The patch titled
cgroups: add cpu_relax() calls in css_tryget() and cgroup_clear_css_refs()
has been added to the -mm tree. Its filename is
cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs.patch
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------------------------------------------------------
Subject: cgroups: add cpu_relax() calls in css_tryget() and cgroup_clear_css_refs()
From: Paul Menage <menage@xxxxxxxxxx>
css_tryget() and cgroup_clear_css_refs() contain polling loops; these
loops should have cpu_relax calls in them to reduce cross-cache traffic.
Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 1 +
kernel/cgroup.c | 7 +++++--
2 files changed, 6 insertions(+), 2 deletions(-)
diff -puN include/linux/cgroup.h~cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs include/linux/cgroup.h
--- a/include/linux/cgroup.h~cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs
+++ a/include/linux/cgroup.h
@@ -99,6 +99,7 @@ static inline bool css_tryget(struct cgr
while (!atomic_inc_not_zero(&css->refcnt)) {
if (test_bit(CSS_REMOVED, &css->flags))
return false;
+ cpu_relax();
}
return true;
}
diff -puN kernel/cgroup.c~cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs kernel/cgroup.c
--- a/kernel/cgroup.c~cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs
+++ a/kernel/cgroup.c
@@ -2509,7 +2509,7 @@ static int cgroup_clear_css_refs(struct
for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
int refcnt;
- do {
+ while (1) {
/* We can only remove a CSS with a refcnt==1 */
refcnt = atomic_read(&css->refcnt);
if (refcnt > 1) {
@@ -2523,7 +2523,10 @@ static int cgroup_clear_css_refs(struct
* css_tryget() to spin until we set the
* CSS_REMOVED bits or abort
*/
- } while (atomic_cmpxchg(&css->refcnt, refcnt, 0) != refcnt);
+ if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
+ break;
+ cpu_relax();
+ }
}
done:
for_each_subsys(cgrp->root, ss) {
_
Patches currently in -mm which might be from menage@xxxxxxxxxx are
cgroups-use-hierarchy-mutex-in-creation-failure-path.patch
memcg-get-put-parents-at-create-free.patch
memcg-get-put-parents-at-create-free-fix.patch
cgroups-fix-lock-inconsistency-in-cgroup_clone.patch
cgroups-add-cpu_relax-calls-in-css_tryget-and-cgroup_clear_css_refs.patch
linux-next.patch
cgroups-fix-cgrouph-comments.patch
relax-ns_can_attach-checks-to-allow-attaching-to-grandchild-cgroups.patch
cpuset-fix-allocating-page-cache-slab-object-on-the-unallowed-node-when-memory-spread-is-set.patch
cpuset-fix-allocating-page-cache-slab-object-on-the-unallowed-node-when-memory-spread-is-set-checkpatch-fixes.patch
add-a-refcount-check-in-dput.patch
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