Balbir Singh | 00f0b82 | 2008-03-04 14:28:39 -0800 | [diff] [blame] | 1 | Memory Resource Controller |
| 2 | |
| 3 | NOTE: The Memory Resource Controller has been generically been referred |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 4 | to as the memory controller in this document. Do not confuse memory |
| 5 | controller used here with the memory controller that is used in hardware. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 6 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 7 | (For editors) |
| 8 | In this document: |
| 9 | When we mention a cgroup (cgroupfs's directory) with memory controller, |
| 10 | we call it "memory cgroup". When you see git-log and source code, you'll |
| 11 | see patch's title and function names tend to use "memcg". |
| 12 | In this document, we avoid using it. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 13 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 14 | Benefits and Purpose of the memory controller |
| 15 | |
| 16 | The memory controller isolates the memory behaviour of a group of tasks |
| 17 | from the rest of the system. The article on LWN [12] mentions some probable |
| 18 | uses of the memory controller. The memory controller can be used to |
| 19 | |
| 20 | a. Isolate an application or a group of applications |
| 21 | Memory hungry applications can be isolated and limited to a smaller |
| 22 | amount of memory. |
| 23 | b. Create a cgroup with limited amount of memory, this can be used |
| 24 | as a good alternative to booting with mem=XXXX. |
| 25 | c. Virtualization solutions can control the amount of memory they want |
| 26 | to assign to a virtual machine instance. |
| 27 | d. A CD/DVD burner could control the amount of memory used by the |
| 28 | rest of the system to ensure that burning does not fail due to lack |
| 29 | of available memory. |
| 30 | e. There are several other use cases, find one or use the controller just |
| 31 | for fun (to learn and hack on the VM subsystem). |
| 32 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 33 | Current Status: linux-2.6.34-mmotm(development version of 2010/April) |
| 34 | |
| 35 | Features: |
| 36 | - accounting anonymous pages, file caches, swap caches usage and limiting them. |
| 37 | - private LRU and reclaim routine. (system's global LRU and private LRU |
| 38 | work independently from each other) |
| 39 | - optionally, memory+swap usage can be accounted and limited. |
| 40 | - hierarchical accounting |
| 41 | - soft limit |
| 42 | - moving(recharging) account at moving a task is selectable. |
| 43 | - usage threshold notifier |
| 44 | - oom-killer disable knob and oom-notifier |
| 45 | - Root cgroup has no limit controls. |
| 46 | |
| 47 | Kernel memory and Hugepages are not under control yet. We just manage |
| 48 | pages on LRU. To add more controls, we have to take care of performance. |
| 49 | |
| 50 | Brief summary of control files. |
| 51 | |
| 52 | tasks # attach a task(thread) and show list of threads |
| 53 | cgroup.procs # show list of processes |
| 54 | cgroup.event_control # an interface for event_fd() |
Daisuke Nishimura | a111c96 | 2011-04-27 15:26:48 -0700 | [diff] [blame] | 55 | memory.usage_in_bytes # show current res_counter usage for memory |
| 56 | (See 5.5 for details) |
| 57 | memory.memsw.usage_in_bytes # show current res_counter usage for memory+Swap |
| 58 | (See 5.5 for details) |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 59 | memory.limit_in_bytes # set/show limit of memory usage |
| 60 | memory.memsw.limit_in_bytes # set/show limit of memory+Swap usage |
| 61 | memory.failcnt # show the number of memory usage hits limits |
| 62 | memory.memsw.failcnt # show the number of memory+Swap hits limits |
| 63 | memory.max_usage_in_bytes # show max memory usage recorded |
| 64 | memory.memsw.usage_in_bytes # show max memory+Swap usage recorded |
| 65 | memory.soft_limit_in_bytes # set/show soft limit of memory usage |
| 66 | memory.stat # show various statistics |
| 67 | memory.use_hierarchy # set/show hierarchical account enabled |
| 68 | memory.force_empty # trigger forced move charge to parent |
| 69 | memory.swappiness # set/show swappiness parameter of vmscan |
| 70 | (See sysctl's vm.swappiness) |
| 71 | memory.move_charge_at_immigrate # set/show controls of moving charges |
| 72 | memory.oom_control # set/show oom controls. |
Ying Han | 50c35e5 | 2011-06-15 15:08:16 -0700 | [diff] [blame] | 73 | memory.numa_stat # show the number of memory usage per numa node |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 74 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 75 | 1. History |
| 76 | |
| 77 | The memory controller has a long history. A request for comments for the memory |
| 78 | controller was posted by Balbir Singh [1]. At the time the RFC was posted |
| 79 | there were several implementations for memory control. The goal of the |
| 80 | RFC was to build consensus and agreement for the minimal features required |
| 81 | for memory control. The first RSS controller was posted by Balbir Singh[2] |
| 82 | in Feb 2007. Pavel Emelianov [3][4][5] has since posted three versions of the |
| 83 | RSS controller. At OLS, at the resource management BoF, everyone suggested |
| 84 | that we handle both page cache and RSS together. Another request was raised |
| 85 | to allow user space handling of OOM. The current memory controller is |
| 86 | at version 6; it combines both mapped (RSS) and unmapped Page |
| 87 | Cache Control [11]. |
| 88 | |
| 89 | 2. Memory Control |
| 90 | |
| 91 | Memory is a unique resource in the sense that it is present in a limited |
