the core of this patch series.
add /dev/mem_notify device for notification low memory to user process.
<usage examle>
fd = open("/dev/mem_notify", O_RDONLY);
if (fd < 0) {
exit(1);
}
pollfds.fd = fd;
pollfds.events = POLLIN;
pollfds.revents = 0;
err = poll(&pollfds, 1, -1); // wake up at low memory
...
</usage example>
ChangeLog
v5 -> v6:
o improve number of wakeup tasks fomula when task is a few.
Signed-off-by: Marcelo Tosatti <marcelo@xxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
Documentation/devices.txt | 1
drivers/char/mem.c | 5 +
include/linux/mem_notify.h | 42 +++++++++++++++
include/linux/mmzone.h | 1
mm/Makefile | 2
mm/mem_notify.c | 123 +++++++++++++++++++++++++++++++++++++++++++++
mm/page_alloc.c | 1
7 files changed, 174 insertions(+), 1 deletion(-)
Index: b/drivers/char/mem.c
===================================================================
--- a/drivers/char/mem.c 2008-02-03 20:59:43.000000000 +0900
+++ b/drivers/char/mem.c 2008-02-03 21:00:24.000000000 +0900
@@ -26,6 +26,7 @@
#include <linux/bootmem.h>
#include <linux/splice.h>
#include <linux/pfn.h>
+#include <linux/mem_notify.h>
#include <asm/uaccess.h>
#include <asm/io.h>
@@ -869,6 +870,9 @@ static int memory_open(struct inode * in
filp->f_op = &oldmem_fops;
break;
#endif
+ case 13:
+ filp->f_op = &mem_notify_fops;
+ break;
default:
return -ENXIO;
}
@@ -901,6 +905,7 @@ static const struct {
#ifdef CONFIG_CRASH_DUMP
{12,"oldmem", S_IRUSR | S_IWUSR | S_IRGRP, &oldmem_fops},
#endif
+ {13, "mem_notify", S_IRUGO, &mem_notify_fops},
};
static struct class *mem_class;
Index: b/include/linux/mem_notify.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ b/include/linux/mem_notify.h 2008-02-03 21:01:41.000000000 +0900
@@ -0,0 +1,42 @@
+/*
+ * Notify applications of memory pressure via /dev/mem_notify
+ *
+ * Copyright (C) 2008 Marcelo Tosatti <marcelo@xxxxxxxxx>,
+ * KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
+ *
+ * Released under the GPL, see the file COPYING for details.
+ */
+
+#ifndef _LINUX_MEM_NOTIFY_H
+#define _LINUX_MEM_NOTIFY_H
+
+#define MEM_NOTIFY_FREQ (HZ/5)
+
+extern atomic_long_t last_mem_notify;
+extern struct file_operations mem_notify_fops;
+
+extern void __memory_pressure_notify(struct zone *zone, int pressure);
+
+static inline void memory_pressure_notify(struct zone *zone, int pressure)
+{
+ unsigned long target;
+ unsigned long pages_high, pages_free, pages_reserve;
+
+ if (pressure) {
+ target = atomic_long_read(&last_mem_notify) + MEM_NOTIFY_FREQ;
+ if (likely(time_before(jiffies, target)))
+ return;
+
+ pages_high = zone->pages_high;
+ pages_free = zone_page_state(zone, NR_FREE_PAGES);
+ pages_reserve = zone->lowmem_reserve[MAX_NR_ZONES-1];
+ if (unlikely(pages_free > (pages_high+pages_reserve)*2))
+ return;
+
+ } else if (likely(!zone->mem_notify_status))
+ return;
+
+ __memory_pressure_notify(zone, pressure);
+}
+
+#endif /* _LINUX_MEM_NOTIFY_H */
Index: b/include/linux/mmzone.h
===================================================================
--- a/include/linux/mmzone.h 2008-02-03 20:59:43.000000000 +0900
+++ b/include/linux/mmzone.h 2008-02-03 20:59:46.000000000 +0900
@@ -283,6 +283,7 @@ struct zone {
*/
int prev_priority;
+ int mem_notify_status;
ZONE_PADDING(_pad2_)
/* Rarely used or read-mostly fields */
Index: b/mm/Makefile
===================================================================
--- a/mm/Makefile 2008-02-03 20:59:43.000000000 +0900
+++ b/mm/Makefile 2008-02-03 20:59:46.000000000 +0900
@@ -11,7 +11,7 @@ obj-y := bootmem.o filemap.o mempool.o
page_alloc.o page-writeback.o pdflush.o \
readahead.o swap.o truncate.o vmscan.o \
prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
- page_isolation.o $(mmu-y)
+ page_isolation.o mem_notify.o $(mmu-y)
obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
obj-$(CONFIG_BOUNCE) += bounce.o
Index: b/mm/mem_notify.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ b/mm/mem_notify.c 2008-02-03 21:02:30.000000000 +0900
