mm/frontswap.c

   1 /*
   2  * Frontswap frontend
   3  *
   4  * This code provides the generic "frontend" layer to call a matching
   5  * "backend" driver implementation of frontswap.  See
   6  * Documentation/vm/frontswap.txt for more information.
   7  *
   8  * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
   9  * Author: Dan Magenheimer
  10  *
  11  * This work is licensed under the terms of the GNU GPL, version 2.
  12  */
  13
  14 #include <linux/mm.h>
  15 #include <linux/mman.h>
  16 #include <linux/swap.h>
  17 #include <linux/swapops.h>
  18 #include <linux/proc_fs.h>
  19 #include <linux/security.h>
  20 #include <linux/capability.h>
  21 #include <linux/module.h>
  22 #include <linux/uaccess.h>
  23 #include <linux/debugfs.h>
  24 #include <linux/frontswap.h>
  25 #include <linux/swapfile.h>
  26
  27 /*
  28  * frontswap_ops is set by frontswap_register_ops to contain the pointers
  29  * to the frontswap "backend" implementation functions.
  30  */
  31 static struct frontswap_ops frontswap_ops __read_mostly;
  32
  33 /*
  34  * This global enablement flag reduces overhead on systems where frontswap_ops
  35  * has not been registered, so is preferred to the slower alternative: a
  36  * function call that checks a non-global.
  37  */
  38 bool frontswap_enabled __read_mostly;
  39 EXPORT_SYMBOL(frontswap_enabled);
  40
  41 /*
  42  * If enabled, frontswap_store will return failure even on success.  As
  43  * a result, the swap subsystem will always write the page to swap, in
  44  * effect converting frontswap into a writethrough cache.  In this mode,
  45  * there is no direct reduction in swap writes, but a frontswap backend
  46  * can unilaterally "reclaim" any pages in use with no data loss, thus
  47  * providing increases control over maximum memory usage due to frontswap.
  48  */
  49 static bool frontswap_writethrough_enabled __read_mostly;
  50
  51 #ifdef CONFIG_DEBUG_FS
  52 /*
  53  * Counters available via /sys/kernel/debug/frontswap (if debugfs is
  54  * properly configured).  These are for information only so are not protected
  55  * against increment races.
  56  */
  57 static u64 frontswap_loads;
  58 static u64 frontswap_succ_stores;
  59 static u64 frontswap_failed_stores;
  60 static u64 frontswap_invalidates;
  61
  62 static inline void inc_frontswap_loads(void) {
  63         frontswap_loads++;
  64 }
  65 static inline void inc_frontswap_succ_stores(void) {
  66         frontswap_succ_stores++;
  67 }
  68 static inline void inc_frontswap_failed_stores(void) {
  69         frontswap_failed_stores++;
  70 }
  71 static inline void inc_frontswap_invalidates(void) {
  72         frontswap_invalidates++;
  73 }
  74 #else
  75 static inline void inc_frontswap_loads(void) { }
  76 static inline void inc_frontswap_succ_stores(void) { }
  77 static inline void inc_frontswap_failed_stores(void) { }
  78 static inline void inc_frontswap_invalidates(void) { }
  79 #endif
  80 /*
  81  * Register operations for frontswap, returning previous thus allowing
  82  * detection of multiple backends and possible nesting.
  83  */
  84 struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
  85 {
  86         struct frontswap_ops old = frontswap_ops;
  87
  88         frontswap_ops = *ops;
  89         frontswap_enabled = true;
  90         return old;
  91 }
  92 EXPORT_SYMBOL(frontswap_register_ops);
  93
  94 /*
  95  * Enable/disable frontswap writethrough (see above).
  96  */
  97 void frontswap_writethrough(bool enable)
  98 {
  99         frontswap_writethrough_enabled = enable;
 100 }
 101 EXPORT_SYMBOL(frontswap_writethrough);
 102
 103 /*
 104  * Called when a swap device is swapon'd.
