[PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost
Currently, we get the vm_swappiness via vmscan_swappiness(), which
calls global_reclaim() to check if this is a global reclaim.
Besides, the current implementation of global_reclaim() always returns
true for the !CONFIG_MEGCG case, and judges the other case by checking
whether scan_control->target_mem_cgroup is null or not.
Thus, we could just use two versions of vmscan_swappiness() based on
MEMCG Kconfig , to eliminate the unnecessary run-time cost for
the !CONFIG_MEMCG at all, and to squash all memcg-related checking
into the CONFIG_MEMCG version.
Signed-off-by: Zhan Jianyu
---
mm/memcontrol.c |6 +-
mm/vmscan.c |9 +++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5792a5..1290320 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1525,9 +1525,13 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup
*memcg)
int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
- struct cgroup *cgrp = memcg->css.cgroup;
+ struct cgroup *cgrp;
+
+ if (!memcg)
+ return vm_swappiness;
/* root ? */
+ cgrp = memcg->css.cgroup;
if (cgrp->parent == NULL)
return vm_swappiness;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2cff0d4..1de652d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1742,12 +1742,17 @@ static unsigned long shrink_list(enum lru_list lru,
unsigned long nr_to_scan,
return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
}
+#ifdef CONFIG_MEMCG
static int vmscan_swappiness(struct scan_control *sc)
{
- if (global_reclaim(sc))
- return vm_swappiness;
return mem_cgroup_swappiness(sc->target_mem_cgroup);
}
+#else
+static int vmscan_swappiness(struct scan_control *sc)
+{
+ return vm_swappiness;
+}
+#endif
enum scan_balance {
SCAN_EQUAL,
--
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[PATCH] Documentation/memory-barriers: fix a error that mistakes a CPU notion in Section Transitivity
The memory-barriers document may has a error in Section TRANSITIVITY.
For transitivity, see a example below, given that
* CPU 2's load from X follows CPU 1's store to X, and
CPU 2's load from Y preceds CPU 3's store to Y.
CPU 1 CPU 2 CPU 3
=== === ===
{ X = 0, Y = 0 }
STORE X=1 LOAD X STORE Y=1
LOAD Y LOAD X
The in CPU 2 is inadquate, because it could _only_ guarantees
that load operation _happen before_ load operation after the barrier, with
respect to CPU 3, which constrained by a general barrier, but provide _NO_
guarantee that CPU 1' store X will happen before the .
Therefore, if this example runs on a system where CPUs 1 and 3 share a store
buffer
or a level of cache, CPU 3 might have early access to CPU 1's writes.
The original text has mistaken CPU 2 for CPU 3, so this patch fixes this, and
adds
a paragraph to explain why a should guarantee this.
Signed-off-by: Zhan Jianyu
---
Documentation/memory-barriers.txt | 11 +--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/Documentation/memory-barriers.txt
b/Documentation/memory-barriers.txt
index fa5d8a9..590a5a9 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -992,6 +992,13 @@ transitivity. Therefore, in the above example, if CPU 2's
load from X
returns 1 and its load from Y returns 0, then CPU 3's load from X must
also return 1.
+The key point is that CPU 1's storing 1 to X preceds CPU 2's loading 1
+from X, and CPU 2's loading 0 from Y preceds CPU 3's storing 1 to Y,
+which implies a ordering that the general barrier in CPU 2 guarantees:
+all store and load operations must happen before those after the barrier
+with respect to view of CPU 3, which constrained by a general barrier, too.
+Thus, CPU 3's load from X must return 1.
+
However, transitivity is -not- guaranteed for read or write barriers.
For example, suppose that CPU 2's general barrier in the above example
is changed to a read barrier as shown below:
@@ -1009,8 +1016,8 @@ and CPU 3's load from X to return 0.
The key point is that although CPU 2's read barrier orders its pair
of loads, it does not guarantee to order CPU 1's store. Therefore, if
-this example runs on a system where CPUs 1 and 2 share a store buffer
-or a level of cache, CPU 2 might have early access to CPU 1's writes.
+this example runs on a system where CPUs 1 and 3 share a store buffer
+or a level of cache, CPU 3 might have early access to CPU 1's writes.
General barriers are therefore required to ensure that all CPUs agree
on the combined order of CPU 1's and CPU 2's accesses.
--
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[PATCH] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost
Currently, we get the vm_swappiness via vmscan_swappiness(), which
calls global_reclaim() to check if this is a global reclaim.
Besides, the current implementation of global_reclaim() always returns
true for the !CONFIG_MEGCG case, and judges the other case by checking
whether scan_control->target_mem_cgroup is null or not.
Thus, we could just use two versions of vmscan_swappiness() based on
MEMCG Kconfig , to eliminate the unnecessary run-time cost for
the !CONFIG_MEMCG at all, and to squash all memcg-related checking
into the CONFIG_MEMCG version.
Signed-off-by: Zhan Jianyu
---
mm/memcontrol.c |6 +-
mm/vmscan.c |9 +++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5792a5..1290320 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1525,9 +1525,13 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup
*memcg)
int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
- struct cgroup *cgrp = memcg->css.cgroup;
+ struct cgroup *cgrp;
+
+ if (!memcg)
+ return vm_swappiness;
/* root ? */
+ cgrp = memcg->css.cgroup;
if (cgrp->parent == NULL)
return vm_swappiness;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2cff0d4..1de652d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1742,12 +1742,17 @@ static unsigned long shrink_list(enum lru_list lru,
unsigned long nr_to_scan,
return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
}
+#ifdef CONFIG_MEMCG
static int vmscan_swappiness(struct scan_control *sc)
{
- if (global_reclaim(sc))
- return vm_swappiness;
return mem_cgroup_swappiness(sc->target_mem_cgroup);
}
+#else
+static int vmscan_swappiness(struct scan_control *sc)
+{
+ return vm_swappiness;
+}
+#endif
enum scan_balance {
SCAN_EQUAL,
--
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[PATCH] mm/vmscan: make global_reclaim() inline
Though Gcc is likely to inline them, we should better
explictly do it manually, and also, this serve to document
this fact.
Signed-off-by: Zhan Jianyu
---
mm/vmscan.c |4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1de652d..1946d7d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -135,12 +135,12 @@ static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);
#ifdef CONFIG_MEMCG
-static bool global_reclaim(struct scan_control *sc)
+static inline bool global_reclaim(struct scan_control *sc)
{
return !sc->target_mem_cgroup;
}
#else
-static bool global_reclaim(struct scan_control *sc)
+static inline bool global_reclaim(struct scan_control *sc)
{
return true;
}
--
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