first try for swap prefetch

diff -urP linux-2.5.67/arch/i386/Kconfig linux-2.5.67_patched/arch/i386/Kconfig
--- linux-2.5.67/arch/i386/Kconfig	Mon Apr  7 19:30:43 2003
+++ linux-2.5.67_patched/arch/i386/Kconfig	Thu Apr 10 17:47:36 2003
@@ -373,6 +373,13 @@
 	depends on MK8 || MPENTIUM4
 	default y
 
+config SWAP_PREFETCH
+	tristate "Prefetch swapped memory"
+	depends on SWAP
+	help
+	  This option enables the kernel to prefetch swapped memory pages
+	  when idle.
+
 config HUGETLB_PAGE
 	bool "Huge TLB Page Support"
 	help
diff -urP linux-2.5.67/include/linux/swap.h linux-2.5.67_patched/include/linux/swap.h
--- linux-2.5.67/include/linux/swap.h	Mon Apr  7 19:30:35 2003
+++ linux-2.5.67_patched/include/linux/swap.h	Thu Apr 10 18:36:33 2003
@@ -155,6 +155,8 @@
 extern unsigned int nr_free_pages_pgdat(pg_data_t *pgdat);
 extern unsigned int nr_free_buffer_pages(void);
 extern unsigned int nr_free_pagecache_pages(void);
+extern unsigned int nr_avail_buffer_pages(void);
+extern unsigned int nr_avail_pagecache_pages(void);
 
 /* linux/mm/swap.c */
 extern void FASTCALL(lru_cache_add(struct page *));
diff -urP linux-2.5.67/include/linux/swap_prefetch.h linux-2.5.67_patched/include/linux/swap_prefetch.h
--- linux-2.5.67/include/linux/swap_prefetch.h	Thu Jan  1 01:00:00 1970
+++ linux-2.5.67_patched/include/linux/swap_prefetch.h	Thu Apr 10 18:36:40 2003
@@ -0,0 +1,52 @@
+#ifndef _LINUX_SWAP_PREFETCH_H
+#define _LINUX_SWAP_PREFETCH_H
+
+#include <linux/swap.h>
+#include <linux/radix-tree.h>
+
+struct swapped_entry_t {
+	struct list_head list;
+	swp_entry_t entry;
+};
+
+struct swapped_root_t {
+	spinlock_t lock;
+	struct list_head list;
+	struct radix_tree_root tree;
+};
+
+extern struct swapped_root_t swapped_root;
+
+static inline void add_to_swapped_list(swp_entry_t entry)
+{
+	struct swapped_entry_t * swapped_entry;
+	int ret;
+
+	swapped_entry = kmalloc(sizeof(*swapped_entry), GFP_ATOMIC);
+	if(swapped_entry) {
+		swapped_entry->entry = entry;
+		spin_lock(&swapped_root.lock);
+		ret = radix_tree_insert(&swapped_root.tree, entry.val, swapped_entry);
+		if(ret == 0)
+			list_add(&swapped_entry->list, &swapped_root.list);
+		else
+			kfree(swapped_entry);
+		spin_unlock(&swapped_root.lock);
+	}
+}
+
+static inline void remove_from_swapped_list(swp_entry_t entry)
+{
+	struct swapped_entry_t * swapped_entry;
+
+	spin_lock(&swapped_root.lock);
+	swapped_entry = radix_tree_lookup(&swapped_root.tree, entry.val);
+	if(swapped_entry) {
+		list_del(&swapped_entry->list);
+		radix_tree_delete(&swapped_root.tree, entry.val);
+		kfree(swapped_entry);
+	}
+	spin_unlock(&swapped_root.lock);
+}
+
+#endif /* _LINUX_SWAP_PREFETCH_H */
diff -urP linux-2.5.67/kernel/ksyms.c linux-2.5.67_patched/kernel/ksyms.c
--- linux-2.5.67/kernel/ksyms.c	Mon Apr  7 19:30:34 2003
+++ linux-2.5.67_patched/kernel/ksyms.c	Thu Apr 10 17:47:36 2003
@@ -58,6 +58,7 @@
 #include <linux/ptrace.h>
 #include <linux/time.h>
 #include <linux/backing-dev.h>
+#include <linux/swap_prefetch.h>
 #include <asm/checksum.h>
 
 #if defined(CONFIG_PROC_FS)
@@ -70,6 +71,11 @@
 extern struct timezone sys_tz;
 
 extern int panic_timeout;
+
+/* needed for swap prefetch support */
+EXPORT_SYMBOL(swapped_root);
+EXPORT_SYMBOL(nr_avail_pagecache_pages);
+EXPORT_SYMBOL(read_swap_cache_async);
 
 /* process memory management */
 EXPORT_SYMBOL(do_mmap_pgoff);
diff -urP linux-2.5.67/mm/Makefile linux-2.5.67_patched/mm/Makefile
--- linux-2.5.67/mm/Makefile	Mon Apr  7 19:31:52 2003
+++ linux-2.5.67_patched/mm/Makefile	Thu Apr 10 17:47:36 2003
@@ -12,3 +12,5 @@
 			   slab.o swap.o truncate.o vcache.o vmscan.o $(mmu-y)
 
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
+
+obj-$(CONFIG_SWAP_PREFETCH)	+= swap_prefetch.o
diff -urP linux-2.5.67/mm/page_alloc.c linux-2.5.67_patched/mm/page_alloc.c
--- linux-2.5.67/mm/page_alloc.c	Mon Apr  7 19:30:39 2003
+++ linux-2.5.67_patched/mm/page_alloc.c	Thu Apr 10 17:47:36 2003
@@ -787,6 +787,48 @@
 }
 #endif
 