 105  */
 106 void __frontswap_init(unsigned type)
 107 {
 108         struct swap_info_struct *sis = swap_info[type];
 109
 110         BUG_ON(sis == NULL);
 111         if (sis->frontswap_map == NULL)
 112                 return;
 113         if (frontswap_enabled)
 114                 (*frontswap_ops.init)(type);
 115 }
 116 EXPORT_SYMBOL(__frontswap_init);
 117
 118 /*
 119  * "Store" data from a page to frontswap and associate it with the page's
 120  * swaptype and offset.  Page must be locked and in the swap cache.
 121  * If frontswap already contains a page with matching swaptype and
 122  * offset, the frontswap implmentation may either overwrite the data and
 123  * return success or invalidate the page from frontswap and return failure.
 124  */
 125 int __frontswap_store(struct page *page)
 126 {
 127         int ret = -1, dup = 0;
 128         swp_entry_t entry = { .val = page_private(page), };
 129         int type = swp_type(entry);
 130         struct swap_info_struct *sis = swap_info[type];
 131         pgoff_t offset = swp_offset(entry);
 132
 133         BUG_ON(!PageLocked(page));
 134         BUG_ON(sis == NULL);
 135         if (frontswap_test(sis, offset))
 136                 dup = 1;
 137         ret = (*frontswap_ops.store)(type, offset, page);
 138         if (ret == 0) {
 139                 frontswap_set(sis, offset);
 140                 inc_frontswap_succ_stores();
 141                 if (!dup)
 142                         atomic_inc(&sis->frontswap_pages);
 143         } else if (dup) {
 144                 /*
 145                   failed dup always results in automatic invalidate of
 146                   the (older) page from frontswap
 147                  */
 148                 frontswap_clear(sis, offset);
 149                 atomic_dec(&sis->frontswap_pages);
 150                 inc_frontswap_failed_stores();
 151         } else
 152                 inc_frontswap_failed_stores();
 153         if (frontswap_writethrough_enabled)
 154                 /* report failure so swap also writes to swap device */
 155                 ret = -1;
 156         return ret;
 157 }
 158 EXPORT_SYMBOL(__frontswap_store);
 159
 160 /*
 161  * "Get" data from frontswap associated with swaptype and offset that were
 162  * specified when the data was put to frontswap and use it to fill the
 163  * specified page with data. Page must be locked and in the swap cache.
 164  */
 165 int __frontswap_load(struct page *page)
 166 {
 167         int ret = -1;
 168         swp_entry_t entry = { .val = page_private(page), };
 169         int type = swp_type(entry);
 170         struct swap_info_struct *sis = swap_info[type];
 171         pgoff_t offset = swp_offset(entry);
 172
 173         BUG_ON(!PageLocked(page));
 174         BUG_ON(sis == NULL);
 175         if (frontswap_test(sis, offset))
 176                 ret = (*frontswap_ops.load)(type, offset, page);
 177         if (ret == 0)
 178                 inc_frontswap_loads();
 179         return ret;
 180 }
 181 EXPORT_SYMBOL(__frontswap_load);
 182
 183 /*
 184  * Invalidate any data from frontswap associated with the specified swaptype
 185  * and offset so that a subsequent "get" will fail.
 186  */
 187 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 188 {
 189         struct swap_info_struct *sis = swap_info[type];
 190
 191         BUG_ON(sis == NULL);
 192         if (frontswap_test(sis, offset)) {
 193                 (*frontswap_ops.invalidate_page)(type, offset);
 194                 atomic_dec(&sis->frontswap_pages);
 195                 frontswap_clear(sis, offset);
 196                 inc_frontswap_invalidates();
 197         }
 198 }
 199 EXPORT_SYMBOL(__frontswap_invalidate_page);
 200
 201 /*
 202  * Invalidate all data from frontswap associated with all offsets for the
 203  * specified swaptype.
