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Diffstat (limited to 'Documentation/cgroups/memory.txt')
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1 files changed, 306 insertions, 112 deletions
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 7781857dc94..02ab997a1ed 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -1,8 +1,8 @@ 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. +NOTE: The Memory Resource Controller has 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. (For editors) In this document: @@ -18,56 +18,70 @@ from the rest of the system. The article on LWN [12] mentions some probable uses of the memory controller. The memory controller can be used to a. Isolate an application or a group of applications - Memory hungry applications can be isolated and limited to a smaller + Memory-hungry applications can be isolated and limited to a smaller amount of memory. -b. Create a cgroup with limited amount of memory, this can be used +b. Create a cgroup with a limited amount of memory; this can be used as a good alternative to booting with mem=XXXX. c. Virtualization solutions can control the amount of memory they want to assign to a virtual machine instance. d. A CD/DVD burner could control the amount of memory used by the rest of the system to ensure that burning does not fail due to lack of available memory. -e. There are several other use cases, find one or use the controller just +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) + - pages are linked to per-memcg LRU exclusively, and there is no global LRU. - optionally, memory+swap usage can be accounted and limited. - hierarchical accounting - soft limit - - moving(recharging) account at moving a task is selectable. + - 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. - 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. + Kernel memory support is a work in progress, and the current version provides + basically functionality. (See Section 2.7) 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.usage_in_bytes # show current res_counter usage for memory + (See 5.5 for details) + memory.memsw.usage_in_bytes # show current res_counter usage for memory+Swap + (See 5.5 for details) 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.memsw.max_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.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 memory.oom_control # set/show oom controls. + memory.numa_stat # show the number of memory usage per numa node + + memory.kmem.limit_in_bytes # set/show hard limit for kernel memory + memory.kmem.usage_in_bytes # show current kernel memory allocation + memory.kmem.failcnt # show the number of kernel memory usage hits limits + memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded + + memory.kmem.tcp.limit_in_bytes # set/show hard limit for tcp buf memory + memory.kmem.tcp.usage_in_bytes # show current tcp buf memory allocation + memory.kmem.tcp.failcnt # show the number of tcp buf memory usage hits limits + memory.kmem.tcp.max_usage_in_bytes # show max tcp buf memory usage recorded 1. History @@ -137,9 +151,9 @@ Figure 1 shows the important aspects of the controller 3. Each page has a pointer to the page_cgroup, which in turn knows the cgroup it belongs to -The accounting is done as follows: mem_cgroup_charge() is invoked to setup -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. +The accounting is done as follows: mem_cgroup_charge_common() is invoked to +set up 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 updated. page_cgroup has its own LRU on cgroup. @@ -148,7 +162,7 @@ updated. page_cgroup has its own LRU on cgroup. 2.2.1 Accounting details All mapped anon pages (RSS) and cache pages (Page Cache) are accounted. -Some pages which are never reclaimable and will not be on the global LRU +Some pages which are never reclaimable and will not be on the 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 @@ -156,13 +170,13 @@ for earlier. A file page will be accounted for as Page Cache when it's 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 +An RSS page is unaccounted when it's fully unmapped. A PageCache page is 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. +are really freed. Such SwapCaches are 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. +Note: The kernel does swapin-readahead and reads 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. @@ -179,13 +193,15 @@ behind this approach is that a cgroup that aggressively uses a shared page will eventually get charged for it (once it is uncharged from the cgroup that brought it in -- this will happen on memory pressure). -Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.. +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_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. - -2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) +2.4 Swap Extension (CONFIG_MEMCG_SWAP) Swap Extension allows you to record charge for swap. A swapped-in page is charged back to original page allocator if possible. @@ -200,7 +216,7 @@ memsw.limit_in_bytes. 