Lines Matching +full:memory +full:- +full:controller
1 Memory Resource Controller
8 NOTE: The Memory Resource Controller has generically been referred to as the
9 memory controller in this document. Do not confuse memory controller
10 used here with the memory controller that is used in hardware.
14 When we mention a cgroup (cgroupfs's directory) with memory controller,
15 we call it "memory cgroup". When you see git-log and source code, you'll
19 Benefits and Purpose of the memory controller
21 The memory controller isolates the memory behaviour of a group of tasks
23 uses of the memory controller. The memory controller can be used to
26 Memory-hungry applications can be isolated and limited to a smaller
27 amount of memory.
28 b. Create a cgroup with a limited amount of memory; this can be used
30 c. Virtualization solutions can control the amount of memory they want
32 d. A CD/DVD burner could control the amount of memory used by the
34 of available memory.
35 e. There are several other use cases; find one or use the controller just
38 Current Status: linux-2.6.34-mmotm(development version of 2010/April)
41 - accounting anonymous pages, file caches, swap caches usage and limiting them.
42 - pages are linked to per-memcg LRU exclusively, and there is no global LRU.
43 - optionally, memory+swap usage can be accounted and limited.
44 - hierarchical accounting
45 - soft limit
46 - moving (recharging) account at moving a task is selectable.
47 - usage threshold notifier
48 - memory pressure notifier
49 - oom-killer disable knob and oom-notifier
50 - Root cgroup has no limit controls.
52 Kernel memory support is a work in progress, and the current version provides
60 memory.usage_in_bytes # show current usage for memory
62 memory.memsw.usage_in_bytes # show current usage for memory+Swap
64 memory.limit_in_bytes # set/show limit of memory usage
65 memory.memsw.limit_in_bytes # set/show limit of memory+Swap usage
66 memory.failcnt # show the number of memory usage hits limits
67 memory.memsw.failcnt # show the number of memory+Swap hits limits
68 memory.max_usage_in_bytes # show max memory usage recorded
69 memory.memsw.max_usage_in_bytes # show max memory+Swap usage recorded
70 memory.soft_limit_in_bytes # set/show soft limit of memory usage
71 memory.stat # show various statistics
72 memory.use_hierarchy # set/show hierarchical account enabled
73 memory.force_empty # trigger forced move charge to parent
74 memory.pressure_level # set memory pressure notifications
75 memory.swappiness # set/show swappiness parameter of vmscan
77 memory.move_charge_at_immigrate # set/show controls of moving charges
78 memory.oom_control # set/show oom controls.
79 memory.numa_stat # show the number of memory usage per numa node
81 memory.kmem.limit_in_bytes # set/show hard limit for kernel memory
82 memory.kmem.usage_in_bytes # show current kernel memory allocation
83 memory.kmem.failcnt # show the number of kernel memory usage hits limits
84 memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded
86 memory.kmem.tcp.limit_in_bytes # set/show hard limit for tcp buf memory
87 memory.kmem.tcp.usage_in_bytes # show current tcp buf memory allocation
88 memory.kmem.tcp.failcnt # show the number of tcp buf memory usage hits limits
89 memory.kmem.tcp.max_usage_in_bytes # show max tcp buf memory usage recorded
93 The memory controller has a long history. A request for comments for the memory
94 controller was posted by Balbir Singh [1]. At the time the RFC was posted
95 there were several implementations for memory control. The goal of the
97 for memory control. The first RSS controller was posted by Balbir Singh[2]
99 RSS controller. At OLS, at the resource management BoF, everyone suggested
101 to allow user space handling of OOM. The current memory controller is
105 2. Memory Control
107 Memory is a unique resource in the sense that it is present in a limited
110 memory, the same physical memory needs to be reused to accomplish the task.
112 The memory controller implementation has been divided into phases. These
115 1. Memory controller
116 2. mlock(2) controller
117 3. Kernel user memory accounting and slab control
118 4. user mappings length controller
120 The memory controller is the first controller developed.
125 page_counter tracks the current memory usage and limit of the group of
126 processes associated with the controller. Each cgroup has a memory controller
131 +--------------------+
134 +--------------------+
137 +---------------+ | +---------------+
140 +---------------+ | +---------------+
142 + --------------+
144 +---------------+ +------+--------+
145 | page +----------> page_cgroup|
147 +---------------+ +---------------+
152 Figure 1 shows the important aspects of the controller
163 If everything goes well, a page meta-data-structure called page_cgroup is
165 (*) page_cgroup structure is allocated at boot/memory-hotplug time.
