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
80 memory.force_empty trigger forced page reclaim
81 memory.pressure_level set memory pressure notifications
82 memory.swappiness set/show swappiness parameter of vmscan
84 memory.move_charge_at_immigrate set/show controls of moving charges
85 memory.oom_control set/show oom controls.
86 memory.numa_stat show the number of memory usage per numa
88 memory.kmem.limit_in_bytes set/show hard limit for kernel memory
92 memory.kmem.usage_in_bytes show current kernel memory allocation
93 memory.kmem.failcnt show the number of kernel memory usage
95 memory.kmem.max_usage_in_bytes show max kernel memory usage recorded
97 memory.kmem.tcp.limit_in_bytes set/show hard limit for tcp buf memory
98 memory.kmem.tcp.usage_in_bytes show current tcp buf memory allocation
99 memory.kmem.tcp.failcnt show the number of tcp buf memory usage
101 memory.kmem.tcp.max_usage_in_bytes show max tcp buf memory usage recorded
107 The memory controller has a long history. A request for comments for the memory
109 there were several implementations for memory control. The goal of the
111 for memory control. The first RSS controller was posted by Balbir Singh[2]
115 to allow user space handling of OOM. The current memory controller is
119 2. Memory Control
122 Memory is a unique resource in the sense that it is present in a limited
125 memory, the same physical memory needs to be reused to accomplish the task.
127 The memory controller implementation has been divided into phases. These
130 1. Memory controller
132 3. Kernel user memory accounting and slab control
135 The memory controller is the first controller developed.
141 page_counter tracks the current memory usage and limit of the group of
142 processes associated with the controller. Each cgroup has a memory controller
184 (*) page_cgroup structure is allocated at boot/memory-hotplug time.
220 the cgroup that brought it in -- this will happen on memory pressure).
233 - memory.memsw.usage_in_bytes.
234 - memory.memsw.limit_in_bytes.
236 memsw means memory+swap. Usage of memory+swap is limited by
239 Example: Assume a system with 4G of swap. A task which allocates 6G of memory
240 (by mistake) under 2G memory limitation will use all swap.
245 **why 'memory+swap' rather than swap**
248 to move account from memory to swap...there is no change in usage of
249 memory+swap. In other words, when we want to limit the usage of swap without
250 affecting global LRU, memory+swap limit is better than just limiting swap from
253 **What happens when a cgroup hits memory.memsw.limit_in_bytes**
255 When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
257 caches are dropped. But as mentioned above, global LRU can do swapout memory
258 from it for sanity of the system's memory management state. You can't forbid
266 to reclaim memory from the cgroup so as to make space for the new
303 2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
306 With the Kernel memory extension, the Memory Controller is able to limit
307 the amount of kernel memory used by the system. Kernel memory is fundamentally
308 different than user memory, since it can't be swapped out, which makes it
311 Kernel memory accounting is enabled for all memory cgroups by default. But
312 it can be disabled system-wide by passing cgroup.memory=nokmem to the kernel
313 at boot time. In this case, kernel memory will not be accounted at all.
315 Kernel memory limits are not imposed for the root cgroup. Usage for the root
316 cgroup may or may not be accounted. The memory used is accumulated into
317 memory.kmem.usage_in_bytes, or in a separate counter when it makes sense.
323 Currently no soft limit is implemented for kernel memory. It is future work
326 2.7.1 Current Kernel Memory resources accounted
331 kernel memory, we prevent new processes from being created when the kernel
332 memory usage is too high.
342 sockets memory pressure:
343 some sockets protocols have memory pressure
344 thresholds. The Memory Controller allows them to be controlled individually
347 tcp memory pressure:
348 sockets memory pressure for the tcp protocol.
353 Because the "kmem" counter is fed to the main user counter, kernel memory can
354 never be limited completely independently of user memory. Say "U" is the user
360 accounting. Kernel memory is completely ignored.
363 Kernel memory is a subset of the user memory. This setup is useful in
364 deployments where the total amount of memory per-cgroup is overcommited.
365 Overcommiting kernel memory limits is definitely not recommended, since the
366 box can still run out of non-reclaimable memory.
368 never greater than the total memory, and freely set U at the cost of his
372 In the current implementation, memory reclaim will NOT be
378 triggered for the cgroup for both kinds of memory. This setup gives the
379 admin a unified view of memory, and it is also useful for people who just
380 want to track kernel memory usage.
399 # mkdir /sys/fs/cgroup/memory
400 # mount -t cgroup none /sys/fs/cgroup/memory -o memory
404 # mkdir /sys/fs/cgroup/memory/0
405 # echo $$ > /sys/fs/cgroup/memory/0/tasks
407 Since now we're in the 0 cgroup, we can alter the memory limit::
409 # echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes
424 # cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
429 # cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
435 availability of memory on the system. The user is required to re-read
438 # echo 1 > memory.limit_in_bytes
439 # cat memory.limit_in_bytes
442 The memory.failcnt field gives the number of times that the cgroup limit was
445 The memory.stat file gives accounting information. Now, the number of
453 Performance test is also important. To see pure memory controller's overhead,
462 Trying usual test under memory controller is always helpful.
471 2. The user is using anonymous memory and swap is turned off or too low
513 memory.force_empty interface is provided to make cgroup's memory usage empty.
516 # echo 0 > memory.force_empty
523 memory pressure happens. If you want to avoid that, force_empty will be useful.
525 Also, note that when memory.kmem.limit_in_bytes is set the charges due to
528 memory.kmem.usage_in_bytes == memory.usage_in_bytes.
