diff options
Diffstat (limited to 'Documentation/cgroups')
| -rw-r--r-- | Documentation/cgroups/blkio-controller.txt | 151 | ||||
| -rw-r--r-- | Documentation/cgroups/cgroups.txt | 4 | ||||
| -rw-r--r-- | Documentation/cgroups/cpusets.txt | 38 | ||||
| -rw-r--r-- | Documentation/cgroups/memcg_test.txt | 2 | ||||
| -rw-r--r-- | Documentation/cgroups/memory.txt | 328 |
5 files changed, 395 insertions, 128 deletions
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt index 630879cd9a42..48e0b21b0059 100644 --- a/Documentation/cgroups/blkio-controller.txt +++ b/Documentation/cgroups/blkio-controller.txt @@ -17,6 +17,9 @@ HOWTO You can do a very simple testing of running two dd threads in two different cgroups. Here is what you can do. +- Enable Block IO controller + CONFIG_BLK_CGROUP=y + - Enable group scheduling in CFQ CONFIG_CFQ_GROUP_IOSCHED=y @@ -54,32 +57,52 @@ cgroups. Here is what you can do. Various user visible config options =================================== -CONFIG_CFQ_GROUP_IOSCHED - - Enables group scheduling in CFQ. Currently only 1 level of group - creation is allowed. - -CONFIG_DEBUG_CFQ_IOSCHED - - Enables some debugging messages in blktrace. Also creates extra - cgroup file blkio.dequeue. - -Config options selected automatically -===================================== -These config options are not user visible and are selected/deselected -automatically based on IO scheduler configuration. - CONFIG_BLK_CGROUP - - Block IO controller. Selected by CONFIG_CFQ_GROUP_IOSCHED. + - Block IO controller. CONFIG_DEBUG_BLK_CGROUP - - Debug help. Selected by CONFIG_DEBUG_CFQ_IOSCHED. + - Debug help. Right now some additional stats file show up in cgroup + if this option is enabled. + +CONFIG_CFQ_GROUP_IOSCHED + - Enables group scheduling in CFQ. Currently only 1 level of group + creation is allowed. Details of cgroup files ======================= - blkio.weight - - Specifies per cgroup weight. - + - Specifies per cgroup weight. This is default weight of the group + on all the devices until and unless overridden by per device rule. + (See blkio.weight_device). Currently allowed range of weights is from 100 to 1000. +- blkio.weight_device + - One can specify per cgroup per device rules using this interface. + These rules override the default value of group weight as specified + by blkio.weight. + + Following is the format. + + #echo dev_maj:dev_minor weight > /path/to/cgroup/blkio.weight_device + Configure weight=300 on /dev/sdb (8:16) in this cgroup + # echo 8:16 300 > blkio.weight_device + # cat blkio.weight_device + dev weight + 8:16 300 + + Configure weight=500 on /dev/sda (8:0) in this cgroup + # echo 8:0 500 > blkio.weight_device + # cat blkio.weight_device + dev weight + 8:0 500 + 8:16 300 + + Remove specific weight for /dev/sda in this cgroup + # echo 8:0 0 > blkio.weight_device + # cat blkio.weight_device + dev weight + 8:16 300 + - blkio.time - disk time allocated to cgroup per device in milliseconds. First two fields specify the major and minor number of the device and @@ -92,13 +115,105 @@ Details of cgroup files third field specifies the number of sectors transferred by the group to/from the device. +- blkio.io_service_bytes + - Number of bytes transferred to/from the disk by the group. These + are further divided by the type of operation - read or write, sync + or async. First two fields specify the major and minor number of the + device, third field specifies the operation type and the fourth field + specifies the number of bytes. + +- blkio.io_serviced + - Number of IOs completed to/from the disk by the group. These + are further divided by the type of operation - read or write, sync + or async. First two fields specify the major and minor number of the + device, third field specifies the operation type and the fourth field + specifies the number of IOs. + +- blkio.io_service_time + - Total amount of time between request dispatch and request completion + for the IOs done by this cgroup. This is in nanoseconds to make it + meaningful for flash devices too. For devices with queue depth of 1, + this time represents the actual service time. When queue_depth > 1, + that is no longer true as requests may be served out of order. This + may cause the service time for a given IO to include the service time + of multiple IOs when served out of order which may result in total + io_service_time > actual time elapsed. This time is further divided by + the type of operation - read or write, sync or async. First two fields + specify the major and minor number of the device, third field + specifies the operation type and the fourth field specifies the + io_service_time in ns. + +- blkio.io_wait_time + - Total amount of time the IOs for this cgroup spent waiting in the + scheduler queues for service. This can be greater than the total time + elapsed since it is cumulative io_wait_time for all IOs. It is not a + measure of total time the cgroup spent waiting but rather a measure of + the wait_time for its individual IOs. For devices with queue_depth > 1 + this metric does not include the time spent waiting for service once + the IO is dispatched to the device but till it actually gets serviced + (there might be a time lag here due to re-ordering of requests by the + device). This is in nanoseconds to make it meaningful for flash + devices