From 817929ec274bcfe771586d338bb31d1659615686 Mon Sep 17 00:00:00 2001 From: Paul Menage Date: Thu, 18 Oct 2007 23:39:36 -0700 Subject: 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 Cc: Serge E. Hallyn Cc: "Eric W. Biederman" Cc: Dave Hansen Cc: Balbir Singh Cc: Paul Jackson Cc: Kirill Korotaev Cc: Herbert Poetzl Cc: Srivatsa Vaddagiri Cc: Cedric Le Goater Cc: Serge E. Hallyn Cc: "Eric W. Biederman" Cc: Dave Hansen Cc: Balbir Singh Cc: Paul Jackson Cc: Kirill Korotaev Cc: Herbert Poetzl Cc: Srivatsa Vaddagiri Cc: Cedric Le Goater Cc: KAMEZAWA Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/cgroups.txt | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'Documentation/cgroups.txt') diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt index 553727cc994..98a26f81fa7 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. -- cgit v1.2.3