From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: [PATCH V6 2/4] mm: frontswap: core code
This second patch of four in this frontswap series provides the core code
for frontswap that interfaces between the hooks in the swap subsystem and
a frontswap backend via frontswap_ops.
Two new files are added: mm/frontswap.c and include/linux/frontswap.h
Credits: Frontswap_ops design derived from Jeremy Fitzhardinge
design for tmem; sysfs code modelled after mm/ksm.c
[v6: rebase to 3.1-rc1]
[v6: lliubbo@xxxxxxxxx: fix null pointer deref if vzalloc fails]
[v6: konrad.wilk@xxxxxxxxx: various checks and code clarifications/comments]
[v5: no change from v4]
[v4: rebase to 2.6.39]
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Reviewed-by: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Acked-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Matthew Wilcox <matthew@xxxxxx>
Cc: Chris Mason <chris.mason@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxxxx>
Cc: Rik Riel <riel@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
--- linux/include/linux/frontswap.h 1969-12-31 17:00:00.000000000 -0700
+++ frontswap/include/linux/frontswap.h 2011-08-08 08:59:08.842693887 -0600
@@ -0,0 +1,92 @@
+#ifndef _LINUX_FRONTSWAP_H
+#define _LINUX_FRONTSWAP_H
+
+#include <linux/swap.h>
+#include <linux/mm.h>
+
+struct frontswap_ops {
+ void (*init)(unsigned);
+ int (*put_page)(unsigned, pgoff_t, struct page *);
+ int (*get_page)(unsigned, pgoff_t, struct page *);
+ void (*flush_page)(unsigned, pgoff_t);
+ void (*flush_area)(unsigned);
+};
+
+extern int frontswap_enabled;
+extern struct frontswap_ops
+ frontswap_register_ops(struct frontswap_ops *ops);
+extern void frontswap_shrink(unsigned long);
+extern unsigned long frontswap_curr_pages(void);
+
+extern void __frontswap_init(unsigned type);
+extern int __frontswap_put_page(struct page *page);
+extern int __frontswap_get_page(struct page *page);
+extern void __frontswap_flush_page(unsigned, pgoff_t);
+extern void __frontswap_flush_area(unsigned);
+
+#ifndef CONFIG_FRONTSWAP
+/* all inline routines become no-ops and all externs are ignored */
+#define frontswap_enabled (0)
+#endif
+
+static inline int frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+ int ret = 0;
+
+ if (frontswap_enabled && sis->frontswap_map)
+ ret = test_bit(offset % BITS_PER_LONG,
+ &sis->frontswap_map[offset/BITS_PER_LONG]);
+ return ret;
+}
+
+static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
+{
+ if (frontswap_enabled && sis->frontswap_map)
+ set_bit(offset % BITS_PER_LONG,
+ &sis->frontswap_map[offset/BITS_PER_LONG]);
+}
+
+static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+{
+ if (frontswap_enabled && sis->frontswap_map)
+ clear_bit(offset % BITS_PER_LONG,
+ &sis->frontswap_map[offset/BITS_PER_LONG]);
+}
+
+static inline int frontswap_put_page(struct page *page)
+{
+ int ret = -1;
+
+ if (frontswap_enabled)
+ ret = __frontswap_put_page(page);
+ return ret;
+}
+
+static inline int frontswap_get_page(struct page *page)
+{
+ int ret = -1;
+
+ if (frontswap_enabled)
+ ret = __frontswap_get_page(page);
+ return ret;
+}
+
+static inline void frontswap_flush_page(unsigned type, pgoff_t offset)
+{
+ if (frontswap_enabled)
+ __frontswap_flush_page(type, offset);
+}
+
+static inline void frontswap_flush_area(unsigned type)
+{
+ if (frontswap_enabled)
+ __frontswap_flush_area(type);
+}
+
+static inline void frontswap_init(unsigned type)
+{
+ if (frontswap_enabled)
+ __frontswap_init(type);
+}
+
+#endif /* _LINUX_FRONTSWAP_H */
--- linux/mm/frontswap.c 1969-12-31 17:00:00.000000000 -0700
+++ frontswap/mm/frontswap.c 2011-08-08 10:27:42.676687669 -0600
@@ -0,0 +1,346 @@
+/*
+ * Frontswap frontend
+ *
+ * This code provides the generic "frontend" layer to call a matching
+ * "backend" driver implementation of frontswap. See
+ * Documentation/vm/frontswap.txt for more information.
+ *
+ * Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
+ * Author: Dan Magenheimer
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/sysctl.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/proc_fs.h>
+#include <linux/security.h>
+#include <linux/capability.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
+
+/*
+ * frontswap_ops is set by frontswap_register_ops to contain the pointers
+ * to the frontswap "backend" implementation functions.
+ */
+static struct frontswap_ops frontswap_ops;
+
+/*
+ * This global enablement flag reduces overhead on systems where frontswap_ops
+ * has not been registered, so is preferred to the slower alternative: a
+ * function call that checks a non-global.