too. This time is further divided by the type of operation - + read or write, sync or async. First two fields specify the major and + minor number of the device, third field specifies the operation type + and the fourth field specifies the io_wait_time in ns. + +- blkio.io_merged + - Total number of bios/requests merged into requests belonging to this + cgroup. This is further divided by the type of operation - read or + write, sync or async. + +- blkio.io_queued + - Total number of requests queued up at any given instant for this + cgroup. This is further divided by the type of operation - read or + write, sync or async. + +- blkio.avg_queue_size + - Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. + The average queue size for this cgroup over the entire time of this + cgroup's existence. Queue size samples are taken each time one of the + queues of this cgroup gets a timeslice. + +- blkio.group_wait_time + - Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. + This is the amount of time the cgroup had to wait since it became busy + (i.e., went from 0 to 1 request queued) to get a timeslice for one of + its queues. This is different from the io_wait_time which is the + cumulative total of the amount of time spent by each IO in that cgroup + waiting in the scheduler queue. This is in nanoseconds. If this is + read when the cgroup is in a waiting (for timeslice) state, the stat + will only report the group_wait_time accumulated till the last time it + got a timeslice and will not include the current delta. + +- blkio.empty_time + - Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. + This is the amount of time a cgroup spends without any pending + requests when not being served, i.e., it does not include any time + spent idling for one of the queues of the cgroup. This is in + nanoseconds. If this is read when the cgroup is in an empty state, + the stat will only report the empty_time accumulated till the last + time it had a pending request and will not include the current delta. + +- blkio.idle_time + - Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. + This is the amount of time spent by the IO scheduler idling for a + given cgroup in anticipation of a better request than the exising ones + from other queues/cgroups. This is in nanoseconds. If this is read + when the cgroup is in an idling state, the stat will only report the + idle_time accumulated till the last idle period and will not include + the current delta. + - blkio.dequeue - - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This + - Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. This gives the statistics about how many a times a group was dequeued from service tree of the device. First two fields specify the major and minor number of the device and third field specifies the number of times a group was dequeued from a particular device. +- blkio.reset_stats + - Writing an int to this file will result in resetting all the stats + for that cgroup. + CFQ sysfs tunable ================= /sys/block/<disk>/queue/iosched/group_isolation diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index a1ca5924faff..b34823ff1646 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -339,7 +339,7 @@ To mount a cgroup hierarchy with all available subsystems, type: The "xxx" is not interpreted by the cgroup code, but will appear in /proc/mounts so may be any useful identifying string that you like. -To mount a cgroup hierarchy with just the cpuset and numtasks +To mount a cgroup hierarchy with just the cpuset and memory subsystems, type: # mount -t cgroup -o cpuset,memory hier1 /dev/cgroup @@ -572,7 +572,7 @@ void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, Called when a task attach operation has failed after can_attach() has succeeded. A subsystem whose can_attach() has some side-effects should provide this -function, so that the subsytem can implement a rollback. If not, not necessary. +function, so that the subsystem can implement a rollback. If not, not necessary. This will be called only about subsystems whose can_attach() operation have succeeded. diff --git a/Documentation/cgroups/cpusets.txt b/Documentation/cgroups/cpusets.txt index 4160df82b3f5..51682ab2dd1a 100644 --- a/Documentation/cgroups/cpusets.txt +++ b/Documentation/cgroups/cpusets.txt @@ -42,7 +42,7 @@ Nodes to a set of tasks. In this document "Memory Node" refers to an on-line node that contains memory. Cpusets constrain the CPU and Memory placement of tasks to only -the resources within a tasks current cpuset. They form a nested +the resources within a task's current cpuset. They form a nested hierarchy visible in a virtual file system. These are the essential hooks, beyond what is already present, required to manage dynamic job placement on large systems. @@ -53,11 +53,11 @@ Documentation/cgroups/cgroups.txt. Requests by a task, using the sched_setaffinity(2) system call to include CPUs in its CPU affinity mask, and using the mbind(2) and set_mempolicy(2) system calls to include Memory Nodes in its memory -policy, are both filtered through that tasks cpuset, filtering out any +policy, are both filtered through that task's cpuset, filtering out any CPUs or Memory Nodes not in that cpuset. The scheduler will not schedule a task on a CPU that is not allowed in its cpus_allowed vector, and the kernel page allocator will not allocate a page on a -node that is not allowed in the requesting tasks mems_allowed vector. +node that is not allowed in the requesting task's mems_allowed vector. User level code may create and destroy cpusets by name in the cgroup virtual file system, manage the attributes and permissions of these @@ -121,9 +121,9 @@ Cpusets extends these two mechanisms as follows: - Each task in the system is attached to a cpuset, via a pointer in the task structure to a reference counted cgroup structure. - Calls to sched_setaffinity are filtered to just those CPUs - allowed in that tasks cpuset. + allowed in that task's cpuset. - Calls to mbind and set_mempolicy are filtered to just - those Memory Nodes allowed in that tasks cpuset. + those Memory Nodes allowed in that task's cpuset. - The root cpuset contains all the systems CPUs and Memory Nodes. - For any cpuset, one can define child cpusets containing a subset @@ -141,11 +141,11 @@ into the rest of the kernel, none in performance critical paths: - in init/main.c, to initialize the root cpuset at system boot. - in fork and exit, to attach and detach a task from its cpuset. - in sched_setaffinity, to mask the requested CPUs by what's - allowed in that tasks cpuset. + allowed in that task's cpuset. - in sched.c migrate_live_tasks(), to keep migrating tasks within the CPUs allowed by their cpuset, if possible. - in the mbind and set_mempolicy system calls, to mask the requested - Memory Nodes by what's allowed in that tasks cpuset. + Memory Nodes by what's allowed in that task's cpuset. - in page_alloc.c, to restrict memory to allowed nodes. - in vmscan.c, to restrict page recovery to the current cpuset. @@ -155,7 +155,7 @@ new system calls are added for cpusets - all support for querying and modifying cpusets is via this cpuset file system. The /proc/<pid>/status file for each task has four added lines, -displaying the tasks cpus_allowed (on which CPUs it may be scheduled) +displaying the task's cpus_allowed (on which CPUs it may be scheduled) and mems_allowed (on which Memory Nodes it may obtain memory), in the two formats seen in the following example: @@ -323,17 +323,17 @@ stack segment pages of a task. By default, both kinds of memory spreading are off, and memory pages are allocated on the node local to where the task is running, -except perhaps as modified by the tasks NUMA mempolicy or cpuset +except perhaps as modified by the task's NUMA mempolicy or cpuset configuration, so long as sufficient free memory pages are available. When new cpusets are created, they inherit the memory spread settings of their parent. Setting memory spreading causes allocations for the affected page -or slab caches to ignore the tasks NUMA mempolicy and be spread +or slab caches to ignore the task's NUMA mempolicy and be spread instead. Tasks using mbind() or set_mempolicy() calls to set NUMA mempolicies will not notice any change in these calls as a result of -their containing tasks memory spread settings. If memory spreading +their containing task's memory spread settings. If memory spreading is turned off, then the currently specified NUMA mempolicy once again applies to memory page allocations. @@ -357,7 +357,7 @@ pages from the node returned by cpuset_mem_spread_node(). The cpuset_mem_spread_node() routine is also simple. It uses the value of a per-task rotor cpuset_mem_spread_rotor to select the next -node in the current tasks mems_allowed to prefer for the allocation. +node in the current task's mems_allowed to prefer for the allocation. This memory placement policy is also known (in other contexts) as round-robin or interleave. @@ -594,7 +594,7 @@ is attached, is subtle. If a cpuset has its Memory Nodes modified, then for each task attached to that cpuset, the next time that the kernel attempts to allocate a page of memory for that task, the kernel will notice the change -in the tasks cpuset, and update its per-task memory placement to +in the task's cpuset, and update its per-task memory placement to remain within the new cpusets memory placement. If the task was using mempolicy MPOL_BIND, and the nodes to which it was bound overlap with its new cpuset, then the task will continue to use whatever subset @@ -603,13 +603,13 @@ was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed in the new cpuset, then the task will be essentially treated as if it was MPOL_BIND bound to the new cpuset (even though its NUMA placement, as queried by get_mempolicy(), doesn't change). If a task is moved -from one cpuset to another, then the kernel will adjust the tasks +from one cpuset to another, then the kernel will adjust the task's memory placement, as above, the next time that the kernel attempts to allocate a page of memory for that task. If a cpuset has its 'cpuset.cpus' modified, then each task in that cpuset will have its allowed CPU placement changed immediately. Similarly, -if a tasks pid is written to another cpusets 'cpuset.tasks' file, then its +if a task's pid is written to another cpusets 'cpuset.tasks' file, then its allowed CPU placement is changed immediately. If such a task had been bound to some subset of its cpuset using the sched_setaffinity() call, the task will be allowed to run on any CPU allowed in its new cpuset, @@ -626,16 +626,16 @@ cpusets memory placement policy 