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Hi,
as mentioned a few days ago I was going to try to implement a swap prefetch=
to=20
better utilize the free memory. Now here is my first try. This version work=
s=20
only as a module and tests for free pagecahe memory in a interval specified=
=20
as a module parameter.
As I tested this I saw that many of the page reloads do not come from the s=
wap=20
space but from buffers that got moved away. I could easily save which buffe=
rs=20
have been removed but I don't know how to read them back to the pagecache...
An other thing I saw was that anywhere in the kernel there must be some cod=
e=20
which always tries to hold some memory pages free, even if there are cached=
=20
pages that just can be freed as they are not modified... Perhaps that code=
=20
should be changed...
I hope someone may give me some hints or show me obvious mistakes I made...=
=20
;-)
Thank you!
Best regards
Thomas
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diff -urP linux-2.5.67/arch/i386/Kconfig linux-2.5.67_patched/arch/i386/Kco=
nfig
=2D-- 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
=20
+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/li=
nux/swap.h
=2D-- 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);
=20
/* 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/i=
nclude/linux/swap_prefetch.h
=2D-- 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 =3D kmalloc(sizeof(*swapped_entry), GFP_ATOMIC);
+ if(swapped_entry) {
+ swapped_entry->entry =3D entry;
+ spin_lock(&swapped_root.lock);
+ ret =3D radix_tree_insert(&swapped_root.tree, entry.val, swapped_entry);
+ if(ret =3D=3D 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 =3D 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
=2D-- 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>
=20
#if defined(CONFIG_PROC_FS)
@@ -70,6 +71,11 @@
extern struct timezone sys_tz;
=20
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);
=20
/* process memory management */
EXPORT_SYMBOL(do_mmap_pgoff);
diff -urP linux-2.5.67/mm/Makefile linux-2.5.67_patched/mm/Makefile
=2D-- 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 $(mmu-y)
=20
obj-$(CONFIG_SWAP) +=3D page_io.o swap_state.o swapfile.o
+
+obj-$(CONFIG_SWAP_PREFETCH) +=3D swap_prefetch.o
diff -urP linux-2.5.67/mm/page_alloc.c linux-2.5.67_patched/mm/page_alloc.c
=2D-- 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
=20
+static unsigned int nr_avail_zone_pages(int offset)
+{
+ pg_data_t *pgdat;
+ unsigned long avail =3D 0;
+
+ for_each_pgdat(pgdat) {
+ struct zonelist *zonelist =3D pgdat->node_zonelists + offset;
+ struct zone **zonep =3D zonelist->zones;
+ struct zone *zone;
+ unsigned long low =3D 0;
+
+ for (zone =3D *zonep++; zone; zone =3D *zonep++) {
+ unsigned long local_free =3D zone->free_pages;
+ unsigned long local_low =3D zone->pages_low;
+ =09
+ low +=3D local_low;
+ if (local_free > low) {
+ avail =3D max(avail, local_free - low);
+ }
+ low +=3D 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_pref=
etch.c
=2D-- 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 =3D 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 =3D
+ 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 =3D 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() !=3D 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 =3D list_entry(swapped_root.list.next,
+ struct swapped_entry_t, list);
+ entry =3D 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
=2D-- 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>
=20
#include <asm/pgtable.h>
=20
@@ -49,6 +50,12 @@
.private_list =3D LIST_HEAD_INIT(swapper_space.private_list),
};
=20
+struct swapped_root_t swapped_root =3D {
+ .lock =3D SPIN_LOCK_UNLOCKED,
+ .list =3D LIST_HEAD_INIT(swapped_root.list),
+ .tree =3D RADIX_TREE_INIT(GFP_ATOMIC),
+};
+
#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
=20
static struct {
@@ -344,6 +351,8 @@
{
struct page *found_page, *new_page =3D NULL;
int err;
+
+ remove_from_swapped_list(entry);
=20
do {
/*
diff -urP linux-2.5.67/mm/vmscan.c linux-2.5.67_patched/mm/vmscan.c
=2D-- 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>
=20
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
@@ -402,6 +403,7 @@
swp_entry_t swap =3D { .val =3D 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;
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