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 +By using the memsw limit, you can avoid system OOM which can be caused by swap shortage. * why 'memory+swap' rather than swap. @@ -208,10 +224,10 @@ 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 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. +an OS point of view. * What happens when a cgroup hits memory.memsw.limit_in_bytes -When a cgroup his memory.memsw.limit_in_bytes, it's useless to do swap-out +When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out in this cgroup. Then, swap-out will not be done by cgroup routine and file caches are dropped. But as mentioned above, global LRU can do swapout memory from it for sanity of the system's memory management state. You can't forbid @@ -227,7 +243,7 @@ an OOM routine is invoked to select and kill the bulkiest task in the 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 +pages that are selected for reclaiming come from the per-cgroup LRU list. NOTE: Reclaim does not work for the root cgroup, since we cannot set any @@ -252,25 +268,106 @@ When oom event notifier is registered, event will be delivered. per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by zone->lru_lock, it has no lock of its own. +2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM) + +WARNING: Current implementation lacks reclaim support. That means allocation + attempts will fail when close to the limit even if there are plenty of + kmem available for reclaim. That makes this option unusable in real + life so DO NOT SELECT IT unless for development purposes. + +With the Kernel memory extension, the Memory Controller is able to limit +the amount of kernel memory used by the system. Kernel memory is fundamentally +different than user memory, since it can't be swapped out, which makes it +possible to DoS the system by consuming too much of this precious resource. + +Kernel memory won't be accounted at all until limit on a group is set. This +allows for existing setups to continue working without disruption. The limit +cannot be set if the cgroup have children, or if there are already tasks in the +cgroup. Attempting to set the limit under those conditions will return -EBUSY. +When use_hierarchy == 1 and a group is accounted, its children will +automatically be accounted regardless of their limit value. + +After a group is first limited, it will be kept being accounted until it +is removed. The memory limitation itself, can of course be removed by writing +-1 to memory.kmem.limit_in_bytes. In this case, kmem will be accounted, but not +limited. + +Kernel memory limits are not imposed for the root cgroup. Usage for the root +cgroup may or may not be accounted. The memory used is accumulated into +memory.kmem.usage_in_bytes, or in a separate counter when it makes sense. +(currently only for tcp). +The main "kmem" counter is fed into the main counter, so kmem charges will +also be visible from the user counter. + +Currently no soft limit is implemented for kernel memory. It is future work +to trigger slab reclaim when those limits are reached. + +2.7.1 Current Kernel Memory resources accounted + +* stack pages: every process consumes some stack pages. By accounting into +kernel memory, we prevent new processes from being created when the kernel +memory usage is too high. + +* slab pages: pages allocated by the SLAB or SLUB allocator are tracked. A copy +of each kmem_cache is created every time the cache is touched by the first time +from inside the memcg. The creation is done lazily, so some objects can still be +skipped while the cache is being created. All objects in a slab page should +belong to the same memcg. This only fails to hold when a task is migrated to a +different memcg during the page allocation by the cache. + +* sockets memory pressure: some sockets protocols have memory pressure +thresholds. The Memory Controller allows them to be controlled individually +per cgroup, instead of globally. + +* tcp memory pressure: sockets memory pressure for the tcp protocol. + +2.7.3 Common use cases + +Because the "kmem" counter is fed to the main user counter, kernel memory can +never be limited completely independently of user memory. Say "U" is the user +limit, and "K" the kernel limit. There are three possible ways limits can be +set: + + U != 0, K = unlimited: + This is the standard memcg limitation mechanism already present before kmem + accounting. Kernel memory is completely ignored. + + U != 0, K < U: + Kernel memory is a subset of the user memory. This setup is useful in + deployments where the total amount of memory per-cgroup is overcommited. + Overcommiting kernel memory limits is definitely not recommended, since the + box can still run out of non-reclaimable memory. + In this case, the admin could set up K so that the sum of all groups is + never greater than the total memory, and freely set U at the cost of his + QoS. + + U != 0, K >= U: + Since kmem charges will also be fed to the user counter and reclaim will be + triggered for the cgroup for both kinds of memory. This setup gives the + admin a unified view of memory, and it is also useful for people who just + want to track kernel memory usage. + 3. User Interface 0. Configuration 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) +c. Enable CONFIG_MEMCG +d. Enable CONFIG_MEMCG_SWAP (to use swap extension) +d. Enable CONFIG_MEMCG_KMEM (to use kmem extension) -1. Prepare the cgroups -# mkdir -p /cgroups -# mount -t cgroup none /cgroups -o memory +1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?) +# mount -t tmpfs none /sys/fs/cgroup +# mkdir /sys/fs/cgroup/memory +# mount -t cgroup none /sys/fs/cgroup/memory -o memory 2. Make the new group and move bash into it -# mkdir /cgroups/0 -# echo $$ > /cgroups/0/tasks +# mkdir /sys/fs/cgroup/memory/0 +# echo $$ > /sys/fs/cgroup/memory/0/tasks Since now we're in the 0 cgroup, we can alter the memory limit: -# echo 4M > /cgroups/0/memory.limit_in_bytes +# echo 4M > /sys/fs/cgroup/memory/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. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes, Gibibytes.) @@ -278,14 +375,14 @@ 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 +# cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes 4194304 We can check the usage: -# cat /cgroups/0/memory.usage_in_bytes +# cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes 1216512 -A successful write to this file does not guarantee a successful set of +A successful write to this file does not guarantee a successful setting of 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 @@ -319,7 +416,7 @@ 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 by OOM killer. There are several causes for this: +terminated by the 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 @@ -327,7 +424,7 @@ terminated by OOM killer. 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 +To know what happens, disabling OOM_Kill as per "10. OOM Control" (below) and seeing what happens will be helpful. 4.2 Task migration @@ -347,48 +444,59 @@ cgroup might have some charge associated with it, even though all 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. +We move the stats to root (if use_hierarchy==0) or parent (if +use_hierarchy==1), and no change on the charge except uncharging +from the child. Charges recorded in swap information is not updated at removal of cgroup. Recorded information is discarded and a cgroup which uses swap (swapcache) will be charged as a new owner of it. +About use_hierarchy, see Section 6. 5. Misc. interfaces. 5.1 force_empty memory.force_empty interface is provided to make cgroup's memory usage empty. - You can use this interface only when the cgroup has no tasks. When writing anything to this # echo 0 > memory.force_empty - 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. + the cgroup will be reclaimed and as many pages reclaimed as possible. - Typical use case of this interface is that calling this before rmdir(). + The typical use case for this interface is before calling rmdir(). Because rmdir() moves all pages to parent, some out-of-use page caches can be moved to the parent. If you want to avoid that, force_empty will be useful. + Also, note that when memory.kmem.limit_in_bytes is set the charges due to + kernel pages will still be seen. This is not considered a failure and the + write will still return success. In this case, it is expected that + memory.kmem.usage_in_bytes == memory.usage_in_bytes. + + About use_hierarchy, see Section 6. + 5.2 stat file 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. +rss - # of bytes of anonymous and swap cache memory (includes + transparent hugepages). +rss_huge - # of bytes of anonymous transparent hugepages. 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). +pgpgin - # of charging events to the memory cgroup. The charging + event happens each time a page is accounted as either mapped + anon page(RSS) or cache page(Page Cache) to the cgroup. +pgpgout - # of uncharging events to the memory cgroup. The uncharging + event happens each time a page is unaccounted from the cgroup. swap - # of bytes of swap usage -inactive_anon - # of bytes of anonymous memory and swap cache memory on +writeback - # of bytes of file/anon cache that are queued for syncing to + disk. +inactive_anon - # of bytes of anonymous and swap cache memory on inactive LRU list. active_anon - # of bytes of anonymous and swap cache memory on active - inactive LRU list. + 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). @@ -400,21 +508,13 @@ hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy 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" +total_<counter> - # hierarchical version of <counter>, which in + addition to the cgroup's own value includes the + sum of all hierarchical children's values of + <counter>, i.e. total_cache # 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) recent_rotated_file - VM internal parameter. (see mm/vmscan.c) recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) @@ -436,12 +536,13 @@ Note: 5.3 swappiness -Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. +Overrides /proc/sys/vm/swappiness for the particular group. The tunable +in the root cgroup corresponds to the global swappiness setting. -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. +Please note that unlike during the global reclaim, limit reclaim +enforces that 0 swappiness really prevents from any swapping even if +there is a swap storage available. This might lead to memcg OOM killer +if there are no file pages to reclaim. 