'cpuset.mems' subsequently changes. If the cpuset flag file 'cpuset.memory_migrate' is set true, then when tasks are attached to that cpuset, any pages that task had allocated to it on nodes in its previous cpuset are migrated -to the tasks new cpuset. The relative placement of the page within +to the task's new cpuset. The relative placement of the page within the cpuset is preserved during these migration operations if possible. For example if the page was on the second valid node of the prior cpuset then the page will be placed on the second valid node of the new cpuset. -Also if 'cpuset.memory_migrate' is set true, then if that cpusets +Also if 'cpuset.memory_migrate' is set true, then if that cpuset's 'cpuset.mems' file is modified, pages allocated to tasks in that cpuset, that were on nodes in the previous setting of 'cpuset.mems', will be moved to nodes in the new setting of 'mems.' -Pages that were not in the tasks prior cpuset, or in the cpusets +Pages that were not in the task's prior cpuset, or in the cpuset's prior 'cpuset.mems' setting, will not be moved. There is an exception to the above. If hotplug functionality is used @@ -655,7 +655,7 @@ There is a second exception to the above. GFP_ATOMIC requests are kernel internal allocations that must be satisfied, immediately. The kernel may drop some request, in rare cases even panic, if a GFP_ATOMIC alloc fails. If the request cannot be satisfied within -the current tasks cpuset, then we relax the cpuset, and look for +the current task's cpuset, then we relax the cpuset, and look for memory anywhere we can find it. It's better to violate the cpuset than stress the kernel. diff --git a/Documentation/cgroups/memcg_test.txt b/Documentation/cgroups/memcg_test.txt index f7f68b2ac199..b7eececfb195 100644 --- a/Documentation/cgroups/memcg_test.txt +++ b/Documentation/cgroups/memcg_test.txt @@ -244,7 +244,7 @@ Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y. we have to check if OLDPAGE/NEWPAGE is a valid page after commit(). 8. LRU - Each memcg has its own private LRU. Now, it's handling is under global + Each memcg has its own private LRU. Now, its handling is under global VM's control (means that it's handled under global zone->lru_lock). Almost all routines around memcg's LRU is called by global LRU's list management functions under zone->lru_lock(). diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 3a6aecd078ba..7781857dc940 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -1,18 +1,15 @@ Memory Resource Controller NOTE: The Memory Resource Controller has been generically been referred -to as the memory controller in this document. Do not confuse memory controller -used here with the memory controller that is used in hardware. + to as the memory controller in this document. Do not confuse memory + controller used here with the memory controller that is used in hardware. -Salient features - -a. Enable control of Anonymous, Page Cache (mapped and unmapped) and - Swap Cache memory pages. -b. The infrastructure allows easy addition of other types of memory to control -c. Provides *zero overhead* for non memory controller users -d. Provides a double LRU: global memory pressure causes reclaim from the - global LRU; a cgroup on hitting a limit, reclaims from the per - cgroup LRU +(For editors) +In this document: + When we mention a cgroup (cgroupfs's directory) with memory controller, + we call it "memory cgroup". When you see git-log and source code, you'll + see patch's title and function names tend to use "memcg". + In this document, we avoid using it. Benefits and Purpose of the memory controller @@ -33,6 +30,45 @@ d. A CD/DVD burner could control the amount of memory used by the e. There are several other use cases, find one or use the controller just for fun (to learn and hack on the VM subsystem). +Current Status: linux-2.6.34-mmotm(development version of 2010/April) + +Features: + - accounting anonymous pages, file caches, swap caches usage and limiting them. + - private LRU and reclaim routine. (system's global LRU and private LRU + work independently from each other) + - optionally, memory+swap usage can be accounted and limited. + - hierarchical accounting + - soft limit + - moving(recharging) account at moving a task is selectable. + - usage threshold notifier + - oom-killer disable knob and oom-notifier + - Root cgroup has no limit controls. + + Kernel memory and Hugepages are not under control yet. We just manage + pages on LRU. To add more controls, we have to take care of performance. + +Brief summary of control files. + + tasks # attach a task(thread) and show list of threads + cgroup.procs # show list of processes + cgroup.event_control # an interface for event_fd() + memory.usage_in_bytes # show current memory(RSS+Cache) usage. + memory.memsw.usage_in_bytes # show current memory+Swap usage + memory.limit_in_bytes # set/show limit of memory usage + memory.memsw.limit_in_bytes # set/show limit of memory+Swap usage + memory.failcnt # show the number of memory usage hits limits + memory.memsw.failcnt # show the number of memory+Swap hits limits + memory.max_usage_in_bytes # show max memory usage recorded + memory.memsw.usage_in_bytes # show max memory+Swap usage recorded + memory.soft_limit_in_bytes # set/show soft limit of memory usage + memory.stat # show various