@@ -0,0 +1,123 @@
+/*
+ * Notify applications of memory pressure via /dev/mem_notify
+ *
+ * Copyright (C) 2008 Marcelo Tosatti <marcelo@xxxxxxxxx>,
+ * KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
+ *
+ * Released under the GPL, see the file COPYING for details.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/timer.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/vmstat.h>
+#include <linux/percpu.h>
+#include <linux/timer.h>
+#include <linux/mem_notify.h>
+
+#include <asm/atomic.h>
+
+#define MAX_PROC_WAKEUP_GUARD (10*HZ)
+#define MAX_WAKEUP_TASKS (100)
+
+struct mem_notify_file_info {
+ unsigned long last_proc_notify;
+};
+
+static DECLARE_WAIT_QUEUE_HEAD(mem_wait);
+static atomic_long_t nr_under_memory_pressure_zones = ATOMIC_LONG_INIT(0);
+static atomic_t nr_watcher_task = ATOMIC_INIT(0);
+
+atomic_long_t last_mem_notify = ATOMIC_LONG_INIT(INITIAL_JIFFIES);
+
+void __memory_pressure_notify(struct zone *zone, int pressure)
+{
+ int nr_wakeup;
+ int flags;
+
+ spin_lock_irqsave(&mem_wait.lock, flags);
+
+ if (pressure != zone->mem_notify_status) {
+ long val = pressure ? 1 : -1;
+ atomic_long_add(val, &nr_under_memory_pressure_zones);
+ zone->mem_notify_status = pressure;
+ }
+
+ if (pressure) {
+ int nr_watcher = atomic_read(&nr_watcher_task);
+
+ atomic_long_set(&last_mem_notify, jiffies);
+ if (!nr_watcher)
+ goto out;
+
+ nr_wakeup = (nr_watcher >> 4) + 1;
+ if (unlikely(nr_wakeup > MAX_WAKEUP_TASKS))
+ nr_wakeup = MAX_WAKEUP_TASKS;
+
+ wake_up_locked_nr(&mem_wait, nr_wakeup);
+ }
+out:
+ spin_unlock_irqrestore(&mem_wait.lock, flags);
+}
+
+static int mem_notify_open(struct inode *inode, struct file *file)
+{
+ struct mem_notify_file_info *info;
+ int err = 0;
+
+ info = kmalloc(sizeof(*info), GFP_KERNEL);
+ if (!info) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ info->last_proc_notify = INITIAL_JIFFIES;
+ file->private_data = info;
+ atomic_inc(&nr_watcher_task);
+out:
+ return err;
+}
+
+static int mem_notify_release(struct inode *inode, struct file *file)
+{
+ kfree(file->private_data);
+ atomic_dec(&nr_watcher_task);
+ return 0;
+}
+
+static unsigned int mem_notify_poll(struct file *file, poll_table *wait)
+{
+ struct mem_notify_file_info *info = file->private_data;
+ unsigned long now = jiffies;
+ unsigned long timeout;
+ unsigned int retval = 0;
+ unsigned long guard_time;
+
+ poll_wait_exclusive(file, &mem_wait, wait);
+
+ guard_time = min_t(unsigned long,
+ MEM_NOTIFY_FREQ * atomic_read(&nr_watcher_task),
+ MAX_PROC_WAKEUP_GUARD);
+ timeout = info->last_proc_notify + guard_time;
+ if (time_before(now, timeout))
+ goto out;
+
+ if (atomic_long_read(&nr_under_memory_pressure_zones) != 0) {
+ info->last_proc_notify = now;
+ retval = POLLIN;
+ }
+
+out:
+ return retval;
+}
+
+struct file_operations mem_notify_fops = {
+ .open = mem_notify_open,
+ .release = mem_notify_release,
+ .poll = mem_notify_poll,
+};
+EXPORT_SYMBOL(mem_notify_fops);
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c 2008-02-03 20:59:43.000000000 +0900
+++ b/mm/page_alloc.c 2008-02-03 21:01:43.000000000 +0900
@@ -3458,6 +3458,7 @@ static void __meminit free_area_init_cor
zone->zone_pgdat = pgdat;
zone->prev_priority = DEF_PRIORITY;
+ zone->mem_notify_status = 0;
zone_pcp_init(zone);
INIT_LIST_HEAD(&zone->active_list);
Index: b/Documentation/devices.txt
===================================================================
--- a/Documentation/devices.txt 2008-02-03 20:59:43.000000000 +0900
+++ b/Documentation/devices.txt 2008-02-03 20:59:46.000000000 +0900
@@ -96,6 +96,7 @@ Your cooperation is appreciated.
11 = /dev/kmsg Writes to this come out as printk's
12 = /dev/oldmem Used by crashdump kernels to access
the memory of the kernel that crashed.
+ 13 = /dev/mem_notify Low memory notification.
1 block RAM disk
0 = /dev/ram0 First RAM disk
-
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