| 92 | amount. If a task requires a lot of CPU processing, the task can spread |
| 93 | its processing over a period of hours, days, months or years, but with |
| 94 | memory, the same physical memory needs to be reused to accomplish the task. |
| 95 | |
| 96 | The memory controller implementation has been divided into phases. These |
| 97 | are: |
| 98 | |
| 99 | 1. Memory controller |
| 100 | 2. mlock(2) controller |
| 101 | 3. Kernel user memory accounting and slab control |
| 102 | 4. user mappings length controller |
| 103 | |
| 104 | The memory controller is the first controller developed. |
| 105 | |
| 106 | 2.1. Design |
| 107 | |
| 108 | The core of the design is a counter called the res_counter. The res_counter |
| 109 | tracks the current memory usage and limit of the group of processes associated |
| 110 | with the controller. Each cgroup has a memory controller specific data |
| 111 | structure (mem_cgroup) associated with it. |
| 112 | |
| 113 | 2.2. Accounting |
| 114 | |
| 115 | +--------------------+ |
| 116 | | mem_cgroup | |
| 117 | | (res_counter) | |
| 118 | +--------------------+ |
| 119 | / ^ \ |
| 120 | / | \ |
| 121 | +---------------+ | +---------------+ |
| 122 | | mm_struct | |.... | mm_struct | |
| 123 | | | | | | |
| 124 | +---------------+ | +---------------+ |
| 125 | | |
| 126 | + --------------+ |
| 127 | | |
| 128 | +---------------+ +------+--------+ |
| 129 | | page +----------> page_cgroup| |
| 130 | | | | | |
| 131 | +---------------+ +---------------+ |
| 132 | |
| 133 | (Figure 1: Hierarchy of Accounting) |
| 134 | |
| 135 | |
| 136 | Figure 1 shows the important aspects of the controller |
| 137 | |
| 138 | 1. Accounting happens per cgroup |
| 139 | 2. Each mm_struct knows about which cgroup it belongs to |
| 140 | 3. Each page has a pointer to the page_cgroup, which in turn knows the |
| 141 | cgroup it belongs to |
| 142 | |
| 143 | The accounting is done as follows: mem_cgroup_charge() is invoked to setup |
| 144 | the necessary data structures and check if the cgroup that is being charged |
| 145 | is over its limit. If it is then reclaim is invoked on the cgroup. |
| 146 | More details can be found in the reclaim section of this document. |
| 147 | If everything goes well, a page meta-data-structure called page_cgroup is |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 148 | updated. page_cgroup has its own LRU on cgroup. |
| 149 | (*) page_cgroup structure is allocated at boot/memory-hotplug time. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 150 | |
| 151 | 2.2.1 Accounting details |
| 152 | |
KAMEZAWA Hiroyuki | 5b4e655 | 2008-10-18 20:28:10 -0700 | [diff] [blame] | 153 | All mapped anon pages (RSS) and cache pages (Page Cache) are accounted. |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 154 | Some pages which are never reclaimable and will not be on the global LRU |
| 155 | are not accounted. We just account pages under usual VM management. |
KAMEZAWA Hiroyuki | 5b4e655 | 2008-10-18 20:28:10 -0700 | [diff] [blame] | 156 | |
| 157 | RSS pages are accounted at page_fault unless they've already been accounted |
| 158 | for earlier. A file page will be accounted for as Page Cache when it's |
| 159 | inserted into inode (radix-tree). While it's mapped into the page tables of |
| 160 | processes, duplicate accounting is carefully avoided. |
| 161 | |
| 162 | A RSS page is unaccounted when it's fully unmapped. A PageCache page is |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 163 | unaccounted when it's removed from radix-tree. Even if RSS pages are fully |
| 164 | unmapped (by kswapd), they may exist as SwapCache in the system until they |
| 165 | are really freed. Such SwapCaches also also accounted. |
| 166 | A swapped-in page is not accounted until it's mapped. |
| 167 | |
| 168 | Note: The kernel does swapin-readahead and read multiple swaps at once. |
| 169 | This means swapped-in pages may contain pages for other tasks than a task |
| 170 | causing page fault. So, we avoid accounting at swap-in I/O. |
KAMEZAWA Hiroyuki | 5b4e655 | 2008-10-18 20:28:10 -0700 | [diff] [blame] | 171 | |
| 172 | At page migration, accounting information is kept. |
| 173 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 174 | Note: we just account pages-on-LRU because our purpose is to control amount |
| 175 | of used pages; not-on-LRU pages tend to be out-of-control from VM view. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 176 | |
| 177 | 2.3 Shared Page Accounting |
| 178 | |
| 179 | Shared pages are accounted on the basis of the first touch approach. The |
| 180 | cgroup that first touches a page is accounted for the page. The principle |
| 181 | behind this approach is that a cgroup that aggressively uses a shared |
| 182 | page will eventually get charged for it (once it is uncharged from |
| 183 | the cgroup that brought it in -- this will happen on memory pressure). |
| 184 | |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 185 | Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.. |
| 186 | When you do swapoff and make swapped-out pages of shmem(tmpfs) to |
KAMEZAWA Hiroyuki | d13d144 | 2009-01-07 18:07:56 -0800 | [diff] [blame] | 187 | be backed into memory in force, charges for pages are accounted against the |
| 188 | caller of swapoff rather than the users of shmem. |
| 189 | |
| 190 | |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 191 | 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 192 | |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 193 | Swap Extension allows you to record charge for swap. A swapped-in page is |