statistics + memory.use_hierarchy # set/show hierarchical account enabled + memory.force_empty # trigger forced move charge to parent + memory.swappiness # set/show swappiness parameter of vmscan + (See sysctl's vm.swappiness) + memory.move_charge_at_immigrate # set/show controls of moving charges + memory.oom_control # set/show oom controls. + 1. History The memory controller has a long history. A request for comments for the memory @@ -106,14 +142,14 @@ the necessary data structures and check if the cgroup that is being charged is over its limit. If it is then reclaim is invoked on the cgroup. More details can be found in the reclaim section of this document. If everything goes well, a page meta-data-structure called page_cgroup is -allocated and associated with the page. This routine also adds the page to -the per cgroup LRU. +updated. page_cgroup has its own LRU on cgroup. +(*) page_cgroup structure is allocated at boot/memory-hotplug time. 2.2.1 Accounting details All mapped anon pages (RSS) and cache pages (Page Cache) are accounted. -(some pages which never be reclaimable and will not be on global LRU - are not accounted. we just accounts pages under usual vm management.) +Some pages which are never reclaimable and will not be on the global LRU +are not accounted. We just account pages under usual VM management. RSS pages are accounted at page_fault unless they've already been accounted for earlier. A file page will be accounted for as Page Cache when it's @@ -121,12 +157,19 @@ inserted into inode (radix-tree). While it's mapped into the page tables of processes, duplicate accounting is carefully avoided. A RSS page is unaccounted when it's fully unmapped. A PageCache page is -unaccounted when it's removed from radix-tree. +unaccounted when it's removed from radix-tree. Even if RSS pages are fully +unmapped (by kswapd), they may exist as SwapCache in the system until they +are really freed. Such SwapCaches also also accounted. +A swapped-in page is not accounted until it's mapped. + +Note: The kernel does swapin-readahead and read multiple swaps at once. +This means swapped-in pages may contain pages for other tasks than a task +causing page fault. So, we avoid accounting at swap-in I/O. At page migration, accounting information is kept. -Note: we just account pages-on-lru because our purpose is to control amount -of used pages. not-on-lru pages are tend to be out-of-control from vm view. +Note: we just account pages-on-LRU because our purpose is to control amount +of used pages; not-on-LRU pages tend to be out-of-control from VM view. 2.3 Shared Page Accounting @@ -143,6 +186,7 @@ caller of swapoff rather than the users of shmem. 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) + Swap Extension allows you to record charge for swap. A swapped-in page is charged back to original page allocator if possible. @@ -150,13 +194,20 @@ When swap is accounted, following files are added. - memory.memsw.usage_in_bytes. - memory.memsw.limit_in_bytes. -usage of mem+swap is limited by memsw.limit_in_bytes. +memsw means memory+swap. Usage of memory+swap is limited by +memsw.limit_in_bytes. -* why 'mem+swap' rather than swap. +Example: Assume a system with 4G of swap. A task which allocates 6G of memory +(by mistake) under 2G memory limitation will use all swap. +In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap. +By using memsw limit, you can avoid system OOM which can be caused by swap +shortage. + +* why 'memory+swap' rather than swap. The global LRU(kswapd) can swap out arbitrary pages. Swap-out means to move account from memory to swap...there is no change in usage of -mem+swap. In other words, when we want to limit the usage of swap without -affecting global LRU, mem+swap limit is better than just limiting swap from +memory+swap. In other words, when we want to limit the usage of swap without +affecting global LRU, memory+swap limit is better than just limiting swap from OS point of view. * What happens when a cgroup hits memory.memsw.limit_in_bytes @@ -168,12 +219,12 @@ it by cgroup. 2.5 Reclaim -Each cgroup maintains a per cgroup LRU that consists of an active -and inactive list. When a cgroup goes over its limit, we first try +Each cgroup maintains a per cgroup LRU which has the same structure as +global VM. When a cgroup goes over its limit, we first try to reclaim memory from the cgroup so as to make space for the new pages that the cgroup has touched. If the reclaim is unsuccessful, an OOM routine is invoked to select and kill the bulkiest task in the -cgroup. +cgroup. (See 10. OOM Control below.) The reclaim algorithm has not been modified for cgroups, except that pages that are selected for reclaiming come from the per cgroup LRU @@ -184,13 +235,22 @@ limits on the root cgroup. Note2: When panic_on_oom is set to "2", the whole system will panic. -2. Locking +When oom event notifier is registered, event will be delivered. +(See oom_control section) + +2.6 Locking -The memory controller uses the following hierarchy + lock_page_cgroup()/unlock_page_cgroup() should not be called under + mapping->tree_lock. -1. zone->lru_lock is used for selecting pages to be isolated -2. mem->per_zone->lru_lock protects the per cgroup LRU (per zone) -3. lock_page_cgroup() is used to protect page->page_cgroup + Other lock order is following: + PG_locked. + mm->page_table_lock + zone->lru_lock + lock_page_cgroup. + In many cases, just lock_page_cgroup() is called. + per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by + zone->lru_lock, it has no lock of its own. 3. User Interface @@ -199,6 +259,7 @@ The memory controller uses the following hierarchy a. Enable CONFIG_CGROUPS b. Enable CONFIG_RESOURCE_COUNTERS c. Enable CONFIG_CGROUP_MEM_RES_CTLR +d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension) 1. Prepare the cgroups # mkdir -p /cgroups @@ -206,31 +267,28 @@ c. Enable CONFIG_CGROUP_MEM_RES_CTLR 2. Make the new group and move bash into it # mkdir /cgroups/0 -# echo $$ > /cgroups/0/tasks +# echo $$ > /cgroups/0/tasks -Since now we're in the 0 cgroup, -We can alter the memory limit: +Since now we're in the 0 cgroup, we can alter the memory limit: # echo 4M > /cgroups/0/memory.limit_in_bytes NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo, -mega or gigabytes. +mega or gigabytes. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes, Gibibytes.) + NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited). NOTE: We cannot set limits on the root cgroup any more. # cat /cgroups/0/memory.limit_in_bytes 4194304 -NOTE: The interface has now changed to display the usage in bytes -instead of pages - We can check the usage: # cat /cgroups/0/memory.usage_in_bytes 1216512 A successful write to this file does not guarantee a successful set of -this limit to the value written into the file. This can be due to a +this limit to the value written into the file. This can be due to a number of factors, such as rounding up to page boundaries or the total -availability of memory on the system. The user is required to re-read +availability of memory on the system. The user is required to re-read this file after a write to guarantee the value committed by the kernel. # echo 1 > memory.limit_in_bytes @@ -245,15 +303,23 @@ caches, RSS and Active pages/Inactive pages are shown. 4. Testing -Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11]. -Apart from that v6 has been tested with several applications and regular -daily use. The controller has also been tested on the PPC64, x86_64 and -UML platforms. +For testing features and implementation, see memcg_test.txt. + +Performance test is also important. To see pure memory controller's overhead, +testing on tmpfs will give you good numbers of small overheads. +Example: do kernel make on tmpfs. + +Page-fault scalability is also important. At measuring parallel +page fault test, multi-process test may be better than multi-thread +test because it has noise of shared objects/status. + +But the above two are testing extreme situations. +Trying usual test under memory controller is always helpful. 4.1 Troubleshooting Sometimes a user might find that the application under a cgroup is -terminated. There are several causes for this: +terminated by OOM killer. There are several causes for this: 1. The cgroup limit is too low (just too low to do anything useful) 2. The user is using anonymous memory and swap is turned off or too low @@ -261,23 +327,29 @@ terminated. There are several causes for this: A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of some of the pages cached in the cgroup (page cache pages). +To know what happens, disable OOM_Kill by 10. OOM Control(see below) and +seeing what happens will be helpful. + 4.2 Task migration -When a task migrates from one cgroup to another, it's charge is not +When a task migrates from one cgroup to another, its charge is not carried forward by default. The pages allocated from the original cgroup still remain charged to it, the charge is dropped when the page is freed or reclaimed. -Note: You can move charges of a task along with task migration. See 8. +You can move charges of a task along with task migration. +See 8. "Move charges at task migration" 4.3 Removing a cgroup A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a cgroup might have some charge associated with it, even though all -tasks have migrated away from it. -Such charges are freed(at default) or moved to its parent. When moved, -both of RSS and CACHES are moved to parent. -If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also. +tasks have migrated away from it. (because we charge against pages, not +against tasks.) + +Such charges are freed or moved to their parent. At moving, both of RSS +and CACHES are moved to parent. +rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also. Charges recorded in swap information is not updated at removal of cgroup. Recorded information is discarded and a cgroup which uses swap (swapcache) @@ -293,10 +365,10 @@ will be charged as a new owner of it. # echo 0 > memory.force_empty - Almost all pages tracked by this memcg will be unmapped and freed. Some of - pages cannot be freed because it's locked or in-use. Such pages are moved - to parent and this cgroup will be empty. But this may return -EBUSY in - some too busy case. + Almost all pages tracked by this memory cgroup will be unmapped and freed. + Some pages cannot be freed because they are locked or in-use. Such pages are + moved to parent and this cgroup will be empty. This may return -EBUSY if + VM is too busy to free/move all pages immediately. Typical use case of this interface is that calling this before rmdir(). Because