/* * 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/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> /* * 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. */ bool frontswap_enabled __read_mostly; EXPORT_SYMBOL(frontswap_enabled); /* * If enabled, frontswap_store 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; /* * If enabled, the underlying tmem implementation is capable of doing * exclusive gets, so frontswap_load, on a successful tmem_get must * mark the page as no longer in frontswap AND mark it dirty. */ static bool frontswap_tmem_exclusive_gets_enabled __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) { frontswap_loads++; } static inline void inc_frontswap_succ_stores(void) { frontswap_succ_stores++; } static inline void inc_frontswap_failed_stores(void) { frontswap_failed_stores++; } static inline void inc_frontswap_invalidates(void) { 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 /* * 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 = true; 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); /* * Enable/disable frontswap exclusive gets (see above). */ void frontswap_tmem_exclusive_gets(bool enable) { frontswap_tmem_exclusive_gets_enabled = enable; } EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); /* * 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; frontswap_ops.init(type); } EXPORT_SYMBOL(__frontswap_init); static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset) { frontswap_clear(sis, offset); 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, 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.store(type, offset, page); if (ret == 0) { frontswap_set(sis, offset); inc_frontswap_succ_stores(); if (!dup) atomic_inc(&sis->frontswap_pages); } else { /* failed dup always results in automatic invalidate of the (older) page from frontswap */ inc_frontswap_failed_stores(); if (dup) __frontswap_clear(sis, offset); } if (frontswap_writethrough_enabled) /* report failure so swap also writes to swap device */ ret = -1; return ret; } EXPORT_SYMBOL(__frontswap_store); /* * "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); BUG_ON(!PageLocked(page)); BUG_ON(sis == NULL); if (frontswap_test(sis, offset)) ret = frontswap_ops.load(type, offset, page); if (ret == 0) { inc_frontswap_loads(); if (frontswap_tmem_exclusive_gets_enabled) { SetPageDirty(page); frontswap_clear(sis, offset); } } return ret; } EXPORT_SYMBOL(__frontswap_load); /* * 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); __frontswap_clear(sis, offset); inc_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); static unsigned long __frontswap_curr_pages(void) { int type; unsigned long totalpages = 0; struct swap_info_struct *si = NULL; assert_spin_locked(&swap_lock); for (type = swap_list.head; type >= 0; type = si->next) { si = swap_info[type]; totalpages += atomic_read(&si->frontswap_pages); } return totalpages; } static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, int *swapid) { int ret = -EINVAL; struct swap_info_struct *si = NULL; int si_frontswap_pages; unsigned long total_pages_to_unuse = total; unsigned long pages = 0, pages_to_unuse = 0; int type; assert_spin_locked(&swap_lock); 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)) { ret = -ENOMEM; continue; } vm_unacct_memory(pages); *unused = pages_to_unuse; *swapid = type; ret = 0; break; } return ret; } /* * Used to check if it's necessory and feasible to unuse pages. * Return 1 when nothing to do, 0 when need to shink pages, * error code when there is an error. */ static int __frontswap_shrink(unsigned long target_pages, unsigned long *pages_to_unuse, int *type) { unsigned long total_pages = 0, total_pages_to_unuse; assert_spin_locked(&swap_lock); total_pages = __frontswap_curr_pages(); if (total_pages <= target_pages) { /* Nothing to do */ *pages_to_unuse = 0; return 1; } total_pages_to_unuse = total_pages - target_pages; return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); } /* * 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) { unsigned long pages_to_unuse = 0; int uninitialized_var(type), ret; /* * 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); ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); spin_unlock(&swap_lock); if (ret == 0) try_to_unuse(type, true, pages_to_unuse); 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) { unsigned long totalpages = 0; spin_lock(&swap_lock); totalpages = __frontswap_curr_pages(); spin_unlock(&swap_lock); return totalpages; } EXPORT_SYMBOL(frontswap_curr_pages); 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", S_IRUGO, root, &frontswap_loads); debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); debugfs_create_u64("failed_stores", S_IRUGO, root, &frontswap_failed_stores); debugfs_create_u64("invalidates", S_IRUGO, root, &frontswap_invalidates); #endif return 0; } module_init(init_frontswap);