Lines Matching full:memory
2 Memory Resource Controller
12 The Memory Resource Controller has generically been referred to as the
13 memory controller in this document. Do not confuse memory controller
14 used here with the memory controller that is used in hardware.
17 When we mention a cgroup (cgroupfs's directory) with memory controller,
18 we call it "memory cgroup". When you see git-log and source code, you'll
22 Benefits and Purpose of the memory controller
25 The memory controller isolates the memory behaviour of a group of tasks
27 uses of the memory controller. The memory controller can be used to
30 Memory-hungry applications can be isolated and limited to a smaller
31 amount of memory.
32 b. Create a cgroup with a limited amount of memory; this can be used
34 c. Virtualization solutions can control the amount of memory they want
36 d. A CD/DVD burner could control the amount of memory used by the
38 of available memory.
48 - optionally, memory+swap usage can be accounted and limited.
53 - memory pressure notifier
57 Kernel memory support is a work in progress, and the current version provides
67 memory.usage_in_bytes show current usage for memory
69 memory.memsw.usage_in_bytes show current usage for memory+Swap
71 memory.limit_in_bytes set/show limit of memory usage
72 memory.memsw.limit_in_bytes set/show limit of memory+Swap usage
73 memory.failcnt show the number of memory usage hits limits
74 memory.memsw.failcnt show the number of memory+Swap hits limits
75 memory.max_usage_in_bytes show max memory usage recorded
76 memory.memsw.max_usage_in_bytes show max memory+Swap usage recorded
77 memory.soft_limit_in_bytes set/show soft limit of memory usage
78 memory.stat show various statistics
79 memory.use_hierarchy set/show hierarchical account enabled
82 memory.force_empty trigger forced page reclaim
83 memory.pressure_level set memory pressure notifications
84 memory.swappiness set/show swappiness parameter of vmscan
86 memory.move_charge_at_immigrate set/show controls of moving charges
87 memory.oom_control set/show oom controls.
88 memory.numa_stat show the number of memory usage per numa
90 memory.kmem.limit_in_bytes set/show hard limit for kernel memory
94 memory.kmem.usage_in_bytes show current kernel memory allocation
95 memory.kmem.failcnt show the number of kernel memory usage
97 memory.kmem.max_usage_in_bytes show max kernel memory usage recorded
99 memory.kmem.tcp.limit_in_bytes set/show hard limit for tcp buf memory
100 memory.kmem.tcp.usage_in_bytes show current tcp buf memory allocation
101 memory.kmem.tcp.failcnt show the number of tcp buf memory usage
103 memory.kmem.tcp.max_usage_in_bytes show max tcp buf memory usage recorded
109 The memory controller has a long history. A request for comments for the memory
111 there were several implementations for memory control. The goal of the
113 for memory control. The first RSS controller was posted by Balbir Singh[2]
117 to allow user space handling of OOM. The current memory controller is
121 2. Memory Control
124 Memory is a unique resource in the sense that it is present in a limited
127 memory, the same physical memory needs to be reused to accomplish the task.
129 The memory controller implementation has been divided into phases. These
132 1. Memory controller
134 3. Kernel user memory accounting and slab control
137 The memory controller is the first controller developed.
143 page_counter tracks the current memory usage and limit of the group of
144 processes associated with the controller. Each cgroup has a memory controller
186 (*) page_cgroup structure is allocated at boot/memory-hotplug time.
222 the cgroup that brought it in -- this will happen on memory pressure).
235 - memory.memsw.usage_in_bytes.
236 - memory.memsw.limit_in_bytes.
238 memsw means memory+swap. Usage of memory+swap is limited by
241 Example: Assume a system with 4G of swap. A task which allocates 6G of memory
242 (by mistake) under 2G memory limitation will use all swap.
