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cgroup: use bitmask to filter for_each_subsys

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Add a new macro for_each_subsys_which that allows all enabled cgroup
subsystems to be filtered by a bitmask, such that mask & (1 << ssid)
determines if the subsystem is to be processed in the loop body (where
ssid is the unique id of the subsystem).

Also replace the need_forkexit_callback with two separate bitmasks for
each callback to make (ss->{fork,exit}) checks unnecessary.

tj: add a short comment for "if (!CGROUP_SUBSYS_COUNT)".

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
This commit is contained in:
Aleksa Sarai 2015-06-06 10:02:14 +10:00 committed by Tejun Heo
parent c80ef9e0c0
commit cb4a316752
2 changed files with 35 additions and 20 deletions
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2
include/linux/cgroup-defs.h
View file

@ -490,6 +490,8 @@ static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
#else /* CONFIG_CGROUPS */
#define CGROUP_SUBSYS_COUNT 0
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {}
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}

43
kernel/cgroup.c
View file

@ -178,12 +178,13 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
*/
static u64 css_serial_nr_next = 1;
/* This flag indicates whether tasks in the fork and exit paths should
* check for fork/exit handlers to call. This avoids us having to do
* extra work in the fork/exit path if none of the subsystems need to
* be called.
/*
* These bitmask flags indicate whether tasks in the fork and exit paths have
* fork/exit handlers to call. This avoids us having to do extra work in the
* fork/exit path to check which subsystems have fork/exit callbacks.
*/
static int need_forkexit_callback __read_mostly;
static unsigned long have_fork_callback __read_mostly;
static unsigned long have_exit_callback __read_mostly;
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@ -412,6 +413,24 @@ static int notify_on_release(const struct cgroup *cgrp)
for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
(((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
/**
* for_each_subsys_which - filter for_each_subsys with a bitmask
* @ss: the iteration cursor
* @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
* @ss_maskp: a pointer to the bitmask
*
* The block will only run for cases where the ssid-th bit (1 << ssid) of
* mask is set to 1.
*/
#define for_each_subsys_which(ss, ssid, ss_maskp) \
if (!CGROUP_SUBSYS_COUNT) /* to avoid spurious gcc warning */ \
; \
else \
for_each_set_bit(ssid, ss_maskp, CGROUP_SUBSYS_COUNT) \
if (((ss) = cgroup_subsys[ssid]) && false) \
break; \
else
/* iterate across the hierarchies */
#define for_each_root(root) \
list_for_each_entry((root), &cgroup_roots, root_list)
@ -4914,7 +4933,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
* init_css_set is in the subsystem's root cgroup. */
init_css_set.subsys[ss->id] = css;
need_forkexit_callback |= ss->fork || ss->exit;
have_fork_callback |= (bool)ss->fork << ss->id;
have_exit_callback |= (bool)ss->exit << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@ -5225,11 +5245,8 @@ void cgroup_post_fork(struct task_struct *child)
* css_set; otherwise, @child might change state between ->fork()
* and addition to css_set.
*/
if (need_forkexit_callback) {
for_each_subsys(ss, i)
if (ss->fork)
for_each_subsys_which(ss, i, &have_fork_callback)
ss->fork(child);
}
}
/**
@ -5273,17 +5290,13 @@ void cgroup_exit(struct task_struct *tsk)
cset = task_css_set(tsk);
RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
if (need_forkexit_callback) {
/* see cgroup_post_fork() for details */
for_each_subsys(ss, i) {
if (ss->exit) {
for_each_subsys_which(ss, i, &have_exit_callback) {
struct cgroup_subsys_state *old_css = cset->subsys[i];
struct cgroup_subsys_state *css = task_css(tsk, i);
ss->exit(css, old_css, tsk);
}
}
}
if (put_cset)
put_css_set(cset);