staging: android: lowmemkiller: Substantially reduce overhead during reclaim
This patch optimizes lowmemkiller to not do any work when it has an outstanding
kill-request. This greatly reduces the pressure on the task_list lock
(improving interactivity), as well as improving the vmscan performance
when under heavy memory pressure (by up to 20x in tests).
Note: For this enhancement to work, you need CONFIG_PROFILING
Signed-off-by: San Mehat <san@google.com>
diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index 8372178..4523093 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -34,6 +34,8 @@
#include <linux/mm.h>
#include <linux/oom.h>
#include <linux/sched.h>
+#include <linux/profile.h>
+#include <linux/notifier.h>
static uint32_t lowmem_debug_level = 2;
static int lowmem_adj[6] = {
@@ -51,12 +53,32 @@
};
static int lowmem_minfree_size = 4;
+static struct task_struct *lowmem_deathpending;
+
#define lowmem_print(level, x...) \
do { \
if (lowmem_debug_level >= (level)) \
printk(x); \
} while (0)
+static int
+task_notify_func(struct notifier_block *self, unsigned long val, void *data);
+
+static struct notifier_block task_nb = {
+ .notifier_call = task_notify_func,
+};
+
+static int
+task_notify_func(struct notifier_block *self, unsigned long val, void *data)
+{
+ struct task_struct *task = data;
+ if (task == lowmem_deathpending) {
+ lowmem_deathpending = NULL;
+ task_handoff_unregister(&task_nb);
+ }
+ return NOTIFY_OK;
+}
+
static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
{
struct task_struct *p;
@@ -71,6 +93,18 @@
int other_free = global_page_state(NR_FREE_PAGES);
int other_file = global_page_state(NR_FILE_PAGES);
+ /*
+ * If we already have a death outstanding, then
+ * bail out right away; indicating to vmscan
+ * that we have nothing further to offer on
+ * this pass.
+ *
+ * Note: Currently you need CONFIG_PROFILING
+ * for this to work correctly.
+ */
+ if (lowmem_deathpending)
+ return 0;
+
if (lowmem_adj_size < array_size)
array_size = lowmem_adj_size;
if (lowmem_minfree_size < array_size)
@@ -142,6 +176,15 @@
lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
selected->pid, selected->comm,
selected_oom_adj, selected_tasksize);
+ /*
+ * If CONFIG_PROFILING is off, then task_handoff_register()
+ * is a nop. In that case we don't want to stall the killer
+ * by setting lowmem_deathpending.
+ */
+#ifdef CONFIG_PROFILING
+ lowmem_deathpending = selected;
+ task_handoff_register(&task_nb);
+#endif
force_sig(SIGKILL, selected);
rem -= selected_tasksize;
}