| 194 | charged back to original page allocator if possible. |
| 195 | |
| 196 | When swap is accounted, following files are added. |
| 197 | - memory.memsw.usage_in_bytes. |
| 198 | - memory.memsw.limit_in_bytes. |
| 199 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 200 | memsw means memory+swap. Usage of memory+swap is limited by |
| 201 | memsw.limit_in_bytes. |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 202 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 203 | Example: Assume a system with 4G of swap. A task which allocates 6G of memory |
| 204 | (by mistake) under 2G memory limitation will use all swap. |
| 205 | In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap. |
| 206 | By using memsw limit, you can avoid system OOM which can be caused by swap |
| 207 | shortage. |
| 208 | |
| 209 | * why 'memory+swap' rather than swap. |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 210 | The global LRU(kswapd) can swap out arbitrary pages. Swap-out means |
| 211 | to move account from memory to swap...there is no change in usage of |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 212 | memory+swap. In other words, when we want to limit the usage of swap without |
| 213 | affecting global LRU, memory+swap limit is better than just limiting swap from |
KAMEZAWA Hiroyuki | 22a668d | 2009-06-17 16:27:19 -0700 | [diff] [blame] | 214 | OS point of view. |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 215 | |
KAMEZAWA Hiroyuki | 22a668d | 2009-06-17 16:27:19 -0700 | [diff] [blame] | 216 | * What happens when a cgroup hits memory.memsw.limit_in_bytes |
| 217 | When a cgroup his memory.memsw.limit_in_bytes, it's useless to do swap-out |
| 218 | in this cgroup. Then, swap-out will not be done by cgroup routine and file |
| 219 | caches are dropped. But as mentioned above, global LRU can do swapout memory |
| 220 | from it for sanity of the system's memory management state. You can't forbid |
| 221 | it by cgroup. |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 222 | |
| 223 | 2.5 Reclaim |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 224 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 225 | Each cgroup maintains a per cgroup LRU which has the same structure as |
| 226 | global VM. When a cgroup goes over its limit, we first try |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 227 | to reclaim memory from the cgroup so as to make space for the new |
| 228 | pages that the cgroup has touched. If the reclaim is unsuccessful, |
| 229 | an OOM routine is invoked to select and kill the bulkiest task in the |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 230 | cgroup. (See 10. OOM Control below.) |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 231 | |
| 232 | The reclaim algorithm has not been modified for cgroups, except that |
| 233 | pages that are selected for reclaiming come from the per cgroup LRU |
| 234 | list. |
| 235 | |
Balbir Singh | 4b3bde4 | 2009-09-23 15:56:32 -0700 | [diff] [blame] | 236 | NOTE: Reclaim does not work for the root cgroup, since we cannot set any |
| 237 | limits on the root cgroup. |
| 238 | |
KAMEZAWA Hiroyuki | daaf1e6 | 2010-03-10 15:22:32 -0800 | [diff] [blame] | 239 | Note2: When panic_on_oom is set to "2", the whole system will panic. |
| 240 | |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 241 | When oom event notifier is registered, event will be delivered. |
| 242 | (See oom_control section) |
| 243 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 244 | 2.6 Locking |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 245 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 246 | lock_page_cgroup()/unlock_page_cgroup() should not be called under |
| 247 | mapping->tree_lock. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 248 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 249 | Other lock order is following: |
| 250 | PG_locked. |
| 251 | mm->page_table_lock |
| 252 | zone->lru_lock |
| 253 | lock_page_cgroup. |
| 254 | In many cases, just lock_page_cgroup() is called. |
| 255 | per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by |
| 256 | zone->lru_lock, it has no lock of its own. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 257 | |
| 258 | 3. User Interface |
| 259 | |
| 260 | 0. Configuration |
| 261 | |
| 262 | a. Enable CONFIG_CGROUPS |
| 263 | b. Enable CONFIG_RESOURCE_COUNTERS |
Balbir Singh | 00f0b82 | 2008-03-04 14:28:39 -0800 | [diff] [blame] | 264 | c. Enable CONFIG_CGROUP_MEM_RES_CTLR |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 265 | d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension) |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 266 | |
| 267 | 1. Prepare the cgroups |
| 268 | # mkdir -p /cgroups |
| 269 | # mount -t cgroup none /cgroups -o memory |
| 270 | |
| 271 | 2. Make the new group and move bash into it |
| 272 | # mkdir /cgroups/0 |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 273 | # echo $$ > /cgroups/0/tasks |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 274 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 275 | Since now we're in the 0 cgroup, we can alter the memory limit: |
Balbir Singh | fb78922 | 2008-03-04 14:28:24 -0800 | [diff] [blame] | 276 | # echo 4M > /cgroups/0/memory.limit_in_bytes |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 277 | |
| 278 | NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo, |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 279 | mega or gigabytes. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes, Gibibytes.) |
| 280 | |
