-Memory Controller
+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.
Salient features
global LRU; a cgroup on hitting a limit, reclaims from the per
cgroup LRU
-NOTE: Page Cache (unmapped) also includes Swap Cache pages as a subset
-and will not be referred to explicitly in the rest of the documentation.
+NOTE: Swap Cache (unmapped) is not accounted now.
Benefits and Purpose of the memory controller
The memory controller uses the following hierarchy
1. zone->lru_lock is used for selecting pages to be isolated
-2. mem->lru_lock protects the per cgroup LRU
+2. mem->per_zone->lru_lock protects the per cgroup LRU (per zone)
3. lock_page_cgroup() is used to protect page->page_cgroup
3. User Interface
a. Enable CONFIG_CGROUPS
b. Enable CONFIG_RESOURCE_COUNTERS
-c. Enable CONFIG_CGROUP_MEM_CONT
+c. Enable CONFIG_CGROUP_MEM_RES_CTLR
1. Prepare the cgroups
# mkdir -p /cgroups
Since now we're in the 0 cgroup,
We can alter the memory limit:
-# echo -n 6000 > /cgroups/0/memory.limit
+# echo 4M > /cgroups/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.
+
+# cat /cgroups/0/memory.limit_in_bytes
+4194304
+
+NOTE: The interface has now changed to display the usage in bytes
+instead of pages
We can check the usage:
-# cat /cgroups/0/memory.usage
-25
+# cat /cgroups/0/memory.usage_in_bytes
+1216512
+
+A successful write to this file does not guarantee a successful set 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
+this file after a write to guarantee the value committed by the kernel.
+
+# echo 1 > memory.limit_in_bytes
+# cat memory.limit_in_bytes
+4096
The memory.failcnt field gives the number of times that the cgroup limit was
exceeded.
+The memory.stat file gives accounting information. Now, the number of
+caches, RSS and Active pages/Inactive pages are shown.
+
+The memory.force_empty gives an interface to drop *all* charges by force.
+
+# echo 1 > memory.force_empty
+
+will drop all charges in cgroup. Currently, this is maintained for test.
+
4. Testing
Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11].
A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
cgroup might have some charge associated with it, even though all
-tasks have migrated away from it. If some pages are still left, after following
-the steps listed in sections 4.1 and 4.2, check the Swap Cache usage in
-/proc/meminfo to see if the Swap Cache usage is showing up in the
-cgroups memory.usage counter. A simple test of swapoff -a and swapon -a
-should free any pending Swap Cache usage.
-
-4.4 Choosing what to account -- Page Cache (unmapped) vs RSS (mapped)?
-
-The type of memory accounted by the cgroup can be limited to just
-mapped pages by writing "1" to memory.control_type field
-
-echo -n 1 > memory.control_type
+tasks have migrated away from it. Such charges are automatically dropped at
+rmdir() if there are no tasks.
5. TODO
1. Add support for accounting huge pages (as a separate controller)
-2. Improve the user interface to accept/display memory limits in KB or MB
- rather than pages (since page sizes can differ across platforms/machines).
-3. Make cgroup lists per-zone
-4. Make per-cgroup scanner reclaim not-shared pages first
-5. Teach controller to account for shared-pages
-6. Start reclamation when the limit is lowered
-7. Start reclamation in the background when the limit is
+2. Make per-cgroup scanner reclaim not-shared pages first
+3. Teach controller to account for shared-pages
+4. Start reclamation when the limit is lowered
+5. Start reclamation in the background when the limit is
not yet hit but the usage is getting closer
-8. Create per zone LRU lists per cgroup
Summary
3. Emelianov, Pavel. Resource controllers based on process cgroups
http://lkml.org/lkml/2007/3/6/198
4. Emelianov, Pavel. RSS controller based on process cgroups (v2)
- http://lkml.org/lkml/2007/4/9/74
+ http://lkml.org/lkml/2007/4/9/78
5. Emelianov, Pavel. RSS controller based on process cgroups (v3)
http://lkml.org/lkml/2007/5/30/244
6. Menage, Paul. Control Groups v10, http://lwn.net/Articles/236032/
7. Vaidyanathan, Srinivasan, Control Groups: Pagecache accounting and control
subsystem (v3), http://lwn.net/Articles/235534/
-8. Singh, Balbir. RSS controller V2 test results (lmbench),
+8. Singh, Balbir. RSS controller v2 test results (lmbench),
http://lkml.org/lkml/2007/5/17/232
-9. Singh, Balbir. RSS controller V2 AIM9 results
+9. Singh, Balbir. RSS controller v2 AIM9 results
http://lkml.org/lkml/2007/5/18/1
-10. Singh, Balbir. Memory controller v6 results,
+10. Singh, Balbir. Memory controller v6 test results,
http://lkml.org/lkml/2007/8/19/36
-11. Singh, Balbir. Memory controller v6, http://lkml.org/lkml/2007/8/17/69
+11. Singh, Balbir. Memory controller introduction (v6),
+ http://lkml.org/lkml/2007/8/17/69
12. Corbet, Jonathan, Controlling memory use in cgroups,
http://lwn.net/Articles/243795/
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff