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Subject[patch v2 3/4] taskstats: Introduce kernel.full_cdata sysctl
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

Version 2
---------
* Implement sysctl instead of adding parallel cdata_acct
* Call __account_cdata() in __exit_signal() without tsk siglock

Description
-----------
Currently the cumulative time accounting in Linux is not complete.
Due to POSIX POSIX.1-2001, the CPU time of processes is not accounted
to the cumulative time of the parents, if the parents ignore SIGCHLD
or have set SA_NOCLDWAIT. This behaviour has the major drawback that
it is not possible to calculate all consumed CPU time of a system by
looking at the current tasks. CPU time can be lost.

This patch adds a new sysctl "kernel.full_cdata" that allows to switch
between the POSIX behavior and complete cumulative accounting.
The default is the POSIX semantics.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
Documentation/sysctl/kernel.txt | 12 ++++++++++++
kernel/exit.c | 13 +++++++++----
kernel/sysctl.c | 10 ++++++++++
3 files changed, 31 insertions(+), 4 deletions(-)

--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -247,6 +247,18 @@ see the hostname(1) man page.

==============================================================

+full_cdata:
+
+With "full_cdata = 0" (default) cumulative resource accounting
+under Linux is done according to POSIX.1-2001: The resource
+counters of processes are not accounted to the cumulative counters
+of their parents, if the parents ignore SIGCHLD or have set
+SA_NOCLDWAIT. With "full_cdata = 1" it is possible to enforce
+that all dead processes without exception are accounted to their
+parents.
+
+==============================================================
+
hotplug:

Path for the hotplug policy agent.
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -57,6 +57,8 @@
#include <asm/pgtable.h>
#include <asm/mmu_context.h>

+int full_cdata_enabled;
+
static void exit_mm(struct task_struct * tsk);

static void __unhash_process(struct task_struct *p, bool group_dead)
@@ -77,7 +79,7 @@ static void __unhash_process(struct task
static void __account_cdata(struct task_struct *p)
{
struct cdata *cd, *pcd, *tcd;
- unsigned long maxrss;
+ unsigned long maxrss, flags;
cputime_t tgutime, tgstime;

/*
@@ -104,7 +106,7 @@ static void __account_cdata(struct task_
tcd = &p->signal->cdata_threads;
cd = &p->signal->cdata_wait;

- spin_lock_irq(&p->real_parent->sighand->siglock);
+ spin_lock_irqsave(&p->real_parent->sighand->siglock, flags);
pcd->utime =
cputime_add(pcd->utime,
cputime_add(tgutime,
@@ -137,7 +139,7 @@ static void __account_cdata(struct task_
pcd->maxrss = maxrss;
task_io_accounting_add(&p->real_parent->signal->ioac, &p->ioac);
task_io_accounting_add(&p->real_parent->signal->ioac, &p->signal->ioac);
- spin_unlock_irq(&p->real_parent->sighand->siglock);
+ spin_unlock_irqrestore(&p->real_parent->sighand->siglock, flags);
}

/*
@@ -150,6 +152,9 @@ static void __exit_signal(struct task_st
struct sighand_struct *sighand;
struct tty_struct *uninitialized_var(tty);

+ if (group_dead && full_cdata_enabled)
+ __account_cdata(tsk);
+
sighand = rcu_dereference_check(tsk->sighand,
rcu_read_lock_held() ||
lockdep_tasklist_lock_is_held());
@@ -1292,7 +1297,7 @@ static int wait_task_zombie(struct wait_
* It can be ptraced but not reparented, check
* !task_detached() to filter out sub-threads.
*/
- if (likely(!traced) && likely(!task_detached(p)))
+ if (likely(!traced) && likely(!task_detached(p)) && !full_cdata_enabled)
__account_cdata(p);

/*
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -85,6 +85,7 @@
#if defined(CONFIG_SYSCTL)

/* External variables not in a header file. */
+extern int full_cdata_enabled;
extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
extern int max_threads;
@@ -963,6 +964,15 @@ static struct ctl_table kern_table[] = {
.proc_handler = proc_dointvec,
},
#endif
+ {
+ .procname = "full_cdata",
+ .data = &full_cdata_enabled,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
/*
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt


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