Daisuke Nishimura | c5b947b | 2009-06-17 16:27:20 -0700 | [diff] [blame] | 281 | NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited). |
Balbir Singh | 4b3bde4 | 2009-09-23 15:56:32 -0700 | [diff] [blame] | 282 | NOTE: We cannot set limits on the root cgroup any more. |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 283 | |
| 284 | # cat /cgroups/0/memory.limit_in_bytes |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 285 | 4194304 |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 286 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 287 | We can check the usage: |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 288 | # cat /cgroups/0/memory.usage_in_bytes |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 289 | 1216512 |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 290 | |
| 291 | A successful write to this file does not guarantee a successful set of |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 292 | this limit to the value written into the file. This can be due to a |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 293 | number of factors, such as rounding up to page boundaries or the total |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 294 | availability of memory on the system. The user is required to re-read |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 295 | this file after a write to guarantee the value committed by the kernel. |
| 296 | |
Balbir Singh | fb78922 | 2008-03-04 14:28:24 -0800 | [diff] [blame] | 297 | # echo 1 > memory.limit_in_bytes |
Balbir Singh | 0eea103 | 2008-02-07 00:13:57 -0800 | [diff] [blame] | 298 | # cat memory.limit_in_bytes |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 299 | 4096 |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 300 | |
| 301 | The memory.failcnt field gives the number of times that the cgroup limit was |
| 302 | exceeded. |
| 303 | |
KAMEZAWA Hiroyuki | dfc05c2 | 2008-02-07 00:14:41 -0800 | [diff] [blame] | 304 | The memory.stat file gives accounting information. Now, the number of |
| 305 | caches, RSS and Active pages/Inactive pages are shown. |
| 306 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 307 | 4. Testing |
| 308 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 309 | For testing features and implementation, see memcg_test.txt. |
| 310 | |
| 311 | Performance test is also important. To see pure memory controller's overhead, |
| 312 | testing on tmpfs will give you good numbers of small overheads. |
| 313 | Example: do kernel make on tmpfs. |
| 314 | |
| 315 | Page-fault scalability is also important. At measuring parallel |
| 316 | page fault test, multi-process test may be better than multi-thread |
| 317 | test because it has noise of shared objects/status. |
| 318 | |
| 319 | But the above two are testing extreme situations. |
| 320 | Trying usual test under memory controller is always helpful. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 321 | |
| 322 | 4.1 Troubleshooting |
| 323 | |
| 324 | Sometimes a user might find that the application under a cgroup is |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 325 | terminated by OOM killer. There are several causes for this: |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 326 | |
| 327 | 1. The cgroup limit is too low (just too low to do anything useful) |
| 328 | 2. The user is using anonymous memory and swap is turned off or too low |
| 329 | |
| 330 | A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of |
| 331 | some of the pages cached in the cgroup (page cache pages). |
| 332 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 333 | To know what happens, disable OOM_Kill by 10. OOM Control(see below) and |
| 334 | seeing what happens will be helpful. |
| 335 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 336 | 4.2 Task migration |
| 337 | |
Francis Galiegue | a33f322 | 2010-04-23 00:08:02 +0200 | [diff] [blame] | 338 | When a task migrates from one cgroup to another, its charge is not |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 339 | carried forward by default. The pages allocated from the original cgroup still |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 340 | remain charged to it, the charge is dropped when the page is freed or |
| 341 | reclaimed. |
| 342 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 343 | You can move charges of a task along with task migration. |
| 344 | See 8. "Move charges at task migration" |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 345 | |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 346 | 4.3 Removing a cgroup |
| 347 | |
| 348 | A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a |
| 349 | cgroup might have some charge associated with it, even though all |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 350 | tasks have migrated away from it. (because we charge against pages, not |
| 351 | against tasks.) |
| 352 | |
| 353 | Such charges are freed or moved to their parent. At moving, both of RSS |
| 354 | and CACHES are moved to parent. |
| 355 | rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also. |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 356 | |
KAMEZAWA Hiroyuki | 8c7c6e34 | 2009-01-07 18:08:00 -0800 | [diff] [blame] | 357 | Charges recorded in swap information is not updated at removal of cgroup. |
| 358 | Recorded information is discarded and a cgroup which uses swap (swapcache) |
| 359 | will be charged as a new owner of it. |
| 360 | |
| 361 | |
KAMEZAWA Hiroyuki | c1e862c | 2009-01-07 18:07:55 -0800 | [diff] [blame] | 362 | 5. Misc. interfaces. |
| 363 | |
| 364 | 5.1 force_empty |
| 365 | memory.force_empty interface is provided to make cgroup's memory usage empty. |
| 366 | You can use this interface only when the cgroup has no tasks. |
| 367 | When writing anything to this |
| 368 | |
| 369 | # echo 0 > memory.force_empty |
| 370 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 371 | Almost all pages tracked by this memory cgroup will be unmapped and freed. |
| 372 | Some pages cannot be freed because they are locked or in-use. Such pages are |
| 373 | moved to parent and this cgroup will be empty. This may return -EBUSY if |
| 374 | VM is too busy to free/move all pages immediately. |
KAMEZAWA Hiroyuki | c1e862c | 2009-01-07 18:07:55 -0800 | [diff] [blame] | 375 | |
| 376 | Typical use case of this interface is that calling this before rmdir(). |
| 377 | Because rmdir() moves all pages to parent, some out-of-use page caches can be |
| 378 | moved to the parent. If you want to avoid that, force_empty will be useful. |
| 379 | |
KOSAKI Motohiro | 7f016ee | 2009-01-07 18:08:22 -0800 | [diff] [blame] | 380 | 5.2 stat file |
KOSAKI Motohiro | 7f016ee | 2009-01-07 18:08:22 -0800 | [diff] [blame] | 381 | |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 382 | memory.stat file includes following statistics |
KOSAKI Motohiro | 7f016ee | 2009-01-07 18:08:22 -0800 | [diff] [blame] | 383 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 384 | # per-memory cgroup local status |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 385 | cache - # of bytes of page cache memory. |
| 386 | rss - # of bytes of anonymous and swap cache memory. |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 387 | mapped_file - # of bytes of mapped file (includes tmpfs/shmem) |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 388 | pgpgin - # of pages paged in (equivalent to # of charging events). |
| 389 | pgpgout - # of pages paged out (equivalent to # of uncharging events). |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 390 | swap - # of bytes of swap usage |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 391 | inactive_anon - # of bytes of anonymous memory and swap cache memory on |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 392 | LRU list. |
| 393 | active_anon - # of bytes of anonymous and swap cache memory on active |
| 394 | inactive LRU list. |
| 395 | inactive_file - # of bytes of file-backed memory on inactive LRU list. |
| 396 | active_file - # of bytes of file-backed memory on active LRU list. |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 397 | unevictable - # of bytes of memory that cannot be reclaimed (mlocked etc). |
| 398 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 399 | # status considering hierarchy (see memory.use_hierarchy settings) |
| 400 | |
| 401 | hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy |
| 402 | under which the memory cgroup is |
| 403 | hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to |
| 404 | hierarchy under which memory cgroup is. |
| 405 | |
| 406 | total_cache - sum of all children's "cache" |
| 407 | total_rss - sum of all children's "rss" |
| 408 | total_mapped_file - sum of all children's "cache" |
| 409 | total_pgpgin - sum of all children's "pgpgin" |
| 410 | total_pgpgout - sum of all children's "pgpgout" |
| 411 | total_swap - sum of all children's "swap" |
| 412 | total_inactive_anon - sum of all children's "inactive_anon" |
| 413 | total_active_anon - sum of all children's "active_anon" |
| 414 | total_inactive_file - sum of all children's "inactive_file" |
| 415 | total_active_file - sum of all children's "active_file" |
| 416 | total_unevictable - sum of all children's "unevictable" |
| 417 | |
| 418 | # The following additional stats are dependent on CONFIG_DEBUG_VM. |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 419 | |
| 420 | inactive_ratio - VM internal parameter. (see mm/page_alloc.c) |
| 421 | recent_rotated_anon - VM internal parameter. (see mm/vmscan.c) |
| 422 | recent_rotated_file - VM internal parameter. (see mm/vmscan.c) |
| 423 | recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) |
| 424 | recent_scanned_file - VM internal parameter. (see mm/vmscan.c) |
| 425 | |
| 426 | Memo: |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 427 | recent_rotated means recent frequency of LRU rotation. |
| 428 | recent_scanned means recent # of scans to LRU. |
KOSAKI Motohiro | 7f016ee | 2009-01-07 18:08:22 -0800 | [diff] [blame] | 429 | showing for better debug please see the code for meanings. |
| 430 | |
Bharata B Rao | c863d83 | 2009-04-13 14:40:15 -0700 | [diff] [blame] | 431 | Note: |
| 432 | Only anonymous and swap cache memory is listed as part of 'rss' stat. |
| 433 | This should not be confused with the true 'resident set size' or the |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 434 | amount of physical memory used by the cgroup. |
| 435 | 'rss + file_mapped" will give you resident set size of cgroup. |
| 436 | (Note: file and shmem may be shared among other cgroups. In that case, |
| 437 | file_mapped is accounted only when the memory cgroup is owner of page |
| 438 | cache.) |
KOSAKI Motohiro | 7f016ee | 2009-01-07 18:08:22 -0800 | [diff] [blame] | 439 | |
KOSAKI Motohiro | a7885eb | 2009-01-07 18:08:24 -0800 | [diff] [blame] | 440 | 5.3 swappiness |
KOSAKI Motohiro | a7885eb | 2009-01-07 18:08:24 -0800 | [diff] [blame] | 441 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 442 | Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. |
KOSAKI Motohiro | a7885eb | 2009-01-07 18:08:24 -0800 | [diff] [blame] | 443 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 444 | Following cgroups' swappiness can't be changed. |