535 memory.stat file includes following statistics
537 per-memory cgroup local status
541 cache # of bytes of page cache memory.
542 rss # of bytes of anonymous and swap cache memory (includes
546 pgpgin # of charging events to the memory cgroup. The charging
549 pgpgout # of uncharging events to the memory cgroup. The uncharging
555 inactive_anon # of bytes of anonymous and swap cache memory on inactive
557 active_anon # of bytes of anonymous and swap cache memory on active
559 inactive_file # of bytes of file-backed memory on inactive LRU list.
560 active_file # of bytes of file-backed memory on active LRU list.
561 unevictable # of bytes of memory that cannot be reclaimed (mlocked etc).
564 status considering hierarchy (see memory.use_hierarchy settings)
568 hierarchical_memory_limit # of bytes of memory limit with regard to hierarchy
569 under which the memory cgroup is
570 hierarchical_memsw_limit # of bytes of memory+swap limit with regard to
571 hierarchy under which memory cgroup is.
595 Only anonymous and swap cache memory is listed as part of 'rss' stat.
597 amount of physical memory used by the cgroup.
602 mapped_file is accounted only when the memory cgroup is owner of page
619 A memory cgroup provides memory.failcnt and memory.memsw.failcnt files.
621 hit its limit. When a memory cgroup hits a limit, failcnt increases and
622 memory under it will be reclaimed.
626 # echo 0 > .../memory.failcnt
631 For efficiency, as other kernel components, memory cgroup uses some optimization
633 method and doesn't show 'exact' value of memory (and swap) usage, it's a fuzz
635 If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
636 value in memory.stat(see 5.2).
651 The output format of memory.numa_stat is::
664 The memory controller supports a deep hierarchy and hierarchical accounting.
677 In the diagram above, with hierarchical accounting enabled, all memory
679 that has memory.use_hierarchy enabled. If one of the ancestors goes over its
686 A memory cgroup by default disables the hierarchy feature. Support
687 can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup::
689 # echo 1 > memory.use_hierarchy
693 # echo 0 > memory.use_hierarchy
707 Soft limits allow for greater sharing of memory. The idea behind soft limits
708 is to allow control groups to use as much of the memory as needed, provided
710 a. There is no memory contention
713 When the system detects memory contention or low memory, control groups
716 sure that one control group does not starve the others of memory.
719 no guarantees, but it does its best to make sure that when memory is
720 heavily contended for, memory is allocated based on the soft limit
730 # echo 256M > memory.soft_limit_in_bytes
734 # echo 1G > memory.soft_limit_in_bytes
738 reclaiming memory for balancing between memory cgroups
755 writing to memory.move_charge_at_immigrate of the destination cgroup.
759 # echo (some positive value) > memory.move_charge_at_immigrate
769 try to make space by reclaiming memory. Task migration may fail if we
776 # echo 0 > memory.move_charge_at_immigrate
784 (old) memory cgroup.
792 | 1 | A charge of file pages (normal file, tmpfs file (e.g. ipc shared memory) |
808 9. Memory thresholds
811 Memory cgroup implements memory thresholds using the cgroups notification
812 API (see cgroups.txt). It allows to register multiple memory and memsw
818 - open memory.usage_in_bytes or memory.memsw.usage_in_bytes;
819 - write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to
822 Application will be notified through eventfd when memory usage crosses
830 memory.oom_control file is for OOM notification and other controls.
832 Memory cgroup implements OOM notifier using the cgroup notification
839 - open memory.oom_control file
840 - write string like "<event_fd> <fd of memory.oom_control>" to
846 You can disable the OOM-killer by writing "1" to memory.oom_control file, as:
848 #echo 1 > memory.oom_control
851 in memory cgroup's OOM-waitqueue when they request accountable memory.
853 For running them, you have to relax the memory cgroup's OOM status by
870 (if 1, the memory cgroup is under OOM, tasks may be stopped.)
872 11. Memory Pressure
875 The pressure level notifications can be used to monitor the memory
877 different strategies of managing their memory resources. The pressure
880 The "low" level means that the system is reclaiming memory for new
886 The "medium" level means that the system is experiencing medium memory
889 vmstat/zoneinfo/memcg or internal memory usage statistics and free any
893 about to out of memory (OOM) or even the in-kernel OOM killer is on its
904 especially bad if we are low on memory or thrashing. Group B, will receive
916 example, groups A, B, and C will receive notification of memory pressure.
919 memory pressure is experienced in the memcg for which the notification is
921 registered for "local" notification and the group experiences memory
932 The file memory.pressure_level is only used to setup an eventfd. To
936 - open memory.pressure_level;
937 - write string as "<event_fd> <fd of memory.pressure_level> <level[,mode]>"
940 Application will be notified through eventfd when memory pressure is at
942 memory.pressure_level are no implemented.
947 memory limit, sets up a notification in the cgroup and then makes child
950 # cd /sys/fs/cgroup/memory/
953 # cgroup_event_listener memory.pressure_level low,hierarchy &
954 # echo 8000000 > memory.limit_in_bytes
955 # echo 8000000 > memory.memsw.limit_in_bytes
973 Overall, the memory controller has been a stable controller and has been
979 1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
980 2. Singh, Balbir. Memory Controller (RSS Control),
995 10. Singh, Balbir. Memory controller v6 test results,
997 11. Singh, Balbir. Memory controller introduction (v6),
999 12. Corbet, Jonathan, Controlling memory use in cgroups,