 204  */
 205 void __frontswap_invalidate_area(unsigned type)
 206 {
 207         struct swap_info_struct *sis = swap_info[type];
 208
 209         BUG_ON(sis == NULL);
 210         if (sis->frontswap_map == NULL)
 211                 return;
 212         (*frontswap_ops.invalidate_area)(type);
 213         atomic_set(&sis->frontswap_pages, 0);
 214         memset(sis->frontswap_map, 0, sis->max / sizeof(long));
 215 }
 216 EXPORT_SYMBOL(__frontswap_invalidate_area);
 217
 218 /*
 219  * Frontswap, like a true swap device, may unnecessarily retain pages
 220  * under certain circumstances; "shrink" frontswap is essentially a
 221  * "partial swapoff" and works by calling try_to_unuse to attempt to
 222  * unuse enough frontswap pages to attempt to -- subject to memory
 223  * constraints -- reduce the number of pages in frontswap to the
 224  * number given in the parameter target_pages.
 225  */
 226 void frontswap_shrink(unsigned long target_pages)
 227 {
 228         struct swap_info_struct *si = NULL;
 229         int si_frontswap_pages;
 230         unsigned long total_pages = 0, total_pages_to_unuse;
 231         unsigned long pages = 0, pages_to_unuse = 0;
 232         int type;
 233         bool locked = false;
 234
 235         /*
 236          * we don't want to hold swap_lock while doing a very
 237          * lengthy try_to_unuse, but swap_list may change
 238          * so restart scan from swap_list.head each time
 239          */
 240         spin_lock(&swap_lock);
 241         locked = true;
 242         total_pages = 0;
 243         for (type = swap_list.head; type >= 0; type = si->next) {
 244                 si = swap_info[type];
 245                 total_pages += atomic_read(&si->frontswap_pages);
 246         }
 247         if (total_pages <= target_pages)
 248                 goto out;
 249         total_pages_to_unuse = total_pages - target_pages;
 250         for (type = swap_list.head; type >= 0; type = si->next) {
 251                 si = swap_info[type];
 252                 si_frontswap_pages = atomic_read(&si->frontswap_pages);
 253                 if (total_pages_to_unuse < si_frontswap_pages)
 254                         pages = pages_to_unuse = total_pages_to_unuse;
 255                 else {
 256                         pages = si_frontswap_pages;
 257                         pages_to_unuse = 0; /* unuse all */
 258                 }
 259                 /* ensure there is enough RAM to fetch pages from frontswap */
 260                 if (security_vm_enough_memory_mm(current->mm, pages))
 261                         continue;
 262                 vm_unacct_memory(pages);
 263                 break;
 264         }
 265         if (type < 0)
 266                 goto out;
 267         locked = false;
 268         spin_unlock(&swap_lock);
 269         try_to_unuse(type, true, pages_to_unuse);
 270 out:
 271         if (locked)
 272                 spin_unlock(&swap_lock);
 273         return;
 274 }
 275 EXPORT_SYMBOL(frontswap_shrink);
 276
 277 /*
 278  * Count and return the number of frontswap pages across all
 279  * swap devices.  This is exported so that backend drivers can
 280  * determine current usage without reading debugfs.
 281  */
 282 unsigned long frontswap_curr_pages(void)
 283 {
 284         int type;
 285         unsigned long totalpages = 0;
 286         struct swap_info_struct *si = NULL;
 287
 288         spin_lock(&swap_lock);
 289         for (type = swap_list.head; type >= 0; type = si->next) {
 290                 si = swap_info[type];
 291                 totalpages += atomic_read(&si->frontswap_pages);
 292         }
 293         spin_unlock(&swap_lock);
 294         return totalpages;
 295 }
 296 EXPORT_SYMBOL(frontswap_curr_pages);
 297
 298 static int __init init_frontswap(void)
 299 {
 300 #ifdef CONFIG_DEBUG_FS
 301         struct dentry *root = debugfs_create_dir("frontswap", NULL);
 302         if (root == NULL)
 303                 return -ENXIO;
 304         debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
 305         debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
 306         debugfs_create_u64("failed_stores", S_IRUGO, root,
 307                                 &frontswap_failed_stores);
 308         debugfs_create_u64("invalidates", S_IRUGO,
 309                                 root, &frontswap_invalidates);
 310 #endif
 311         return 0;
 312 }
 313
 314 module_init(init_frontswap);