Hi,

This is a brush up of the refault patches, as presented by Rik at last
year's OLS:

  http://people.redhat.com/riel/riel-OLS2006.pdf

When talking to people at OLS this year there was a renewed interrest in
the concept.


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From: Rik van Riel <riel@redhat.com>

Track non-resident pages through a simple hashing scheme.  This way
the space overhead is limited to 1 u32 per page, or 0.1% space overhead
and lookups are one cache miss.

Aside from seeing whether or not a page was recently evicted, we can
also take a reasonable guess at how many other pages were evicted since
this page was evicted.

TODO: make the entries unsigned long, currently we're limited to 
1^32*NUM_NR*PAGE_SIZE bytes of memory. Event though this would end up
being 1008 TB of memory, I suspect the hash function to go crap at around
4 to 16 TB.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 Documentation/kernel-parameters.txt |    4 
 include/linux/nonresident.h         |   35 +++++++
 init/main.c                         |    2 
 mm/Kconfig                          |    4 
 mm/Makefile                         |    1 
 mm/nonresident.c                    |  173 ++++++++++++++++++++++++++++++++++++
 mm/swap.c                           |    3 
 mm/vmscan.c                         |    3 
 8 files changed, 225 insertions(+)

Index: linux-2.6/mm/nonresident.c
===================================================================
--- /dev/null
+++ linux-2.6/mm/nonresident.c
@@ -0,0 +1,173 @@
+/*
+ * mm/nonresident.c
+ * (C) 2004,2005 Red Hat, Inc
+ * Written by Rik van Riel <riel@redhat.com>
+ * Released under the GPL, see the file COPYING for details.
+ *
+ * Keeps track of whether a non-resident page was recently evicted
+ * and should be immediately promoted to the active list. This also
+ * helps automatically tune the inactive target.
+ *
+ * The pageout code stores a recently evicted page in this cache
+ * by calling remember_page(mapping/mm, index/vaddr, generation)
+ * and can look it up in the cache by calling recently_evicted()
+ * with the same arguments.
+ *
+ * Note that there is no way to invalidate pages after eg. truncate
+ * or exit, we let the pages fall out of the non-resident set through
+ * normal replacement.
+ */
+#include <linux/mm.h>
+#include <linux/cache.h>
+#include <linux/spinlock.h>
+#include <linux/bootmem.h>
+#include <linux/hash.h>
+#include <linux/prefetch.h>
+#include <linux/kernel.h>
+
+/* Number of non-resident pages per hash bucket. Never smaller than 15. */
+#if (L1_CACHE_BYTES < 64)
+#define NR_BUCKET_BYTES 64
+#else
+#define NR_BUCKET_BYTES L1_CACHE_BYTES
+#endif
+#define NUM_NR ((NR_BUCKET_BYTES - sizeof(atomic_t))/sizeof(atomic_t))
+
+struct nr_bucket
+{
+	atomic_t hand;
+	atomic_t cookie[NUM_NR];
+} ____cacheline_aligned;
+
+/* The non-resident page hash table. */
+static struct nr_bucket *nonres_table;
+static unsigned int nonres_shift;
+static unsigned int nonres_mask;
+
+static struct nr_bucket *nr_hash(void *mapping, unsigned long index)
+{
+	unsigned long bucket;
+	unsigned long hash;
+
+	hash = hash_ptr(mapping, BITS_PER_LONG);
+	hash = 37 * hash + hash_long(index, BITS_PER_LONG);
+	bucket = hash & nonres_mask;
+
+	return nonres_table + bucket;
+}
+
+static u32 nr_cookie(struct address_space *mapping, unsigned long index)
+{
+	unsigned long cookie;
+
+	cookie = hash_ptr(mapping, BITS_PER_LONG);
+	cookie = 37 * cookie + hash_long(index, BITS_PER_LONG);
+
+	if (mapping && mapping->host) {
+		cookie *= 37;
+		cookie += hash_long(mapping->host->i_ino, BITS_PER_LONG);
+	}
+
+	return (u32)(cookie >> (BITS_PER_LONG - 32));
+}
+
+unsigned long
+nonresident_get(struct address_space *mapping, unsigned long index)
+{
+	struct nr_bucket *bucket;
+	unsigned long distance = ~0UL;
+	u32 wanted;
+	int i;
+
+	if (!mapping)
+		return distance;
+
+	prefetch(mapping->host);
+	bucket = nr_hash(mapping, index);
+
+	prefetch(bucket);
+	wanted = nr_cookie(mapping, index);
+
+	for (i = 0; i < NUM_NR; i++) {
+		if ((u32)atomic_cmpxchg(&bucket->cookie[i], wanted, 0) == wanted) {
+			/* Return the distance between entry and clock hand. */
+			distance = atomic_read(&bucket->hand) + NUM_NR - i;
+			distance %= NUM_NR;
+			distance += (bucket - nonres_table);
+			goto out;
+		}
+	}
+
+out:
+	return distance;
+}
+
+u32 nonresident_put(struct address_space *mapping, unsigned long index)
+{
+	struct nr_bucket *bucket;
+	u32 cookie;
+	int cur_hand;
+	int hand;
+
+	prefetch(mapping->host);
+	bucket = nr_hash(mapping, index);
+
+	prefetchw(bucket);
+	cookie = nr_cookie(mapping, index);
+
+	/* Atomically find the next array index. */
+	do {
+		cur_hand = atomic_read(&bucket->hand);
+		hand = cur_hand + 1;
+		if (unlikely(hand == NUM_NR))
+			hand = 0;
+	} while (atomic_cmpxchg(&bucket->hand, cur_hand, hand) != cur_hand);
+
+	/* Statistics may want to know whether the entry was in use. */
+	return atomic_xchg(&bucket->cookie[hand], cookie);
+}
+
+unsigned long nonresident_total(void)
+{
+	return NUM_NR << nonres_shift;
+}
+
+/*
+ * For interactive workloads, we remember about as many non-resident pages
+ * as we have actual memory pages.  For server workloads with large inter-
+ * reference distances we could benefit from remembering more.
+ */
+static __initdata unsigned long nonresident_factor = 100;
+void __init nonresident_init(void)
+{
+	int target;
+	int i;
+
+	/*
+	 * Calculate the non-resident hash bucket target. Use a power of
+	 * two for the division because alloc_large_system_hash rounds up.
+	 */
+	target = (nr_all_pages * nonresident_factor) / 100;
+	target /= (sizeof(struct nr_bucket) / sizeof(atomic_t));
+
+	nonres_table = alloc_large_system_hash("Non-resident page tracking",
+					sizeof(struct nr_bucket),
+					target,
+					0,
+					HASH_EARLY,
+					&nonres_shift,
+					&nonres_mask,
+					0);
+
+	for (i = 0; i < (1 << nonres_shift); i++)
+		atomic_set(&nonres_table[i].hand, 0);
+}
+
+static int __init set_nonresident_factor(char *str)
+{
+	if (!str)
+		return 0;
+	nonresident_factor = simple_strtoul(str, &str, 0);
+	return 1;
+}
+__setup("nonresident_factor=", set_nonresident_factor);
Index: linux-2.6/include/linux/nonresident.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/nonresident.h
@@ -0,0 +1,35 @@
+#ifndef _LINUX_NONRESIDENT_H_
+#define _LINUX_NONRESIDENT_H_
+
+#ifdef __KERNEL__
+
+#ifdef CONFIG_MM_NONRESIDENT
+
+extern void nonresident_init(void);
+extern unsigned long nonresident_get(struct address_space *, unsigned long);
+extern u32 nonresident_put(struct address_space *, unsigned long);
+extern unsigned long nonresident_total(void);
+
+#else /* CONFIG_MM_NONRESIDENT */
+
+static inline void nonresident_init(void) { }
+static inline
+unsigned long nonresident_get(struct address_space *, unsigned long, int)
+{
+	return 0;
+}
+
+static inline u32 nonresident_put(struct address_space *, unsigned long)
+{
+	return 0;
+}
+
+static inline unsigned long nonresident_total(void)
+{
+	return 0;
+}
+
+#endif /* CONFIG_MM_NONRESIDENT */
+
+#endif /* __KERNEL */
+#endif /* _LINUX_NONRESIDENT_H_ */
Index: linux-2.6/init/main.c
===================================================================
--- linux-2.6.orig/init/main.c
+++ linux-2.6/init/main.c
@@ -55,6 +55,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/device.h>
 #include <linux/kthread.h>
+#include <linux/nonresident.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -611,6 +612,7 @@ asmlinkage void __init start_kernel(void
 #endif
 	vfs_caches_init_early();
 	cpuset_init_early();
+	nonresident_init();
 	mem_init();
 	kmem_cache_init();
 	setup_per_cpu_pageset();
Index: linux-2.6/mm/Makefile
===================================================================
--- linux-2.6.orig/mm/Makefile
+++ linux-2.6/mm/Makefile
@@ -15,6 +15,7 @@ obj-y			:= bootmem.o filemap.o mempool.o
 