+ */
+int frontswap_enabled;
+EXPORT_SYMBOL(frontswap_enabled);
+
+/* useful stats available in /sys/kernel/mm/frontswap */
+static unsigned long frontswap_gets;
+static unsigned long frontswap_succ_puts;
+static unsigned long frontswap_failed_puts;
+static unsigned long frontswap_flushes;
+
+/*
+ * register operations for frontswap, returning previous thus allowing
+ * detection of multiple backends and possible nesting
+ */
+struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
+{
+ struct frontswap_ops old = frontswap_ops;
+
+ frontswap_ops = *ops;
+ frontswap_enabled = 1;
+ return old;
+}
+EXPORT_SYMBOL(frontswap_register_ops);
+
+/* Called when a swap device is swapon'd */
+void __frontswap_init(unsigned type)
+{
+ struct swap_info_struct *sis = swap_info[type];
+
+ BUG_ON(sis == NULL);
+ if (sis->frontswap_map == NULL)
+ return;
+ if (frontswap_enabled)
+ (*frontswap_ops.init)(type);
+}
+EXPORT_SYMBOL(__frontswap_init);
+
+/*
+ * "Put" data from a page to frontswap and associate it with the page's
+ * swaptype and offset. Page must be locked and in the swap cache.
+ * If frontswap already contains a page with matching swaptype and
+ * offset, the frontswap implmentation may either overwrite the data
+ * and return success or flush the page from frontswap and return failure
+ */
+int __frontswap_put_page(struct page *page)
+{
+ int ret = -1, dup = 0;
+ swp_entry_t entry = { .val = page_private(page), };
+ int type = swp_type(entry);
+ struct swap_info_struct *sis = swap_info[type];
+ pgoff_t offset = swp_offset(entry);
+
+ BUG_ON(!PageLocked(page));
+ BUG_ON(sis == NULL);
+ if (frontswap_test(sis, offset))
+ dup = 1;
+ ret = (*frontswap_ops.put_page)(type, offset, page);
+ if (ret == 0) {
+ frontswap_set(sis, offset);
+ frontswap_succ_puts++;
+ if (!dup)
+ sis->frontswap_pages++;
+ } else if (dup) {
+ /*
+ failed dup always results in automatic flush of
+ the (older) page from frontswap
+ */
+ frontswap_clear(sis, offset);
+ sis->frontswap_pages--;
+ frontswap_failed_puts++;
+ } else
+ frontswap_failed_puts++;
+ return ret;
+}
+EXPORT_SYMBOL(__frontswap_put_page);
+
+/*
+ * "Get" data from frontswap associated with swaptype and offset that were
+ * specified when the data was put to frontswap and use it to fill the
+ * specified page with data. Page must be locked and in the swap cache
+ */
+int __frontswap_get_page(struct page *page)
+{
+ int ret = -1;
+ swp_entry_t entry = { .val = page_private(page), };
+ int type = swp_type(entry);
+ struct swap_info_struct *sis = swap_info[type];
+ pgoff_t offset = swp_offset(entry);
+
+ BUG_ON(!PageLocked(page));
+ BUG_ON(sis == NULL);
+ if (frontswap_test(sis, offset))
+ ret = (*frontswap_ops.get_page)(type, offset, page);
+ if (ret == 0)
+ frontswap_gets++;
+ return ret;
+}
+EXPORT_SYMBOL(__frontswap_get_page);
+
+/*
+ * Flush any data from frontswap associated with the specified swaptype
+ * and offset so that a subsequent "get" will fail.
+ */
+void __frontswap_flush_page(unsigned type, pgoff_t offset)
+{
+ struct swap_info_struct *sis = swap_info[type];
+
+ BUG_ON(sis == NULL);
+ if (frontswap_test(sis, offset)) {
+ (*frontswap_ops.flush_page)(type, offset);
+ sis->frontswap_pages--;
+ frontswap_clear(sis, offset);
+ frontswap_flushes++;
+ }
+}
+EXPORT_SYMBOL(__frontswap_flush_page);
+
+/*
+ * Flush all data from frontswap associated with all offsets for the
+ * specified swaptype.
