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 (file)
--- 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 size_t lowmem_minfree[6] = {
 };
 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 @@ static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
        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 @@ static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
                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;
        }