 obj-$(CONFIG_BOUNCE)	+= bounce.o
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o thrash.o
+obj-$(CONFIG_MM_NONRESIDENT) += nonresident.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o
 obj-$(CONFIG_SPARSEMEM)	+= sparse.o
Index: linux-2.6/mm/swap.c
===================================================================
--- linux-2.6.orig/mm/swap.c
+++ linux-2.6/mm/swap.c
@@ -30,6 +30,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/init.h>
+#include <linux/nonresident.h>
 
 /* How many pages do we try to swap or page in/out together? */
 int page_cluster;
@@ -365,6 +366,7 @@ void __pagevec_lru_add(struct pagevec *p
 		}
 		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
+		nonresident_get(page_mapping(page), page_index(page));
 		add_page_to_inactive_list(zone, page);
 	}
 	if (zone)
@@ -392,6 +394,7 @@ void __pagevec_lru_add_active(struct pag
 		}
 		VM_BUG_ON(PageLRU(page));
 		SetPageLRU(page);
+		nonresident_get(page_mapping(page), page_index(page));
 		VM_BUG_ON(PageActive(page));
 		SetPageActive(page);
 		add_page_to_active_list(zone, page);
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -37,6 +37,7 @@
 #include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/nonresident.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -402,6 +403,7 @@ int remove_mapping(struct address_space 
 
 	if (PageSwapCache(page)) {
 		swp_entry_t swap = { .val = page_private(page) };
+		nonresident_put(mapping, page_index(page));
 		__delete_from_swap_cache(page);
 		write_unlock_irq(&mapping->tree_lock);
 		swap_free(swap);
@@ -409,6 +411,7 @@ int remove_mapping(struct address_space 
 		return 1;
 	}
 
+	nonresident_put(mapping, page_index(page));
 	__remove_from_page_cache(page);
 	write_unlock_irq(&mapping->tree_lock);
 	__put_page(page);
Index: linux-2.6/mm/Kconfig
=========================

Adds a refault histogram for those policies that use nonresident page tracking.
Based on ideas and code from Rik van Riel.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/nonresident.h |   12 +++
 mm/Kconfig                  |    5 +
 mm/Makefile                 |    1 
 mm/nonresident.c            |    2 
 mm/refault.c                |  143 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 163 insertions(+)

Index: linux-2.6/mm/Kconfig
===================================================================
--- linux-2.6.orig/mm/Kconfig
+++ linux-2.6/mm/Kconfig
@@ -162,6 +162,11 @@ config MM_NONRESIDENT
 	bool "Track nonresident pages"
 	def_bool y
 
+config MM_REFAULT
+	bool "Refault histogram"
+	def_bool y
+	depends on MM_NONRESIDENT
+
 config ZONE_DMA_FLAG
 	int
 	default "0" if !ZONE_DMA
Index: linux-2.6/mm/nonresident.c
===================================================================
--- linux-2.6.orig/mm/nonresident.c
+++ linux-2.6/mm/nonresident.c
@@ -24,6 +24,7 @@
 #include <linux/hash.h>
 #include <linux/prefetch.h>
 #include <linux/kernel.h>
+#include <linux/nonresident.h>
 
 /* Number of non-resident pages per hash bucket. Never smaller than 15. */
 #if (L1_CACHE_BYTES < 64)
@@ -99,6 +100,7 @@ nonresident_get(struct address_space *ma
 	}
 
