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Message-ID: <20120626120425.GA10275@otc-wbsnb-06>
Date: Tue, 26 Jun 2012 15:04:26 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
"Dmitry V. Levin" <ldv@...linux.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Doug Ledford <dledford@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
Serge Hallyn <serge.hallyn@...onical.com>,
linux-kernel@...r.kernel.org,
"Kirill A. Shutemov" <kirill@...temov.name>
Subject: [RFC, PATCH] CLONE_NEWIPC and exit_group()
Hi,
Patch to move kern_unmount() out of exit_group() code path is below.
Dmitry, could you check if it's beneficial for your use-case?
Results are not that impressive. Microbenchmark:
#define _GNU_SOURCE
#include <unistd.h>
#include <sched.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
int main(int argc, char *argv[])
{
int i;
for (i = 0; i < 1000; i++) {
if (fork())
continue;
unshare(CLONE_NEWIPC);
exit(0);
}
while (wait(NULL) > 0)
;
return 0;
}
Before:
Performance counter stats for './test' (10 runs):
2645.849247 task-clock # 3.203 CPUs utilized ( +- 3.43% )
2,375 context-switches # 0.001 M/sec ( +- 0.35% )
1,579 CPU-migrations # 0.001 M/sec ( +- 0.90% )
37,516 page-faults # 0.014 M/sec ( +- 0.44% )
5,739,887,800 cycles # 2.169 GHz ( +- 3.50% ) [84.21%]
5,126,092,712 stalled-cycles-frontend # 89.31% frontend cycles idle ( +- 3.78% ) [84.47%]
3,779,607,146 stalled-cycles-backend # 65.85% backend cycles idle ( +- 4.06% ) [68.26%]
1,210,768,660 instructions # 0.21 insns per cycle
# 4.23 stalled cycles per insn ( +- 1.01% ) [86.28%]
213,318,802 branches # 80.624 M/sec ( +- 1.16% ) [84.49%]
2,417,038 branch-misses # 1.13% of all branches ( +- 0.70% ) [84.55%]
0.826165497 seconds time elapsed ( +- 1.26% )
After:
Performance counter stats for './test' (10 runs):
4248.846649 task-clock # 6.370 CPUs utilized ( +- 13.50% )
2,343 context-switches # 0.001 M/sec ( +- 1.51% )
1,624 CPU-migrations # 0.000 M/sec ( +- 2.53% )
37,416 page-faults # 0.009 M/sec ( +- 0.41% )
9,314,096,247 cycles # 2.192 GHz ( +- 13.64% ) [83.75%]
8,482,679,429 stalled-cycles-frontend # 91.07% frontend cycles idle ( +- 14.46% ) [83.79%]
5,807,497,239 stalled-cycles-backend # 62.35% backend cycles idle ( +- 14.79% ) [67.65%]
1,556,594,531 instructions # 0.17 insns per cycle
# 5.45 stalled cycles per insn ( +- 5.41% ) [85.00%]
282,682,358 branches # 66.532 M/sec ( +- 5.56% ) [84.32%]
2,610,583 branch-misses # 0.92% of all branches ( +- 4.42% ) [83.90%]
0.667023551 seconds time elapsed ( +- 12.10% )
Any thoughts if it makes sense?
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 5499c92..1a4cfd8 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -67,6 +67,8 @@ struct ipc_namespace {
/* user_ns which owns the ipc ns */
struct user_namespace *user_ns;
+
+ struct work_struct free_ns_work;
};
extern struct ipc_namespace init_ipc_ns;
diff --git a/ipc/namespace.c b/ipc/namespace.c
index f362298c..edbf885 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -16,6 +16,8 @@
#include "util.h"
+static void free_ns(struct work_struct *work);
+
static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
struct ipc_namespace *old_ns)
{
@@ -27,6 +29,7 @@ static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
return ERR_PTR(-ENOMEM);
atomic_set(&ns->count, 1);
+ INIT_WORK(&ns->free_ns_work, free_ns);
err = mq_init_ns(ns);
if (err) {
kfree(ns);
@@ -116,6 +119,15 @@ static void free_ipc_ns(struct ipc_namespace *ns)
kfree(ns);
}
+static void free_ns(struct work_struct *work)
+{
+ struct ipc_namespace *ns = container_of(work, struct ipc_namespace,
+ free_ns_work);
+
+ mq_put_mnt(ns);
+ free_ipc_ns(ns);
+}
+
/*
* put_ipc_ns - drop a reference to an ipc namespace.
* @ns: the namespace to put
@@ -137,8 +149,7 @@ void put_ipc_ns(struct ipc_namespace *ns)
if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
mq_clear_sbinfo(ns);
spin_unlock(&mq_lock);
- mq_put_mnt(ns);
- free_ipc_ns(ns);
+ schedule_work(&ns->free_ns_work);
}
}
--
Kirill A. Shutemov
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