5.4 failcnt @@ -453,6 +554,37 @@ memory under it will be reclaimed. You can reset failcnt by writing 0 to failcnt file. # echo 0 > .../memory.failcnt +5.5 usage_in_bytes + +For efficiency, as other kernel components, memory cgroup uses some optimization +to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the +method and doesn't show 'exact' value of memory (and swap) usage, it's a fuzz +value for efficient access. (Of course, when necessary, it's synchronized.) +If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP) +value in memory.stat(see 5.2). + +5.6 numa_stat + +This is similar to numa_maps but operates on a per-memcg basis. This is +useful for providing visibility into the numa locality information within +an memcg since the pages are allowed to be allocated from any physical +node. One of the use cases is evaluating application performance by +combining this information with the application's CPU allocation. + +Each memcg's numa_stat file includes "total", "file", "anon" and "unevictable" +per-node page counts including "hierarchical_<counter>" which sums up all +hierarchical children's values in addition to the memcg's own value. + +The output format of memory.numa_stat is: + +total=<total pages> N0=<node 0 pages> N1=<node 1 pages> ... +file=<total file pages> N0=<node 0 pages> N1=<node 1 pages> ... +anon=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ... +unevictable=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ... +hierarchical_<counter>=<counter pages> N0=<node 0 pages> N1=<node 1 pages> ... + +The "total" count is sum of file + anon + unevictable. + 6. Hierarchy support The memory controller supports a deep hierarchy and hierarchical accounting. @@ -460,13 +592,13 @@ The hierarchy is created by creating the appropriate cgroups in the cgroup filesystem. Consider for example, the following cgroup filesystem hierarchy - root + root / | \ - / | \ - a b c - | \ - | \ - d e + / | \ + a b c + | \ + | \ + d e 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), @@ -485,8 +617,9 @@ 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. +NOTE1: Enabling/disabling will fail if either the cgroup already has other + cgroups created below it, or if the parent cgroup has use_hierarchy + enabled. NOTE2: When panic_on_oom is set to "2", the whole system will panic in case of an OOM event in any cgroup. @@ -504,10 +637,10 @@ 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. -Please note that soft limits is a best effort feature, it comes with +Please note that soft limits is a best-effort feature; it comes with no guarantees, but it does its best to make sure that when memory is heavily contended for, memory is allocated based on the soft limit -hints/setup. Currently soft limit based reclaim is setup such that +hints/setup. Currently soft limit based reclaim is set up such that it gets invoked from balance_pgdat (kswapd). 7.1 Interface @@ -535,7 +668,7 @@ page tables. 8.1 Interface -This feature is disabled by default. It can be enabled(and disabled again) by +This feature is disabled by default. It can be enabled (and disabled again) by writing to memory.move_charge_at_immigrate of the destination cgroup. If you want to enable it: @@ -544,8 +677,8 @@ If you want to enable it: Note: Each bits of move_charge_at_immigrate has its own meaning about what type of charges should be moved. See 8.2 for details. -Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread - group. +Note: Charges are moved only when you move mm->owner, in other words, + a leader of a thread group. 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. @@ -555,42 +688,39 @@ And if you want disable it again: # echo 0 > memory.move_charge_at_immigrate -8.2 Type of charges which can be move +8.2 Type of charges which can be moved -Each bits of move_charge_at_immigrate has its own meaning about what type of -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. +Each bit in move_charge_at_immigrate has its own meaning about what type of +charges should be moved. But in any case, 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. + 0 | A charge of an anonymous page (or swap of it) used by the target task. + | You must enable Swap Extension (see 2.4) to enable move of swap charges. -----+------------------------------------------------------------------------ - 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) + 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 + | 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 + | 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 -- 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 behavior to hold the mutex too long, so we may need some trick. 9. Memory thresholds -Memory cgroup implements memory thresholds using cgroups notification +Memory cgroup implements memory thresholds using the 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: +To register a threshold, an application must: - 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 @@ -605,24 +735,23 @@ It's applicable for root and non-root cgroup. memory.oom_control file is for OOM notification and other controls. -Memory cgroup implements OOM notifier using cgroup notification +Memory cgroup implements OOM notifier using the 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: +To register a notifier, an application must: - 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. +The application will be notified through eventfd when OOM happens. +OOM notification doesn't work for the root cgroup. -You can disable OOM-killer by writing "1" to memory.oom_control file, as: +You can disable the 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. @@ -640,12 +769,77 @@ 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 -3. Teach controller to account for shared-pages -4. Start reclamation in the background when the limit is +1. Make per-cgroup scanner reclaim not-shared pages first +2. Teach controller to account for shared-pages +3. Start reclamation in the background when the limit is not yet hit but the usage is getting closer Summary |