating B's entries, the whitelist entry +"c 116:2 rwm" will be removed: + + group whitelist entries denied devices + A all "b 8:* rwm", "c 116:* rw" + B "c 1:3 rwm", "b 3:* rwm" all the rest + +In case parent's exceptions change and local exceptions are not allowed +anymore, they'll be deleted. + +Notice that new whitelist entries will not be propagated: + A + / \ + B + + group whitelist entries denied devices + A "c 1:3 rwm", "c 1:5 r" all the rest + B "c 1:3 rwm", "c 1:5 r" all the rest + +when adding "c *:3 rwm": + # echo "c *:3 rwm" >A/devices.allow + +the result: + group whitelist entries denied devices + A "c *:3 rwm", "c 1:5 r" all the rest + B "c 1:3 rwm", "c 1:5 r" all the rest + +but now it'll be possible to add new entries to B: + # echo "c 2:3 rwm" >B/devices.allow + # echo "c 50:3 r" >B/devices.allow +or even + # echo "c *:3 rwm" >B/devices.allow + +Allowing or denying all by writing 'a' to devices.allow or devices.deny will +not be possible once the device cgroups has children. + +4.1 Hierarchy (internal implementation) + +device cgroups is implemented internally using a behavior (ALLOW, DENY) and a +list of exceptions. The internal state is controlled using the same user +interface to preserve compatibility with the previous whitelist-only +implementation. Removal or addition of exceptions that will reduce the access +to devices will be propagated down the hierarchy. +For every propagated exception, the effective rules will be re-evaluated based +on current parent's access rules. diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 8b8c28b9864..09027a9fece 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -40,6 +40,7 @@ Features: - soft limit - moving (recharging) account at moving a task is selectable. - usage threshold notifier + - memory pressure notifier - oom-killer disable knob and oom-notifier - Root cgroup has no limit controls. @@ -65,6 +66,7 @@ Brief summary of control files. memory.stat # show various statistics memory.use_hierarchy # set/show hierarchical account enabled memory.force_empty # trigger forced move charge to parent + memory.pressure_level # set memory pressure notifications memory.swappiness # set/show swappiness parameter of vmscan (See sysctl's vm.swappiness) memory.move_charge_at_immigrate # set/show controls of moving charges @@ -194,7 +196,7 @@ the cgroup that brought it in -- this will happen on memory pressure). But see section 8.2: when moving a task to another cgroup, its pages may be recharged to the new cgroup, if move_charge_at_immigrate has been chosen. -Exception: If CONFIG_CGROUP_CGROUP_MEMCG_SWAP is not used. +Exception: If CONFIG_MEMCG_SWAP is not used. When you do swapoff and make swapped-out pages of shmem(tmpfs) to be backed into memory in force, charges for pages are accounted against the caller of swapoff rather than the users of shmem. @@ -762,7 +764,73 @@ At reading, current status of OOM is shown. under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may be stopped.) -11. TODO +11. Memory Pressure + +The pressure level notifications can be used to monitor the memory +allocation cost; based on the pressure, applications can implement +different strategies of managing their memory resources. The pressure +levels are defined as following: + +The "low" level means that the system is reclaiming memory for new +allocations. Monitoring this reclaiming activity might be useful for +maintaining cache level. Upon notification, the program (typically +"Activity Manager") might analyze vmstat and act in advance (i.e. +prematurely shutdown unimportant services). + +The "medium" level means that the system is experiencing medium memory +pressure, the system might be making swap, paging out active file caches, +etc. Upon this event applications may decide to further analyze +vmstat/zoneinfo/memcg or internal memory usage statistics and free any +resources that can be easily reconstructed or re-read from a disk. + +The "critical" level means that the system is actively thrashing, it is +about to out of memory (OOM) or even the in-kernel OOM killer is on its +way to trigger. Applications should do whatever they can to help the +system. It might be too late to consult with vmstat or any other +statistics, so it's advisable to take an immediate action. + +The events are propagated upward until the event is handled, i.e. the +events are not pass-through. Here is what this means: for example you have +three cgroups: A->B->C. Now you set up an event listener on cgroups A, B +and C, and suppose group C experiences some pressure. In this situation, +only group C will receive the notification, i.e. groups A and B will not +receive it. This is done to avoid excessive "broadcasting" of messages, +which disturbs the system and which is especially bad if we are low on +memory or thrashing. So, organize the cgroups wisely, or propagate the +events manually (or, ask us to implement the pass-through events, +explaining why would you need them.) + +The file memory.pressure_level is only used to setup an eventfd. To +register a notification, an application must: + +- create an eventfd using eventfd(2); +- open memory.pressure_level; +- write string like "<event_fd> <fd of memory.pressure_level> <level>" + to cgroup.event_control. + +Application will be notified through eventfd when memory pressure is at +the specific level (or higher). Read/write operations to +memory.pressure_level are no implemented. + +Test: + + Here is a small script example that makes a new cgroup, sets up a + memory limit, sets up a notification in the cgroup and then makes child + cgroup experience a critical pressure: + + # cd /sys/fs/cgroup/memory/ + # mkdir foo + # cd foo + # cgroup_event_listener memory.pressure_level low & + # echo 8000000 > memory.limit_in_bytes + # echo 8000000 > memory.memsw.limit_in_bytes + # echo $$ > tasks + # dd if=/dev/zero | read x + + (Expect a bunch of notifications, and eventually, the oom-killer will + trigger.) + +12. TODO 1. Add support for accounting huge pages (as a separate controller) 2. Make per-cgroup scanner reclaim not-shared pages first |