247 **why 'memory+swap' rather than swap**
250 to move account from memory to swap...there is no change in usage of
251 memory+swap. In other words, when we want to limit the usage of swap without
252 affecting global LRU, memory+swap limit is better than just limiting swap from
255 **What happens when a cgroup hits memory.memsw.limit_in_bytes**
257 When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
259 caches are dropped. But as mentioned above, global LRU can do swapout memory
260 from it for sanity of the system's memory management state. You can't forbid
268 to reclaim memory from the cgroup so as to make space for the new
302 2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
305 With the Kernel memory extension, the Memory Controller is able to limit
306 the amount of kernel memory used by the system. Kernel memory is fundamentally
307 different than user memory, since it can't be swapped out, which makes it
310 Kernel memory accounting is enabled for all memory cgroups by default. But
311 it can be disabled system-wide by passing cgroup.memory=nokmem to the kernel
312 at boot time. In this case, kernel memory will not be accounted at all.
314 Kernel memory limits are not imposed for the root cgroup. Usage for the root
315 cgroup may or may not be accounted. The memory used is accumulated into
316 memory.kmem.usage_in_bytes, or in a separate counter when it makes sense.
322 Currently no soft limit is implemented for kernel memory. It is future work
325 2.7.1 Current Kernel Memory resources accounted
330 kernel memory, we prevent new processes from being created when the kernel
331 memory usage is too high.
341 sockets memory pressure:
342 some sockets protocols have memory pressure
343 thresholds. The Memory Controller allows them to be controlled individually
346 tcp memory pressure:
347 sockets memory pressure for the tcp protocol.
352 Because the "kmem" counter is fed to the main user counter, kernel memory can
353 never be limited completely independently of user memory. Say "U" is the user
359 accounting. Kernel memory is completely ignored.
362 Kernel memory is a subset of the user memory. This setup is useful in
363 deployments where the total amount of memory per-cgroup is overcommitted.
364 Overcommitting kernel memory limits is definitely not recommended, since the
365 box can still run out of non-reclaimable memory.
367 never greater than the total memory, and freely set U at the cost of his
371 In the current implementation, memory reclaim will NOT be
377 triggered for the cgroup for both kinds of memory. This setup gives the
378 admin a unified view of memory, and it is also useful for people who just
379 want to track kernel memory usage.
398 # mkdir /sys/fs/cgroup/memory
399 # mount -t cgroup none /sys/fs/cgroup/memory -o memory
403 # mkdir /sys/fs/cgroup/memory/0
404 # echo $$ > /sys/fs/cgroup/memory/0/tasks
406 Since now we're in the 0 cgroup, we can alter the memory limit::
408 # echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes
423 # cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
428 # cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
434 availability of memory on the system. The user is required to re-read
437 # echo 1 > memory.limit_in_bytes
438 # cat memory.limit_in_bytes
441 The memory.failcnt field gives the number of times that the cgroup limit was
444 The memory.stat file gives accounting information. Now, the number of
452 Performance test is also important. To see pure memory controller's overhead,
461 Trying usual test under memory controller is always helpful.
470 2. The user is using anonymous memory and swap is turned off or too low
509 memory.force_empty interface is provided to make cgroup's memory usage empty.
512 # echo 0 > memory.force_empty
519 memory pressure happens. If you want to avoid that, force_empty will be useful.
521 Also, note that when memory.kmem.limit_in_bytes is set the charges due to
524 memory.kmem.usage_in_bytes == memory.usage_in_bytes.
529 memory.stat file includes following statistics
531 per-memory cgroup local status
535 cache # of bytes of page cache memory.
536 rss # of bytes of anonymous and swap cache memory (includes
540 pgpgin # of charging events to the memory cgroup. The charging
543 pgpgout # of uncharging events to the memory cgroup. The uncharging
549 inactive_anon # of bytes of anonymous and swap cache memory on inactive
551 active_anon # of bytes of anonymous and swap cache memory on active
553 inactive_file # of bytes of file-backed memory on inactive LRU list.
554 active_file # of bytes of file-backed memory on active LRU list.
555 unevictable # of bytes of memory that cannot be reclaimed (mlocked etc).
558 status considering hierarchy (see memory.use_hierarchy settings)
562 hierarchical_memory_limit # of bytes of memory limit with regard to hierarchy
563 under which the memory cgroup is
564 hierarchical_memsw_limit # of bytes of memory+swap limit with regard to
565 hierarchy under which memory cgroup is.
589 Only anonymous and swap cache memory is listed as part of 'rss' stat.
591 amount of physical memory used by the cgroup.