175 inserted into inode (radix-tree). While it's mapped into the page tables of
179 unaccounted when it's removed from radix-tree. Even if RSS pages are fully
182 A swapped-in page is not accounted until it's mapped.
184 Note: The kernel does swapin-readahead and reads multiple swaps at once.
185 This means swapped-in pages may contain pages for other tasks than a task
186 causing page fault. So, we avoid accounting at swap-in I/O.
190 Note: we just account pages-on-LRU because our purpose is to control amount
191 of used pages; not-on-LRU pages tend to be out-of-control from VM view.
199 the cgroup that brought it in -- this will happen on memory pressure).
205 When you do swapoff and make swapped-out pages of shmem(tmpfs) to
206 be backed into memory in force, charges for pages are accounted against the
211 Swap Extension allows you to record charge for swap. A swapped-in page is
215 - memory.memsw.usage_in_bytes.
216 - memory.memsw.limit_in_bytes.
218 memsw means memory+swap. Usage of memory+swap is limited by
221 Example: Assume a system with 4G of swap. A task which allocates 6G of memory
222 (by mistake) under 2G memory limitation will use all swap.
227 * why 'memory+swap' rather than swap.
228 The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
229 to move account from memory to swap...there is no change in usage of
230 memory+swap. In other words, when we want to limit the usage of swap without
231 affecting global LRU, memory+swap limit is better than just limiting swap from
234 * What happens when a cgroup hits memory.memsw.limit_in_bytes
235 When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
236 in this cgroup. Then, swap-out will not be done by cgroup routine and file
237 caches are dropped. But as mentioned above, global LRU can do swapout memory
238 from it for sanity of the system's memory management state. You can't forbid
245 to reclaim memory from the cgroup so as to make space for the new
251 pages that are selected for reclaiming come from the per-cgroup LRU
269 mm->page_table_lock
273 per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
276 2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
278 With the Kernel memory extension, the Memory Controller is able to limit
279 the amount of kernel memory used by the system. Kernel memory is fundamentally
280 different than user memory, since it can't be swapped out, which makes it
283 Kernel memory accounting is enabled for all memory cgroups by default. But
284 it can be disabled system-wide by passing cgroup.memory=nokmem to the kernel
285 at boot time. In this case, kernel memory will not be accounted at all.
287 Kernel memory limits are not imposed for the root cgroup. Usage for the root
288 cgroup may or may not be accounted. The memory used is accumulated into
289 memory.kmem.usage_in_bytes, or in a separate counter when it makes sense.
294 Currently no soft limit is implemented for kernel memory. It is future work
297 2.7.1 Current Kernel Memory resources accounted
300 kernel memory, we prevent new processes from being created when the kernel
301 memory usage is too high.
310 * sockets memory pressure: some sockets protocols have memory pressure
311 thresholds. The Memory Controller allows them to be controlled individually
314 * tcp memory pressure: sockets memory pressure for the tcp protocol.
318 Because the "kmem" counter is fed to the main user counter, kernel memory can
319 never be limited completely independently of user memory. Say "U" is the user
325 accounting. Kernel memory is completely ignored.
328 Kernel memory is a subset of the user memory. This setup is useful in
329 deployments where the total amount of memory per-cgroup is overcommited.
330 Overcommiting kernel memory limits is definitely not recommended, since the
331 box can still run out of non-reclaimable memory.
333 never greater than the total memory, and freely set U at the cost of his
335 WARNING: In the current implementation, memory reclaim will NOT be
341 triggered for the cgroup for both kinds of memory. This setup gives the
342 admin a unified view of memory, and it is also useful for people who just
343 want to track kernel memory usage.
