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-rw-r--r--mm/frontswap.c283
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diff --git a/mm/frontswap.c b/mm/frontswap.c
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-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Frontswap frontend
- *
- * This code provides the generic "frontend" layer to call a matching
- * "backend" driver implementation of frontswap. See
- * Documentation/mm/frontswap.rst for more information.
- *
- * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
- * Author: Dan Magenheimer
- */
-
-#include <linux/mman.h>
-#include <linux/swap.h>
-#include <linux/swapops.h>
-#include <linux/security.h>
-#include <linux/module.h>
-#include <linux/debugfs.h>
-#include <linux/frontswap.h>
-#include <linux/swapfile.h>
-
-DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
-
-/*
- * frontswap_ops are added by frontswap_register_ops, and provide the
- * frontswap "backend" implementation functions. Multiple implementations
- * may be registered, but implementations can never deregister. This
- * is a simple singly-linked list of all registered implementations.
- */
-static const struct frontswap_ops *frontswap_ops __read_mostly;
-
-#ifdef CONFIG_DEBUG_FS
-/*
- * 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_loads;
-static u64 frontswap_succ_stores;
-static u64 frontswap_failed_stores;
-static u64 frontswap_invalidates;
-
-static inline void inc_frontswap_loads(void)
-{
- data_race(frontswap_loads++);
-}
-static inline void inc_frontswap_succ_stores(void)
-{
- data_race(frontswap_succ_stores++);
-}
-static inline void inc_frontswap_failed_stores(void)
-{
- data_race(frontswap_failed_stores++);
-}
-static inline void inc_frontswap_invalidates(void)
-{
- data_race(frontswap_invalidates++);
-}
-#else
-static inline void inc_frontswap_loads(void) { }
-static inline void inc_frontswap_succ_stores(void) { }
-static inline void inc_frontswap_failed_stores(void) { }
-static inline void inc_frontswap_invalidates(void) { }
-#endif
-
-/*
- * Due to the asynchronous nature of the backends loading potentially
- * _after_ the swap system has been activated, we have chokepoints
- * on all frontswap functions to not call the backend until the backend
- * has registered.
- *
- * This would not guards us against the user deciding to call swapoff right as
- * we are calling the backend to initialize (so swapon is in action).
- * Fortunately for us, the swapon_mutex has been taken by the callee so we are
- * OK. The other scenario where calls to frontswap_store (called via
- * swap_writepage) is racing with frontswap_invalidate_area (called via
- * swapoff) is again guarded by the swap subsystem.
- *
- * While no backend is registered all calls to frontswap_[store|load|
- * invalidate_area|invalidate_page] are ignored or fail.
- *
- * The time between the backend being registered and the swap file system
- * calling the backend (via the frontswap_* functions) is indeterminate as
- * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
- * That is OK as we are comfortable missing some of these calls to the newly
- * registered backend.
- *
- * Obviously the opposite (unloading the backend) must be done after all
- * the frontswap_[store|load|invalidate_area|invalidate_page] start
- * ignoring or failing the requests. However, there is currently no way
- * to unload a backend once it is registered.
- */
-
-/*
- * Register operations for frontswap
- */
-int frontswap_register_ops(const struct frontswap_ops *ops)
-{
- if (frontswap_ops)
- return -EINVAL;
-
- frontswap_ops = ops;
- static_branch_inc(&frontswap_enabled_key);
- return 0;
-}
-
-/*
- * Called when a swap device is swapon'd.
- */
-void frontswap_init(unsigned type, unsigned long *map)
-{
- struct swap_info_struct *sis = swap_info[type];
-
- VM_BUG_ON(sis == NULL);
-
- /*
- * p->frontswap is a bitmap that we MUST have to figure out which page
- * has gone in frontswap. Without it there is no point of continuing.
- */
- if (WARN_ON(!map))
- return;
- /*
- * Irregardless of whether the frontswap backend has been loaded
- * before this function or it will be later, we _MUST_ have the
- * p->frontswap set to something valid to work properly.
- */
- frontswap_map_set(sis, map);
-
- if (!frontswap_enabled())
- return;
- frontswap_ops->init(type);
-}
-
-static bool __frontswap_test(struct swap_info_struct *sis,
- pgoff_t offset)
-{
- if (sis->frontswap_map)
- return test_bit(offset, sis->frontswap_map);
- return false;
-}
-
-static inline void __frontswap_set(struct swap_info_struct *sis,
- pgoff_t offset)
-{
- set_bit(offset, sis->frontswap_map);
- atomic_inc(&sis->frontswap_pages);
-}
-
-static inline void __frontswap_clear(struct swap_info_struct *sis,
- pgoff_t offset)
-{
- clear_bit(offset, sis->frontswap_map);
- atomic_dec(&sis->frontswap_pages);
-}
-
-/*
- * "Store" 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 implementation may either overwrite the data and
- * return success or invalidate the page from frontswap and return failure.
- */
-int __frontswap_store(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);
-
- VM_BUG_ON(!frontswap_ops);
- VM_BUG_ON(!PageLocked(page));
- VM_BUG_ON(sis == NULL);
-
- /*
- * If a dup, we must remove the old page first; we can't leave the
- * old page no matter if the store of the new page succeeds or fails,
- * and we can't rely on the new page replacing the old page as we may
- * not store to the same implementation that contains the old page.
- */
- if (__frontswap_test(sis, offset)) {
- __frontswap_clear(sis, offset);
- frontswap_ops->invalidate_page(type, offset);
- }
-
- ret = frontswap_ops->store(type, offset, page);
- if (ret == 0) {
- __frontswap_set(sis, offset);
- inc_frontswap_succ_stores();
- } else {
- inc_frontswap_failed_stores();
- }
-
- return ret;
-}
-
-/*
- * "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_load(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);
- bool exclusive = false;
-
- VM_BUG_ON(!frontswap_ops);
- VM_BUG_ON(!PageLocked(page));
- VM_BUG_ON(sis == NULL);
-
- if (!__frontswap_test(sis, offset))
- return -1;
-
- /* Try loading from each implementation, until one succeeds. */
- ret = frontswap_ops->load(type, offset, page, &exclusive);
- if (ret == 0) {
- inc_frontswap_loads();
- if (exclusive) {
- SetPageDirty(page);
- __frontswap_clear(sis, offset);
- }
- }
- return ret;
-}
-
-/*
- * 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];
-
- VM_BUG_ON(!frontswap_ops);
- VM_BUG_ON(sis == NULL);
-
- if (!__frontswap_test(sis, offset))
- return;
-
- frontswap_ops->invalidate_page(type, offset);
- __frontswap_clear(sis, offset);
- inc_frontswap_invalidates();
-}
-
-/*
- * 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];
-
- VM_BUG_ON(!frontswap_ops);
- VM_BUG_ON(sis == NULL);
-
- if (sis->frontswap_map == NULL)
- return;
-
- frontswap_ops->invalidate_area(type);
- atomic_set(&sis->frontswap_pages, 0);
- bitmap_zero(sis->frontswap_map, sis->max);
-}
-
-static int __init init_frontswap(void)
-{
-#ifdef CONFIG_DEBUG_FS
- struct dentry *root = debugfs_create_dir("frontswap", NULL);
- if (root == NULL)
- return -ENXIO;
- debugfs_create_u64("loads", 0444, root, &frontswap_loads);
- debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores);
- debugfs_create_u64("failed_stores", 0444, root,
- &frontswap_failed_stores);
- debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates);
-#endif
- return 0;
-}
-
-module_init(init_frontswap);