+ */
+void __frontswap_flush_area(unsigned type)
+{
+ struct swap_info_struct *sis = swap_info[type];
+
+ BUG_ON(sis == NULL);
+ if (sis->frontswap_map == NULL)
+ return;
+ (*frontswap_ops.flush_area)(type);
+ sis->frontswap_pages = 0;
+ memset(sis->frontswap_map, 0, sis->max / sizeof(long));
+}
+EXPORT_SYMBOL(__frontswap_flush_area);
+
+/*
+ * Frontswap, like a true swap device, may unnecessarily retain pages
+ * under certain circumstances; "shrink" frontswap is essentially a
+ * "partial swapoff" and works by calling try_to_unuse to attempt to
+ * unuse enough frontswap pages to attempt to -- subject to memory
+ * constraints -- reduce the number of pages in frontswap
+ */
+void frontswap_shrink(unsigned long target_pages)
+{
+ int wrapped = 0;
+ bool locked = false;
+
+ /* try a few times to maximize chance of try_to_unuse success */
+ for (wrapped = 0; wrapped < 3; wrapped++) {
+
+ struct swap_info_struct *si = NULL;
+ unsigned long total_pages = 0, total_pages_to_unuse;
+ unsigned long pages = 0, pages_to_unuse = 0;
+ int type;
+
+ /*
+ * we don't want to hold swap_lock while doing a very
+ * lengthy try_to_unuse, but swap_list may change
+ * so restart scan from swap_list.head each time
+ */
+ spin_lock(&swap_lock);
+ locked = true;
+ total_pages = 0;
+ for (type = swap_list.head; type >= 0; type = si->next) {
+ si = swap_info[type];
+ total_pages += si->frontswap_pages;
+ }
+ if (total_pages <= target_pages)
+ goto out;
+ total_pages_to_unuse = total_pages - target_pages;
+ for (type = swap_list.head; type >= 0; type = si->next) {
+ si = swap_info[type];
+ if (total_pages_to_unuse < si->frontswap_pages)
+ pages = pages_to_unuse = total_pages_to_unuse;
+ else {
+ pages = si->frontswap_pages;
+ pages_to_unuse = 0; /* unuse all */
+ }
+ if (security_vm_enough_memory_kern(pages))
+ continue;
+ vm_unacct_memory(pages);
+ break;
+ }
+ if (type < 0)
+ goto out;
+ locked = false;
+ spin_unlock(&swap_lock);
+ try_to_unuse(type, true, pages_to_unuse);
+ }
+
+out:
+ if (locked)
+ spin_unlock(&swap_lock);
+ return;
+}
+EXPORT_SYMBOL(frontswap_shrink);
+
+/*
+ * count and return the number of pages frontswap pages across all
+ * swap devices. This is exported so that a kernel module can
+ * determine current usage without reading sysfs.
+ */
+unsigned long frontswap_curr_pages(void)
+{
+ int type;
+ unsigned long totalpages = 0;
+ struct swap_info_struct *si = NULL;
+
+ spin_lock(&swap_lock);
+ for (type = swap_list.head; type >= 0; type = si->next) {
+ si = swap_info[type];
+ if (si != NULL)
+ totalpages += si->frontswap_pages;
+ }
+ spin_unlock(&swap_lock);
+ return totalpages;
+}
+EXPORT_SYMBOL(frontswap_curr_pages);
+
+#ifdef CONFIG_SYSFS
+
+/* see Documentation/ABI/xxx/sysfs-kernel-mm-frontswap */
+
+#define FRONTSWAP_ATTR_RO(_name) \
+ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+#define FRONTSWAP_ATTR(_name) \
+ static struct kobj_attribute _name##_attr = \
+ __ATTR(_name, 0644, _name##_show, _name##_store)
+
+static ssize_t curr_pages_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%lu\n", frontswap_curr_pages());
+}
+
+static ssize_t curr_pages_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned long target_pages;
+
+ if (strict_strtoul(buf, 10, &target_pages))
+ return -EINVAL;
+
+ frontswap_shrink(target_pages);
+
+ return count;
+}
+FRONTSWAP_ATTR(curr_pages);
+
+static ssize_t succ_puts_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%lu\n", frontswap_succ_puts);
+}
+FRONTSWAP_ATTR_RO(succ_puts);
+
+static ssize_t failed_puts_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%lu\n", frontswap_failed_puts);
+}
+FRONTSWAP_ATTR_RO(failed_puts);
+
+static ssize_t gets_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%lu\n", frontswap_gets);
+}
+FRONTSWAP_ATTR_RO(gets);
+
+static ssize_t flushes_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%lu\n", frontswap_flushes);
+}
+FRONTSWAP_ATTR_RO(flushes);
+
+static struct attribute *frontswap_attrs[] = {
+ &curr_pages_attr.attr,
+ &succ_puts_attr.attr,
+ &failed_puts_attr.attr,
+ &gets_attr.attr,
+ &flushes_attr.attr,
+ NULL,
+};
+
+static struct attribute_group frontswap_attr_group = {
+ .attrs = frontswap_attrs,
+ .name = "frontswap",
+};
+
+#endif /* CONFIG_SYSFS */
+
+static int __init init_frontswap(void)
+{
+ int err = 0;
+
+#ifdef CONFIG_SYSFS
+ err = sysfs_create_group(mm_kobj, &frontswap_attr_group);
+#endif /* CONFIG_SYSFS */
+ return err;
+}
+
+static void __exit exit_frontswap(void)
+{
+ frontswap_shrink(0UL);
+}
+
+module_init(init_frontswap);
+module_exit(exit_frontswap);
--
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