rmdir() moves all pages to parent, some out-of-use page caches can be @@ -306,19 +378,41 @@ will be charged as a new owner of it. memory.stat file includes following statistics +# per-memory cgroup local status cache - # of bytes of page cache memory. rss - # of bytes of anonymous and swap cache memory. +mapped_file - # of bytes of mapped file (includes tmpfs/shmem) pgpgin - # of pages paged in (equivalent to # of charging events). pgpgout - # of pages paged out (equivalent to # of uncharging events). -active_anon - # of bytes of anonymous and swap cache memory on active - lru list. +swap - # of bytes of swap usage inactive_anon - # of bytes of anonymous memory and swap cache memory on - inactive lru list. -active_file - # of bytes of file-backed memory on active lru list. -inactive_file - # of bytes of file-backed memory on inactive lru list. + LRU list. +active_anon - # of bytes of anonymous and swap cache memory on active + inactive LRU list. +inactive_file - # of bytes of file-backed memory on inactive LRU list. +active_file - # of bytes of file-backed memory on active LRU list. unevictable - # of bytes of memory that cannot be reclaimed (mlocked etc). -The following additional stats are dependent on CONFIG_DEBUG_VM. +# status considering hierarchy (see memory.use_hierarchy settings) + +hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy + under which the memory cgroup is +hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to + hierarchy under which memory cgroup is. + +total_cache - sum of all children's "cache" +total_rss - sum of all children's "rss" +total_mapped_file - sum of all children's "cache" +total_pgpgin - sum of all children's "pgpgin" +total_pgpgout - sum of all children's "pgpgout" +total_swap - sum of all children's "swap" +total_inactive_anon - sum of all children's "inactive_anon" +total_active_anon - sum of all children's "active_anon" +total_inactive_file - sum of all children's "inactive_file" +total_active_file - sum of all children's "active_file" +total_unevictable - sum of all children's "unevictable" + +# The following additional stats are dependent on CONFIG_DEBUG_VM. inactive_ratio - VM internal parameter. (see mm/page_alloc.c) recent_rotated_anon - VM internal parameter. (see mm/vmscan.c) @@ -327,24 +421,37 @@ recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) recent_scanned_file - VM internal parameter. (see mm/vmscan.c) Memo: - recent_rotated means recent frequency of lru rotation. - recent_scanned means recent # of scans to lru. + recent_rotated means recent frequency of LRU rotation. + recent_scanned means recent # of scans to LRU. showing for better debug please see the code for meanings. Note: Only anonymous and swap cache memory is listed as part of 'rss' stat. This should not be confused with the true 'resident set size' or the - amount of physical memory used by the cgroup. Per-cgroup rss - accounting is not done yet. + amount of physical memory used by the cgroup. + 'rss + file_mapped" will give you resident set size of cgroup. + (Note: file and shmem may be shared among other cgroups. In that case, + file_mapped is accounted only when the memory cgroup is owner of page + cache.) 5.3 swappiness - Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. - Following cgroups' swappiness can't be changed. - - root cgroup (uses /proc/sys/vm/swappiness). - - a cgroup which uses hierarchy and it has child cgroup. - - a cgroup which uses hierarchy and not the root of hierarchy. +Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. +Following cgroups' swappiness can't be changed. +- root cgroup (uses /proc/sys/vm/swappiness). +- a cgroup which uses hierarchy and it has other cgroup(s) below it. +- a cgroup which uses hierarchy and not the root of hierarchy. + +5.4 failcnt + +A memory cgroup provides memory.failcnt and memory.memsw.failcnt files. +This failcnt(== failure count) shows the number of times that a usage counter +hit its limit. When a memory cgroup hits a limit, failcnt increases and +memory under it will be reclaimed. + +You can reset failcnt by writing 0 to failcnt file. +# echo 0 > .../memory.failcnt 6. Hierarchy support @@ -363,13 +470,13 @@ hierarchy In the diagram above, with hierarchical accounting enabled, all memory usage of e, is accounted to its ancestors up until the root (i.e, c and root), -that has memory.use_hierarchy enabled. If one of the ancestors goes over its +that has memory.use_hierarchy enabled. If one of the ancestors goes over its limit, the reclaim algorithm reclaims from the tasks in the ancestor and the children of the ancestor. 6.1 Enabling hierarchical accounting and reclaim -The memory controller by default disables the hierarchy feature. Support +A memory cgroup by default disables the hierarchy feature. Support can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup # echo 1 > memory.use_hierarchy @@ -379,10 +486,10 @@ The feature can be disabled by # echo 0 > memory.use_hierarchy NOTE1: Enabling/disabling will fail if the cgroup already has other -cgroups created below it. + cgroups created below it. NOTE2: When panic_on_oom is set to "2", the whole system will panic in -case of an oom event in any cgroup. + case of an OOM event in any cgroup. 