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authorPaul Menage <menage@google.com>2007-10-18 23:39:36 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-19 11:53:36 -0700
commit817929ec274bcfe771586d338bb31d1659615686 (patch)
tree5a96ed1afd308016e8720437a00bf2f114e907cb /Documentation/cgroups.txt
parenta424316ca154317367c7ddf89997d1c80e4a8051 (diff)
Task Control Groups: shared cgroup subsystem group arrays
Replace the struct css_set embedded in task_struct with a pointer; all tasks that have the same set of memberships across all hierarchies will share a css_set object, and will be linked via their css_sets field to the "tasks" list_head in the css_set. Assuming that many tasks share the same cgroup assignments, this reduces overall space usage and keeps the size of the task_struct down (three pointers added to task_struct compared to a non-cgroups kernel, no matter how many subsystems are registered). [akpm@linux-foundation.org: fix a printk] [akpm@linux-foundation.org: build fix] Signed-off-by: Paul Menage <menage@google.com> Cc: Serge E. Hallyn <serue@us.ibm.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Paul Jackson <pj@sgi.com> Cc: Kirill Korotaev <dev@openvz.org> Cc: Herbert Poetzl <herbert@13thfloor.at> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Cc: Serge E. Hallyn <serue@us.ibm.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Paul Jackson <pj@sgi.com> Cc: Kirill Korotaev <dev@openvz.org> Cc: Herbert Poetzl <herbert@13thfloor.at> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/cgroups.txt')
-rw-r--r--Documentation/cgroups.txt14
1 files changed, 13 insertions, 1 deletions
diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
index 553727cc9944..98a26f81fa75 100644
--- a/Documentation/cgroups.txt
+++ b/Documentation/cgroups.txt
@@ -176,7 +176,9 @@ Control Groups extends the kernel as follows:
subsystem state is something that's expected to happen frequently
and in performance-critical code, whereas operations that require a
task's actual cgroup assignments (in particular, moving between
- cgroups) are less common.
+ cgroups) are less common. A linked list runs through the cg_list
+ field of each task_struct using the css_set, anchored at
+ css_set->tasks.
- A cgroup hierarchy filesystem can be mounted for browsing and
manipulation from user space.
@@ -252,6 +254,16 @@ linear search to locate an appropriate existing css_set, so isn't
very efficient. A future version will use a hash table for better
performance.
+To allow access from a cgroup to the css_sets (and hence tasks)
+that comprise it, a set of cg_cgroup_link objects form a lattice;
+each cg_cgroup_link is linked into a list of cg_cgroup_links for
+a single cgroup on its cont_link_list field, and a list of
+cg_cgroup_links for a single css_set on its cg_link_list.
+
+Thus the set of tasks in a cgroup can be listed by iterating over
+each css_set that references the cgroup, and sub-iterating over
+each css_set's task set.
+
The use of a Linux virtual file system (vfs) to represent the
cgroup hierarchy provides for a familiar permission and name space
for cgroups, with a minimum of additional kernel code.