| 445 | - root cgroup (uses /proc/sys/vm/swappiness). |
| 446 | - a cgroup which uses hierarchy and it has other cgroup(s) below it. |
| 447 | - a cgroup which uses hierarchy and not the root of hierarchy. |
| 448 | |
| 449 | 5.4 failcnt |
| 450 | |
| 451 | A memory cgroup provides memory.failcnt and memory.memsw.failcnt files. |
| 452 | This failcnt(== failure count) shows the number of times that a usage counter |
| 453 | hit its limit. When a memory cgroup hits a limit, failcnt increases and |
| 454 | memory under it will be reclaimed. |
| 455 | |
| 456 | You can reset failcnt by writing 0 to failcnt file. |
| 457 | # echo 0 > .../memory.failcnt |
KOSAKI Motohiro | a7885eb | 2009-01-07 18:08:24 -0800 | [diff] [blame] | 458 | |
Daisuke Nishimura | a111c96 | 2011-04-27 15:26:48 -0700 | [diff] [blame] | 459 | 5.5 usage_in_bytes |
| 460 | |
| 461 | For efficiency, as other kernel components, memory cgroup uses some optimization |
| 462 | to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the |
| 463 | method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz |
| 464 | value for efficient access. (Of course, when necessary, it's synchronized.) |
| 465 | If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP) |
| 466 | value in memory.stat(see 5.2). |
| 467 | |
Ying Han | 50c35e5 | 2011-06-15 15:08:16 -0700 | [diff] [blame] | 468 | 5.6 numa_stat |
| 469 | |
| 470 | This is similar to numa_maps but operates on a per-memcg basis. This is |
| 471 | useful for providing visibility into the numa locality information within |
| 472 | an memcg since the pages are allowed to be allocated from any physical |
| 473 | node. One of the usecases is evaluating application performance by |
| 474 | combining this information with the application's cpu allocation. |
| 475 | |
| 476 | We export "total", "file", "anon" and "unevictable" pages per-node for |
| 477 | each memcg. The ouput format of memory.numa_stat is: |
| 478 | |
| 479 | total=<total pages> N0=<node 0 pages> N1=<node 1 pages> ... |
| 480 | file=<total file pages> N0=<node 0 pages> N1=<node 1 pages> ... |
| 481 | anon=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ... |
| 482 | unevictable=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ... |
| 483 | |
| 484 | And we have total = file + anon + unevictable. |
| 485 | |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 486 | 6. Hierarchy support |
KAMEZAWA Hiroyuki | c1e862c | 2009-01-07 18:07:55 -0800 | [diff] [blame] | 487 | |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 488 | The memory controller supports a deep hierarchy and hierarchical accounting. |
| 489 | The hierarchy is created by creating the appropriate cgroups in the |
| 490 | cgroup filesystem. Consider for example, the following cgroup filesystem |
| 491 | hierarchy |
| 492 | |
| 493 | root |
| 494 | / | \ |
| 495 | / | \ |
| 496 | a b c |
| 497 | | \ |
| 498 | | \ |
| 499 | d e |
| 500 | |
| 501 | In the diagram above, with hierarchical accounting enabled, all memory |
| 502 | usage of e, is accounted to its ancestors up until the root (i.e, c and root), |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 503 | that has memory.use_hierarchy enabled. If one of the ancestors goes over its |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 504 | limit, the reclaim algorithm reclaims from the tasks in the ancestor and the |
| 505 | children of the ancestor. |
| 506 | |
| 507 | 6.1 Enabling hierarchical accounting and reclaim |
| 508 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 509 | A memory cgroup by default disables the hierarchy feature. Support |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 510 | can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup |
| 511 | |
| 512 | # echo 1 > memory.use_hierarchy |
| 513 | |
| 514 | The feature can be disabled by |
| 515 | |
| 516 | # echo 0 > memory.use_hierarchy |
| 517 | |
Greg Thelen | 689bca3 | 2011-02-16 17:51:23 -0800 | [diff] [blame] | 518 | NOTE1: Enabling/disabling will fail if either the cgroup already has other |
| 519 | cgroups created below it, or if the parent cgroup has use_hierarchy |
| 520 | enabled. |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 521 | |
KAMEZAWA Hiroyuki | daaf1e6 | 2010-03-10 15:22:32 -0800 | [diff] [blame] | 522 | NOTE2: When panic_on_oom is set to "2", the whole system will panic in |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 523 | case of an OOM event in any cgroup. |
Balbir Singh | 52bc0d8 | 2009-01-07 18:08:03 -0800 | [diff] [blame] | 524 | |
Balbir Singh | a6df636 | 2009-09-23 15:56:34 -0700 | [diff] [blame] | 525 | 7. Soft limits |
| 526 | |
| 527 | Soft limits allow for greater sharing of memory. The idea behind soft limits |
| 528 | is to allow control groups to use as much of the memory as needed, provided |
| 529 | |
| 530 | a. There is no memory contention |
| 531 | b. They do not exceed their hard limit |
| 532 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 533 | When the system detects memory contention or low memory, control groups |
Balbir Singh | a6df636 | 2009-09-23 15:56:34 -0700 | [diff] [blame] | 534 | are pushed back to their soft limits. If the soft limit of each control |
| 535 | group is very high, they are pushed back as much as possible to make |
| 536 | sure that one control group does not starve the others of memory. |
| 537 | |
| 538 | Please note that soft limits is a best effort feature, it comes with |
| 539 | no guarantees, but it does its best to make sure that when memory is |
| 540 | heavily contended for, memory is allocated based on the soft limit |
| 541 | hints/setup. Currently soft limit based reclaim is setup such that |
| 542 | it gets invoked from balance_pgdat (kswapd). |
| 543 | |
| 544 | 7.1 Interface |
| 545 | |
| 546 | Soft limits can be setup by using the following commands (in this example we |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 547 | assume a soft limit of 256 MiB) |
Balbir Singh | a6df636 | 2009-09-23 15:56:34 -0700 | [diff] [blame] | 548 | |
| 549 | # echo 256M > memory.soft_limit_in_bytes |
| 550 | |
| 551 | If we want to change this to 1G, we can at any time use |
| 552 | |
| 553 | # echo 1G > memory.soft_limit_in_bytes |
| 554 | |
| 555 | NOTE1: Soft limits take effect over a long period of time, since they involve |
| 556 | reclaiming memory for balancing between memory cgroups |
| 557 | NOTE2: It is recommended to set the soft limit always below the hard limit, |
| 558 | otherwise the hard limit will take precedence. |
| 559 | |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 560 | 8. Move charges at task migration |
| 561 | |
| 562 | Users can move charges associated with a task along with task migration, that |
| 563 | is, uncharge task's pages from the old cgroup and charge them to the new cgroup. |
Daisuke Nishimura | 0249144 | 2010-03-10 15:22:17 -0800 | [diff] [blame] | 564 | This feature is not supported in !CONFIG_MMU environments because of lack of |
| 565 | page tables. |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 566 | |
| 567 | 8.1 Interface |
| 568 | |
| 569 | This feature is disabled by default. It can be enabled(and disabled again) by |
| 570 | writing to memory.move_charge_at_immigrate of the destination cgroup. |
| 571 | |
| 572 | If you want to enable it: |
| 573 | |
| 574 | # echo (some positive value) > memory.move_charge_at_immigrate |
| 575 | |
| 576 | Note: Each bits of move_charge_at_immigrate has its own meaning about what type |
| 577 | of charges should be moved. See 8.2 for details. |
| 578 | Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread |
| 579 | group. |
| 580 | Note: If we cannot find enough space for the task in the destination cgroup, we |
| 581 | try to make space by reclaiming memory. Task migration may fail if we |
| 582 | cannot make enough space. |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 583 | Note: It can take several seconds if you move charges much. |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 584 | |
| 585 | And if you want disable it again: |
| 586 | |
| 587 | # echo 0 > memory.move_charge_at_immigrate |
| 588 | |
| 589 | 8.2 Type of charges which can be move |
| 590 | |
| 591 | Each bits of move_charge_at_immigrate has its own meaning about what type of |
Daisuke Nishimura | 87946a7 | 2010-05-26 14:42:39 -0700 | [diff] [blame] | 592 | charges should be moved. But in any cases, it must be noted that an account of |
| 593 | a page or a swap can be moved only when it is charged to the task's current(old) |
| 594 | memory cgroup. |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 595 | |
| 596 | bit | what type of charges would be moved ? |
| 597 | -----+------------------------------------------------------------------------ |
| 598 | 0 | A charge of an anonymous page(or swap of it) used by the target task. |
| 599 | | Those pages and swaps must be used only by the target task. You must |
| 600 | | enable Swap Extension(see 2.4) to enable move of swap charges. |
Daisuke Nishimura | 87946a7 | 2010-05-26 14:42:39 -0700 | [diff] [blame] | 601 | -----+------------------------------------------------------------------------ |
| 602 | 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 603 | | and swaps of tmpfs file) mmapped by the target task. Unlike the case of |
Daisuke Nishimura | 87946a7 | 2010-05-26 14:42:39 -0700 | [diff] [blame] | 604 | | anonymous pages, file pages(and swaps) in the range mmapped by the task |
| 605 | | will be moved even if the task hasn't done page fault, i.e. they might |
| 606 | | not be the task's "RSS", but other task's "RSS" that maps the same file. |
| 607 | | And mapcount of the page is ignored(the page can be moved even if |
| 608 | | page_mapcount(page) > 1). You must enable Swap Extension(see 2.4) to |
| 609 | | enable move of swap charges. |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 610 | |
| 611 | 8.3 TODO |
| 612 | |
Daisuke Nishimura | 7dc74be | 2010-03-10 15:22:13 -0800 | [diff] [blame] | 613 | - Implement madvise(2) to let users decide the vma to be moved or not to be |
| 614 | moved. |
| 615 | - All of moving charge operations are done under cgroup_mutex. It's not good |
| 616 | behavior to hold the mutex too long, so we may need some trick. |
| 617 | |
Kirill A. Shutemov | 2e72b63 | 2010-03-10 15:22:24 -0800 | [diff] [blame] | 618 | 9. Memory thresholds |
| 619 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 620 | Memory cgroup implements memory thresholds using cgroups notification |
Kirill A. Shutemov | 2e72b63 | 2010-03-10 15:22:24 -0800 | [diff] [blame] | 621 | API (see cgroups.txt). It allows to register multiple memory and memsw |
| 622 | thresholds and gets notifications when it crosses. |
| 623 | |
| 624 | To register a threshold application need: |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 625 | - create an eventfd using eventfd(2); |
| 626 | - open memory.usage_in_bytes or memory.memsw.usage_in_bytes; |
| 627 | - write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to |
| 628 | cgroup.event_control. |
Kirill A. Shutemov | 2e72b63 | 2010-03-10 15:22:24 -0800 | [diff] [blame] | 629 | |