355 # mount -t tmpfs none /sys/fs/cgroup
356 # mkdir /sys/fs/cgroup/memory
357 # mount -t cgroup none /sys/fs/cgroup/memory -o memory
360 # mkdir /sys/fs/cgroup/memory/0
361 # echo $$ > /sys/fs/cgroup/memory/0/tasks
363 Since now we're in the 0 cgroup, we can alter the memory limit:
364 # echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes
369 NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited).
372 # cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
376 # cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
382 availability of memory on the system. The user is required to re-read
385 # echo 1 > memory.limit_in_bytes
386 # cat memory.limit_in_bytes
389 The memory.failcnt field gives the number of times that the cgroup limit was
392 The memory.stat file gives accounting information. Now, the number of
399 Performance test is also important. To see pure memory controller's overhead,
403 Page-fault scalability is also important. At measuring parallel
404 page fault test, multi-process test may be better than multi-thread
408 Trying usual test under memory controller is always helpful.
416 2. The user is using anonymous memory and swap is turned off or too low
454 memory.force_empty interface is provided to make cgroup's memory usage empty.
457 # echo 0 > memory.force_empty
462 Because rmdir() moves all pages to parent, some out-of-use page caches can be
465 Also, note that when memory.kmem.limit_in_bytes is set the charges due to
468 memory.kmem.usage_in_bytes == memory.usage_in_bytes.
474 memory.stat file includes following statistics
476 # per-memory cgroup local status
477 cache - # of bytes of page cache memory.
478 rss - # of bytes of anonymous and swap cache memory (includes
480 rss_huge - # of bytes of anonymous transparent hugepages.
481 mapped_file - # of bytes of mapped file (includes tmpfs/shmem)
482 pgpgin - # of charging events to the memory cgroup. The charging
485 pgpgout - # of uncharging events to the memory cgroup. The uncharging
487 swap - # of bytes of swap usage
488 dirty - # of bytes that are waiting to get written back to the disk.
489 writeback - # of bytes of file/anon cache that are queued for syncing to
491 inactive_anon - # of bytes of anonymous and swap cache memory on inactive
493 active_anon - # of bytes of anonymous and swap cache memory on active
495 inactive_file - # of bytes of file-backed memory on inactive LRU list.
496 active_file - # of bytes of file-backed memory on active LRU list.
497 unevictable - # of bytes of memory that cannot be reclaimed (mlocked etc).
499 # status considering hierarchy (see memory.use_hierarchy settings)
501 hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy
502 under which the memory cgroup is
503 hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to
504 hierarchy under which memory cgroup is.
506 total_<counter> - # hierarchical version of <counter>, which in
513 recent_rotated_anon - VM internal parameter. (see mm/vmscan.c)
514 recent_rotated_file - VM internal parameter. (see mm/vmscan.c)
515 recent_scanned_anon - VM internal parameter. (see mm/vmscan.c)
516 recent_scanned_file - VM internal parameter. (see mm/vmscan.c)
524 Only anonymous and swap cache memory is listed as part of 'rss' stat.
526 amount of physical memory used by the cgroup.
529 mapped_file is accounted only when the memory cgroup is owner of page
544 A memory cgroup provides memory.failcnt and memory.memsw.failcnt files.
546 hit its limit. When a memory cgroup hits a limit, failcnt increases and
547 memory under it will be reclaimed.
550 # echo 0 > .../memory.failcnt
554 For efficiency, as other kernel components, memory cgroup uses some optimization
556 method and doesn't show 'exact' value of memory (and swap) usage, it's a fuzz
558 If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
559 value in memory.stat(see 5.2).
563 This is similar to numa_maps but operates on a per-memcg basis. This is
570 per-node page counts including "hierarchical_<counter>" which sums up all
573 The output format of memory.numa_stat is:
585 The memory controller supports a deep hierarchy and hierarchical accounting.
598 In the diagram above, with hierarchical accounting enabled, all memory
600 that has memory.use_hierarchy enabled. If one of the ancestors goes over its
606 A memory cgroup by default disables the hierarchy feature. Support
607 can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup
609 # echo 1 > memory.use_hierarchy
613 # echo 0 > memory.use_hierarchy
624 Soft limits allow for greater sharing of memory. The idea behind soft limits
625 is to allow control groups to use as much of the memory as needed, provided
627 a. There is no memory contention
630 When the system detects memory contention or low memory, control groups
633 sure that one control group does not starve the others of memory.
635 Please note that soft limits is a best-effort feature; it comes with
636 no guarantees, but it does its best to make sure that when memory is
637 heavily contended for, memory is allocated based on the soft limit
646 # echo 256M > memory.soft_limit_in_bytes
650 # echo 1G > memory.soft_limit_in_bytes
653 reclaiming memory for balancing between memory cgroups
667 writing to memory.move_charge_at_immigrate of the destination cgroup.