 out:
+	nonresident_refault(distance);
 	return distance;
 }
 
Index: linux-2.6/mm/refault.c
===================================================================
--- /dev/null
+++ linux-2.6/mm/refault.c
@@ -0,0 +1,143 @@
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
+#include <linux/nonresident.h>
+#include <linux/uaccess.h>
+
+#define BUCKETS 16
+
+DEFINE_PER_CPU(unsigned long[BUCKETS+1], refault_histogram);
+
+void nonresident_refault(unsigned long distance)
+{
+	unsigned long nonres_bucket = nonresident_total() / BUCKETS;
+	unsigned long bucket_id = distance / nonres_bucket;
+
+	if (bucket_id > BUCKETS)
+		bucket_id = BUCKETS;
+
+	__get_cpu_var(refault_histogram)[bucket_id]++;
+}
+
+#ifdef CONFIG_PROC_FS
+
+#include <linux/seq_file.h>
+
+static void *frag_start(struct seq_file *m, loff_t *pos)
+{
+	if (*pos < 0 || *pos > BUCKETS)
+		return NULL;
+
+	m->private = (void *)(unsigned long)*pos;
+
+	return pos;
+}
+
+static void *frag_next(struct seq_file *m, void *arg, loff_t *pos)
+{
+	if (*pos < BUCKETS) {
+		(*pos)++;
+		(*((unsigned long *)&m->private))++;
+		return pos;
+	}
+	return NULL;
+}
+
+static void frag_stop(struct seq_file *m, void *arg)
+{
+}
+
+unsigned long get_refault_stat(unsigned long index)
+{
+	unsigned long total = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		total += per_cpu(refault_histogram, cpu)[index];
+
+	return total;
+}
+
+#define K(pages)	(pages << (PAGE_SHIFT - 10))
+
+static int frag_show(struct seq_file *m, void *arg)
+{
+	unsigned long index = (unsigned long)m->private;
+	unsigned long nonres_bucket = nonresident_total() / BUCKETS;
+	unsigned long upper = ((unsigned long)index + 1) * nonres_bucket;
+	unsigned long lower = (unsigned long)index * nonres_bucket;
+	unsigned long hits = get_refault_stat(index);
+
+	if (index == 0)
+		seq_printf(m, "     Refault distance          Hits\n");
+
+	if (index < BUCKETS)
+		seq_printf(m, "%9luK - %9luK     %9lu\n", K(lower), K(upper), hits);
+	else
+		seq_printf(m, " New/Beyond %9luK     %9lu\n", K(lower), hits);
+
+	return 0;
+}
+
+struct seq_operations refault_op = {
+	.start  = frag_start,
+	.next   = frag_next,
+	.stop   = frag_stop,
+	.show   = frag_show,
+};
+
+static void refault_reset(void)
+{
+	int cpu;
+	int bucket_id;
+
+	for_each_possible_cpu(cpu) {
+		for (bucket_id = 0; bucket_id <= BUCKETS; ++bucket_id)
+			per_cpu(refault_histogram, cpu)[bucket_id] = 0;
+	}
+}
+
+ssize_t refault_write(struct file *file, const char __user *buf,
+		      size_t count, loff_t *ppos)
+{
+	if (count) {
+		char c;
+
+		if (get_user(c, buf))
+			return -EFAULT;
+		if (c == '0')
+			refault_reset();
+	}
+	return count;
+}
+
+static int refault_open(struct inode *inode, struct file *file)
+{
+       (void)inode;
+       return seq_open(file, &refault_op);
+}
+
+static struct file_operations refault_file_operations = {
+       .open           = refault_open,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = seq_release,
+       .write          = refault_write,
+};
+
+static int __init refault_proc_init(void)
+{
+	struct proc_dir_entry *entry;
+
+	entry = create_proc_entry("refault", S_IRUSR, NULL);
+	if (entry)
+		entry->proc_fops = &refault_file_operations;
+
+	return 0;
+}
+
+__initcall(refault_proc_init);
+
+#endif /* CONFIG_PROCFS */
+
Index: linux-2.6/mm/Makefile
===================================================================
--- linux-2.6.orig/mm/Makefile
+++ linux-2.6/mm/Makefile
@@ -16,6 +16,7 @@ obj-y			:= bootmem.o filemap.o mempool.o
 obj-$(CONFIG_BOUNCE)	+= bounce.o
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o thrash.o
 obj-$(CONFIG_MM_NONRESIDENT) += nonresident.o
+obj-$(CONFIG_MM_REFAULT) += refault.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o
 obj-$(CONFIG_SPARSEMEM)	+= sparse.o
Index: linux-2.6/include/linux/nonresident.h
===================================================================
--- linux-2.6.orig/include/linux/nonresident.h
+++ linux-2.6/include/linux/nonresident.h
@@ -31,5 +31,17 @@ static inline unsigned long nonresident_
 
 #endif /* CONFIG_MM_NONRESIDENT */
 
+#ifdef CONFIG_MM_REFAULT
+
+extern void nonresident_refault(unsigned long);
+
+#else
+
+static inline void nonresident_refault(unsigned long distance)
+{
+}
+
+#endif
+
 #endif /* __KERNEL */
 #endif /* _LINUX_NONRESIDENT_H_ */

-- 

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