| 630 | Application will be notified through eventfd when memory usage crosses |
| 631 | threshold in any direction. |
| 632 | |
| 633 | It's applicable for root and non-root cgroup. |
| 634 | |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 635 | 10. OOM Control |
| 636 | |
KAMEZAWA Hiroyuki | 3c11ecf | 2010-05-26 14:42:37 -0700 | [diff] [blame] | 637 | memory.oom_control file is for OOM notification and other controls. |
| 638 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 639 | Memory cgroup implements OOM notifier using cgroup notification |
| 640 | API (See cgroups.txt). It allows to register multiple OOM notification |
| 641 | delivery and gets notification when OOM happens. |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 642 | |
| 643 | To register a notifier, application need: |
| 644 | - create an eventfd using eventfd(2) |
| 645 | - open memory.oom_control file |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 646 | - write string like "<event_fd> <fd of memory.oom_control>" to |
| 647 | cgroup.event_control |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 648 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 649 | Application will be notified through eventfd when OOM happens. |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 650 | OOM notification doesn't work for root cgroup. |
| 651 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 652 | You can disable OOM-killer by writing "1" to memory.oom_control file, as: |
| 653 | |
KAMEZAWA Hiroyuki | 3c11ecf | 2010-05-26 14:42:37 -0700 | [diff] [blame] | 654 | #echo 1 > memory.oom_control |
| 655 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 656 | This operation is only allowed to the top cgroup of sub-hierarchy. |
| 657 | If OOM-killer is disabled, tasks under cgroup will hang/sleep |
| 658 | in memory cgroup's OOM-waitqueue when they request accountable memory. |
KAMEZAWA Hiroyuki | 3c11ecf | 2010-05-26 14:42:37 -0700 | [diff] [blame] | 659 | |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 660 | For running them, you have to relax the memory cgroup's OOM status by |
KAMEZAWA Hiroyuki | 3c11ecf | 2010-05-26 14:42:37 -0700 | [diff] [blame] | 661 | * enlarge limit or reduce usage. |
| 662 | To reduce usage, |
| 663 | * kill some tasks. |
| 664 | * move some tasks to other group with account migration. |
| 665 | * remove some files (on tmpfs?) |
| 666 | |
| 667 | Then, stopped tasks will work again. |
| 668 | |
| 669 | At reading, current status of OOM is shown. |
| 670 | oom_kill_disable 0 or 1 (if 1, oom-killer is disabled) |
KAMEZAWA Hiroyuki | dc10e28 | 2010-05-26 14:42:40 -0700 | [diff] [blame] | 671 | under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may |
KAMEZAWA Hiroyuki | 3c11ecf | 2010-05-26 14:42:37 -0700 | [diff] [blame] | 672 | be stopped.) |
KAMEZAWA Hiroyuki | 9490ff2 | 2010-05-26 14:42:36 -0700 | [diff] [blame] | 673 | |
| 674 | 11. TODO |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 675 | |
| 676 | 1. Add support for accounting huge pages (as a separate controller) |
KAMEZAWA Hiroyuki | dfc05c2 | 2008-02-07 00:14:41 -0800 | [diff] [blame] | 677 | 2. Make per-cgroup scanner reclaim not-shared pages first |
| 678 | 3. Teach controller to account for shared-pages |
KAMEZAWA Hiroyuki | 628f423 | 2008-07-25 01:47:20 -0700 | [diff] [blame] | 679 | 4. Start reclamation in the background when the limit is |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 680 | not yet hit but the usage is getting closer |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 681 | |
| 682 | Summary |
| 683 | |
| 684 | Overall, the memory controller has been a stable controller and has been |
| 685 | commented and discussed quite extensively in the community. |
| 686 | |
| 687 | References |
| 688 | |
| 689 | 1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/ |
| 690 | 2. Singh, Balbir. Memory Controller (RSS Control), |
| 691 | http://lwn.net/Articles/222762/ |
| 692 | 3. Emelianov, Pavel. Resource controllers based on process cgroups |
| 693 | http://lkml.org/lkml/2007/3/6/198 |
| 694 | 4. Emelianov, Pavel. RSS controller based on process cgroups (v2) |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 695 | http://lkml.org/lkml/2007/4/9/78 |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 696 | 5. Emelianov, Pavel. RSS controller based on process cgroups (v3) |
| 697 | http://lkml.org/lkml/2007/5/30/244 |
| 698 | 6. Menage, Paul. Control Groups v10, http://lwn.net/Articles/236032/ |
| 699 | 7. Vaidyanathan, Srinivasan, Control Groups: Pagecache accounting and control |
| 700 | subsystem (v3), http://lwn.net/Articles/235534/ |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 701 | 8. Singh, Balbir. RSS controller v2 test results (lmbench), |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 702 | http://lkml.org/lkml/2007/5/17/232 |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 703 | 9. Singh, Balbir. RSS controller v2 AIM9 results |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 704 | http://lkml.org/lkml/2007/5/18/1 |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 705 | 10. Singh, Balbir. Memory controller v6 test results, |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 706 | http://lkml.org/lkml/2007/8/19/36 |
Li Zefan | 2324c5d | 2008-02-23 15:24:12 -0800 | [diff] [blame] | 707 | 11. Singh, Balbir. Memory controller introduction (v6), |
| 708 | http://lkml.org/lkml/2007/8/17/69 |
Balbir Singh | 1b6df3a | 2008-02-07 00:13:46 -0800 | [diff] [blame] | 709 | 12. Corbet, Jonathan, Controlling memory use in cgroups, |
| 710 | http://lwn.net/Articles/243795/ |