7. Soft limits @@ -392,7 +499,7 @@ is to allow control groups to use as much of the memory as needed, provided a. There is no memory contention b. They do not exceed their hard limit -When the system detects memory contention or low memory control groups +When the system detects memory contention or low memory, control groups are pushed back to their soft limits. If the soft limit of each control group is very high, they are pushed back as much as possible to make sure that one control group does not starve the others of memory. @@ -406,7 +513,7 @@ it gets invoked from balance_pgdat (kswapd). 7.1 Interface Soft limits can be setup by using the following commands (in this example we -assume a soft limit of 256 megabytes) +assume a soft limit of 256 MiB) # echo 256M > memory.soft_limit_in_bytes @@ -442,7 +549,7 @@ Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread Note: If we cannot find enough space for the task in the destination cgroup, we try to make space by reclaiming memory. Task migration may fail if we cannot make enough space. -Note: It can take several seconds if you move charges in giga bytes order. +Note: It can take several seconds if you move charges much. And if you want disable it again: @@ -451,21 +558,27 @@ And if you want disable it again: 8.2 Type of charges which can be move Each bits of move_charge_at_immigrate has its own meaning about what type of -charges should be moved. +charges should be moved. But in any cases, it must be noted that an account of +a page or a swap can be moved only when it is charged to the task's current(old) +memory cgroup. bit | what type of charges would be moved ? -----+------------------------------------------------------------------------ 0 | A charge of an anonymous page(or swap of it) used by the target task. | Those pages and swaps must be used only by the target task. You must | enable Swap Extension(see 2.4) to enable move of swap charges. - -Note: Those pages and swaps must be charged to the old cgroup. -Note: More type of pages(e.g. file cache, shmem,) will be supported by other - bits in future. + -----+------------------------------------------------------------------------ + 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) + | and swaps of tmpfs file) mmapped by the target task. Unlike the case of + | anonymous pages, file pages(and swaps) in the range mmapped by the task + | will be moved even if the task hasn't done page fault, i.e. they might + | not be the task's "RSS", but other task's "RSS" that maps the same file. + | And mapcount of the page is ignored(the page can be moved even if + | page_mapcount(page) > 1). You must enable Swap Extension(see 2.4) to + | enable move of swap charges. 8.3 TODO -- Add support for other types of pages(e.g. file cache, shmem, etc.). - Implement madvise(2) to let users decide the vma to be moved or not to be moved. - All of moving charge operations are done under cgroup_mutex. It's not good @@ -473,22 +586,61 @@ Note: More type of pages(e.g. file cache, shmem,) will be supported by other 9. Memory thresholds -Memory controler implements memory thresholds using cgroups notification +Memory cgroup implements memory thresholds using cgroups notification API (see cgroups.txt). It allows to register multiple memory and memsw thresholds and gets notifications when it crosses. To register a threshold application need: - - create an eventfd using eventfd(2); - - open memory.usage_in_bytes or memory.memsw.usage_in_bytes; - - write string like "<event_fd> <memory.usage_in_bytes> <threshold>" to - cgroup.event_control. +- create an eventfd using eventfd(2); +- open memory.usage_in_bytes or memory.memsw.usage_in_bytes; +- write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to + cgroup.event_control. Application will be notified through eventfd when memory usage crosses threshold in any direction. It's applicable for root and non-root cgroup. -10. TODO +10. OOM Control + +memory.oom_control file is for OOM notification and other controls. + +Memory cgroup implements OOM notifier using cgroup notification +API (See cgroups.txt). It allows to register multiple OOM notification +delivery and gets notification when OOM happens. + +To register a notifier, application need: + - create an eventfd using eventfd(2) + - open memory.oom_control file + - write string like "<event_fd> <fd of memory.oom_control>" to + cgroup.event_control + +Application will be notified through eventfd when OOM happens. +OOM notification doesn't work for root cgroup. + +You can disable OOM-killer by writing "1" to memory.oom_control file, as: + + #echo 1 > memory.oom_control + +This operation is only allowed to the top cgroup of sub-hierarchy. +If OOM-killer is disabled, tasks under cgroup will hang/sleep +in memory cgroup's OOM-waitqueue when they request accountable memory. + +For running them, you have to relax the memory cgroup's OOM status by + * enlarge limit or reduce usage. +To reduce usage, + * kill some tasks. + * move some tasks to other group with account migration. + * remove some files (on tmpfs?) + +Then, stopped tasks will work again. + +At reading, current status of OOM is shown. + oom_kill_disable 0 or 1 (if 1, oom-killer is disabled) + under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may + be stopped.) + +11. TODO 1. Add support for accounting huge pages (as a separate controller) 2. Make per-cgroup scanner reclaim not-shared pages first |
