--- /dev/null
+/*
+ * 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) 2009-2012 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/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/debugfs.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 __read_mostly;
+
+/*
+ * 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 __read_mostly;
+EXPORT_SYMBOL(frontswap_enabled);
+
+/*
+ * If enabled, frontswap_put will return failure even on success. As
+ * a result, the swap subsystem will always write the page to swap, in
+ * effect converting frontswap into a writethrough cache. In this mode,
+ * there is no direct reduction in swap writes, but a frontswap backend
+ * can unilaterally "reclaim" any pages in use with no data loss, thus
+ * providing increases control over maximum memory usage due to frontswap.
+ */
+static bool frontswap_writethrough_enabled __read_mostly;
+
+/*
+ * Counters available via /sys/kernel/debug/frontswap (if debugfs is
+ * properly configured. These are for information only so are not protected
+ * against increment races.
+ */
+static u64 frontswap_gets;
+static u64 frontswap_succ_puts;
+static u64 frontswap_failed_puts;
+static u64 frontswap_invalidates;
+
+/*
+ * 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);
+
+/*
+ * Enable/disable frontswap writethrough (see above)
+ */
+void frontswap_writethrough(bool enable)
+{
+ frontswap_writethrough_enabled = enable;
+}
+EXPORT_SYMBOL(frontswap_writethrough);
+
+/* 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 invalidate 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)
+ atomic_inc(&sis->frontswap_pages);
+ } else if (dup) {
+ /*
+ failed dup always results in automatic invalidate of
+ the (older) page from frontswap
+ */
+ frontswap_clear(sis, offset);
+ atomic_dec(&sis->frontswap_pages);
+ frontswap_failed_puts++;
+ } else
+ frontswap_failed_puts++;
+ if (frontswap_writethrough_enabled)
+ /* report failure so swap also writes to swap device */
+ ret = -1;
+ 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);
+
+/*
+ * Invalidate any data from frontswap associated with the specified swaptype
+ * and offset so that a subsequent "get" will fail.
+ */
+void __frontswap_invalidate_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.invalidate_page)(type, offset);
+ atomic_dec(&sis->frontswap_pages);
+ frontswap_clear(sis, offset);
+ frontswap_invalidates++;
+ }
+}
+EXPORT_SYMBOL(__frontswap_invalidate_page);
+
+/*
+ * Invalidate all data from frontswap associated with all offsets for the
+ * specified swaptype.
+ */
+void __frontswap_invalidate_area(unsigned type)
+{
+ struct swap_info_struct *sis = swap_info[type];
+
+ BUG_ON(sis == NULL);
+ if (sis->frontswap_map == NULL)
+ return;
+ (*frontswap_ops.invalidate_area)(type);
+ atomic_set(&sis->frontswap_pages, 0);
+ memset(sis->frontswap_map, 0, sis->max / sizeof(long));
+}
+EXPORT_SYMBOL(__frontswap_invalidate_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 to the
+ * number given in the parameter target_pages.
+ */
+void frontswap_shrink(unsigned long target_pages)
+{
+ struct swap_info_struct *si = NULL;
+ int si_frontswap_pages;
+ unsigned long total_pages = 0, total_pages_to_unuse;
+ unsigned long pages = 0, pages_to_unuse = 0;
+ int type;
+ bool locked = false;
+
+ /*
+ * 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 += atomic_read(&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];
+ si_frontswap_pages = atomic_read(&si->frontswap_pages);
+ 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 */
+ }
+ /* ensure there is enough RAM to fetch pages from frontswap */
+ if (security_vm_enough_memory_mm(current->mm, 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 frontswap pages across all
+ * swap devices. This is exported so that backend drivers can
+ * determine current usage without reading debugfs.
+ */
+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];
+ totalpages += atomic_read(&si->frontswap_pages);
+ }
+ spin_unlock(&swap_lock);
+ return totalpages;
+}
+EXPORT_SYMBOL(frontswap_curr_pages);
+
+static int __init init_frontswap(void)
+{
+ int err = 0;
+
+#ifdef CONFIG_DEBUG_FS
+ struct dentry *root = debugfs_create_dir("frontswap", NULL);
+ if (root == NULL)
+ return -ENXIO;
+ debugfs_create_u64("gets", S_IRUGO, root, &frontswap_gets);
+ debugfs_create_u64("succ_puts", S_IRUGO, root, &frontswap_succ_puts);
+ debugfs_create_u64("failed_puts", S_IRUGO, root,
+ &frontswap_failed_puts);
+ debugfs_create_u64("invalidates", S_IRUGO,
+ root, &frontswap_invalidates);
+#endif
+ return err;
+}
+
+module_init(init_frontswap);
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