671 # echo (some positive value) > memory.move_charge_at_immigrate
675 Note: Charges are moved only when you move mm->owner, in other words,
678 try to make space by reclaiming memory. Task migration may fail if we
684 # echo 0 > memory.move_charge_at_immigrate
691 (old) memory cgroup.
694 -----+------------------------------------------------------------------------
697 -----+------------------------------------------------------------------------
698 1 | A charge of file pages (normal file, tmpfs file (e.g. ipc shared memory)
709 - All of moving charge operations are done under cgroup_mutex. It's not good
712 9. Memory thresholds
714 Memory cgroup implements memory thresholds using the cgroups notification
715 API (see cgroups.txt). It allows to register multiple memory and memsw
719 - create an eventfd using eventfd(2);
720 - open memory.usage_in_bytes or memory.memsw.usage_in_bytes;
721 - write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to
724 Application will be notified through eventfd when memory usage crosses
727 It's applicable for root and non-root cgroup.
731 memory.oom_control file is for OOM notification and other controls.
733 Memory cgroup implements OOM notifier using the cgroup notification
738 - create an eventfd using eventfd(2)
739 - open memory.oom_control file
740 - write string like "<event_fd> <fd of memory.oom_control>" to
746 You can disable the OOM-killer by writing "1" to memory.oom_control file, as:
748 #echo 1 > memory.oom_control
750 If OOM-killer is disabled, tasks under cgroup will hang/sleep
751 in memory cgroup's OOM-waitqueue when they request accountable memory.
753 For running them, you have to relax the memory cgroup's OOM status by
763 oom_kill_disable 0 or 1 (if 1, oom-killer is disabled)
764 under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may
767 11. Memory Pressure
769 The pressure level notifications can be used to monitor the memory
771 different strategies of managing their memory resources. The pressure
774 The "low" level means that the system is reclaiming memory for new
780 The "medium" level means that the system is experiencing medium memory
783 vmstat/zoneinfo/memcg or internal memory usage statistics and free any
784 resources that can be easily reconstructed or re-read from a disk.
787 about to out of memory (OOM) or even the in-kernel OOM killer is on its
793 events are not pass-through. For example, you have three cgroups: A->B->C. Now
798 especially bad if we are low on memory or thrashing. Group B, will receive
803 - "default": this is the default behavior specified above. This mode is the
807 - "hierarchy": events always propagate up to the root, similar to the default
810 example, groups A, B, and C will receive notification of memory pressure.
812 - "local": events are pass-through, i.e. they only receive notifications when
813 memory pressure is experienced in the memcg for which the notification is
815 registered for "local" notification and the group experiences memory
821 specified by a comma-delimited string, i.e. "low,hierarchy" specifies
822 hierarchical, pass-through, notification for all ancestor memcgs. Notification
823 that is the default, non pass-through behavior, does not specify a mode.
824 "medium,local" specifies pass-through notification for the medium level.
826 The file memory.pressure_level is only used to setup an eventfd. To
829 - create an eventfd using eventfd(2);
830 - open memory.pressure_level;
831 - write string as "<event_fd> <fd of memory.pressure_level> <level[,mode]>"
834 Application will be notified through eventfd when memory pressure is at
836 memory.pressure_level are no implemented.
841 memory limit, sets up a notification in the cgroup and then makes child
844 # cd /sys/fs/cgroup/memory/
847 # cgroup_event_listener memory.pressure_level low,hierarchy &
848 # echo 8000000 > memory.limit_in_bytes
849 # echo 8000000 > memory.memsw.limit_in_bytes
853 (Expect a bunch of notifications, and eventually, the oom-killer will
858 1. Make per-cgroup scanner reclaim not-shared pages first
859 2. Teach controller to account for shared-pages
865 Overall, the memory controller has been a stable controller and has been
870 1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
871 2. Singh, Balbir. Memory Controller (RSS Control),
875 4. Emelianov, Pavel. RSS controller based on process cgroups (v2)
877 5. Emelianov, Pavel. RSS controller based on process cgroups (v3)
882 8. Singh, Balbir. RSS controller v2 test results (lmbench),
884 9. Singh, Balbir. RSS controller v2 AIM9 results
886 10. Singh, Balbir. Memory controller v6 test results,
888 11. Singh, Balbir. Memory controller introduction (v6),
890 12. Corbet, Jonathan, Controlling memory use in cgroups,