596 mapped_file is accounted only when the memory cgroup is owner of page
613 A memory cgroup provides memory.failcnt and memory.memsw.failcnt files.
615 hit its limit. When a memory cgroup hits a limit, failcnt increases and
616 memory under it will be reclaimed.
620 # echo 0 > .../memory.failcnt
625 For efficiency, as other kernel components, memory cgroup uses some optimization
627 method and doesn't show 'exact' value of memory (and swap) usage, it's a fuzz
629 If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
630 value in memory.stat(see 5.2).
645 The output format of memory.numa_stat is::
658 The memory controller supports a deep hierarchy and hierarchical accounting.
671 In the diagram above, with hierarchical accounting enabled, all memory
683 For compatibility reasons writing 1 to memory.use_hierarchy will always pass::
685 # echo 1 > memory.use_hierarchy
690 Soft limits allow for greater sharing of memory. The idea behind soft limits
691 is to allow control groups to use as much of the memory as needed, provided
693 a. There is no memory contention
696 When the system detects memory contention or low memory, control groups
699 sure that one control group does not starve the others of memory.
702 no guarantees, but it does its best to make sure that when memory is
703 heavily contended for, memory is allocated based on the soft limit
713 # echo 256M > memory.soft_limit_in_bytes
717 # echo 1G > memory.soft_limit_in_bytes
721 reclaiming memory for balancing between memory cgroups
738 writing to memory.move_charge_at_immigrate of the destination cgroup.
742 # echo (some positive value) > memory.move_charge_at_immigrate
752 try to make space by reclaiming memory. Task migration may fail if we
759 # echo 0 > memory.move_charge_at_immigrate
767 (old) memory cgroup.
775 | 1 | A charge of file pages (normal file, tmpfs file (e.g. ipc shared memory) |
791 9. Memory thresholds
794 Memory cgroup implements memory thresholds using the cgroups notification
795 API (see cgroups.txt). It allows to register multiple memory and memsw
801 - open memory.usage_in_bytes or memory.memsw.usage_in_bytes;
802 - write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to
805 Application will be notified through eventfd when memory usage crosses
813 memory.oom_control file is for OOM notification and other controls.
815 Memory cgroup implements OOM notifier using the cgroup notification
822 - open memory.oom_control file
823 - write string like "<event_fd> <fd of memory.oom_control>" to
829 You can disable the OOM-killer by writing "1" to memory.oom_control file, as:
831 #echo 1 > memory.oom_control
834 in memory cgroup's OOM-waitqueue when they request accountable memory.
836 For running them, you have to relax the memory cgroup's OOM status by
853 (if 1, the memory cgroup is under OOM, tasks may be stopped.)
858 11. Memory Pressure
861 The pressure level notifications can be used to monitor the memory
863 different strategies of managing their memory resources. The pressure
866 The "low" level means that the system is reclaiming memory for new
872 The "medium" level means that the system is experiencing medium memory
875 vmstat/zoneinfo/memcg or internal memory usage statistics and free any
879 about to out of memory (OOM) or even the in-kernel OOM killer is on its
890 especially bad if we are low on memory or thrashing. Group B, will receive
902 example, groups A, B, and C will receive notification of memory pressure.
905 memory pressure is experienced in the memcg for which the notification is
907 registered for "local" notification and the group experiences memory
918 The file memory.pressure_level is only used to setup an eventfd. To
922 - open memory.pressure_level;
923 - write string as "<event_fd> <fd of memory.pressure_level> <level[,mode]>"
926 Application will be notified through eventfd when memory pressure is at
928 memory.pressure_level are no implemented.
933 memory limit, sets up a notification in the cgroup and then makes child
936 # cd /sys/fs/cgroup/memory/
939 # cgroup_event_listener memory.pressure_level low,hierarchy &
940 # echo 8000000 > memory.limit_in_bytes
941 # echo 8000000 > memory.memsw.limit_in_bytes
959 Overall, the memory controller has been a stable controller and has been
965 1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
966 2. Singh, Balbir. Memory Controller (RSS Control),
981 10. Singh, Balbir. Memory controller v6 test results,
983 11. Singh, Balbir. Memory controller introduction (v6),
985 12. Corbet, Jonathan, Controlling memory use in cgroups,