+static unsigned int nr_avail_zone_pages(int offset)
+{
+	pg_data_t *pgdat;
+	unsigned long avail = 0;
+
+	for_each_pgdat(pgdat) {
+		struct zonelist *zonelist = pgdat->node_zonelists + offset;
+		struct zone **zonep = zonelist->zones;
+		struct zone *zone;
+		unsigned long low = 0;
+
+		for (zone = *zonep++; zone; zone = *zonep++) {
+			unsigned long local_free = zone->free_pages;
+			unsigned long local_low  = zone->pages_low;
+			
+			low += local_low;
+			if (local_free > low) {
+				avail = max(avail, local_free - low);
+			}
+			low += local_low * sysctl_lower_zone_protection;
+		}
+	}
+
+	return avail;
+}
+
+/*
+ * Amount of available RAM allocatable within ZONE_DMA and ZONE_NORMAL
+ */
+unsigned int nr_avail_buffer_pages(void)
+{
+	return nr_avail_zone_pages(GFP_USER & GFP_ZONEMASK);
+}
+
+/*
+ * Amount of available RAM allocatable within all zones
+ */
+unsigned int nr_avail_pagecache_pages(void)
+{
+	return nr_avail_zone_pages(GFP_HIGHUSER & GFP_ZONEMASK);
+}
+
 #ifdef CONFIG_NUMA
 static void show_node(struct zone *zone)
 {
diff -urP linux-2.5.67/mm/swap_prefetch.c linux-2.5.67_patched/mm/swap_prefetch.c
--- linux-2.5.67/mm/swap_prefetch.c	Thu Jan  1 01:00:00 1970
+++ linux-2.5.67_patched/mm/swap_prefetch.c	Thu Apr 10 18:33:06 2003
@@ -0,0 +1,79 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/swap_prefetch.h>
+
+#define INTERVAL	60		/* (secs) Default is 1 minute */
+
+static int interval       = INTERVAL;
+
+MODULE_PARM(interval,"i");
+MODULE_PARM_DESC(interval,
+	"delay in seconds to wait between memory checks (default 60)");
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Thomas Schlichter <thomas.schlichter@web.de>");
+MODULE_DESCRIPTION("prefetches swap pages when there is free memory");
+
+/*
+ *	Our timer
+ */
+static void prefetch_timer_handler(unsigned long data);
+static struct timer_list prefetch_timer =
+		TIMER_INITIALIZER(prefetch_timer_handler, 0, 0);
+
+/*
+ *	Our work
+ */
+static void prefetch_work_handler(void *data);
+static DECLARE_WORK(prefetch_work, prefetch_work_handler, 0);
+
+/*
+ *	If the timer expires..
+ */
+static void prefetch_timer_handler(unsigned long data)
+{
+	schedule_work(&prefetch_work);
+	prefetch_timer.expires = jiffies + interval * HZ;
+	add_timer(&prefetch_timer);
+}
+
+/*
+ *	..do the work
+ */
+static void prefetch_work_handler(void *data)
+{
+	printk(KERN_INFO "Available pages before: %d\n", nr_avail_pagecache_pages());
+
+	while(nr_avail_pagecache_pages() != 0) {
+		struct swapped_entry_t *swapped_entry;
+		swp_entry_t entry;
+
+		spin_lock(&swapped_root.lock);
+		if(list_empty(&swapped_root.list)) {
+			spin_unlock(&swapped_root.lock);
+			break;
+		}
+		swapped_entry = list_entry(swapped_root.list.next,
+					struct swapped_entry_t, list);
+		entry = swapped_entry->entry;
+		spin_unlock(&swapped_root.lock);
+
+		read_swap_cache_async(entry);
+	}
+
+	printk(KERN_INFO "Available pages after: %d\n", nr_avail_pagecache_pages());
+}
+
+static int __init prefetch_init(void)
+{
+	prefetch_timer_handler(0);
+	return 0;
+}
+
+static void __exit prefetch_exit(void)
+{
+	del_timer(&prefetch_timer);
+}
+
+module_init(prefetch_init);
+module_exit(prefetch_exit);
diff -urP linux-2.5.67/mm/swap_state.c linux-2.5.67_patched/mm/swap_state.c
--- linux-2.5.67/mm/swap_state.c	Mon Apr  7 19:31:11 2003
+++ linux-2.5.67_patched/mm/swap_state.c	Thu Apr 10 18:32:32 2003
@@ -14,6 +14,7 @@
 #include <linux/pagemap.h>
 #include <linux/backing-dev.h>
 #include <linux/buffer_head.h>	/* block_sync_page() */
+#include <linux/swap_prefetch.h>
 
 #include <asm/pgtable.h>
 
@@ -49,6 +50,12 @@
 	.private_list	= LIST_HEAD_INIT(swapper_space.private_list),
 };
 
+struct swapped_root_t swapped_root = {
+	.lock = SPIN_LOCK_UNLOCKED,
+	.list = LIST_HEAD_INIT(swapped_root.list),
+	.tree = RADIX_TREE_INIT(GFP_ATOMIC),
+};
+
 #define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
 
 static struct {
@@ -344,6 +351,8 @@
 {
 	struct page *found_page, *new_page = NULL;
 	int err;
+
+	remove_from_swapped_list(entry);
 
 	do {
 		/*
diff -urP linux-2.5.67/mm/vmscan.c linux-2.5.67_patched/mm/vmscan.c
--- linux-2.5.67/mm/vmscan.c	Mon Apr  7 19:30:43 2003
+++ linux-2.5.67_patched/mm/vmscan.c	Thu Apr 10 18:31:02 2003
@@ -27,6 +27,7 @@
 #include <linux/pagevec.h>
 #include <linux/backing-dev.h>
 #include <linux/rmap-locking.h>
+#include <linux/swap_prefetch.h>
 
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
@@ -402,6 +403,7 @@
 			swp_entry_t swap = { .val = page->index };
 			__delete_from_swap_cache(page);
 			write_unlock(&mapping->page_lock);
+			add_to_swapped_list(swap);
 			swap_free(swap);
 			__put_page(page);	/* The pagecache ref */
 			goto free_it;