linux/mm/frontswap.c
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   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/mman.h>
  15#include <linux/swap.h>
  16#include <linux/swapops.h>
  17#include <linux/security.h>
  18#include <linux/module.h>
  19#include <linux/debugfs.h>
  20#include <linux/frontswap.h>
  21#include <linux/swapfile.h>
  22
  23/*
  24 * frontswap_ops is set by frontswap_register_ops to contain the pointers
  25 * to the frontswap "backend" implementation functions.
  26 */
  27static struct frontswap_ops frontswap_ops __read_mostly;
  28
  29/*
  30 * This global enablement flag reduces overhead on systems where frontswap_ops
  31 * has not been registered, so is preferred to the slower alternative: a
  32 * function call that checks a non-global.
  33 */
  34bool frontswap_enabled __read_mostly;
  35EXPORT_SYMBOL(frontswap_enabled);
  36
  37/*
  38 * If enabled, frontswap_store will return failure even on success.  As
  39 * a result, the swap subsystem will always write the page to swap, in
  40 * effect converting frontswap into a writethrough cache.  In this mode,
  41 * there is no direct reduction in swap writes, but a frontswap backend
  42 * can unilaterally "reclaim" any pages in use with no data loss, thus
  43 * providing increases control over maximum memory usage due to frontswap.
  44 */
  45static bool frontswap_writethrough_enabled __read_mostly;
  46
  47/*
  48 * If enabled, the underlying tmem implementation is capable of doing
  49 * exclusive gets, so frontswap_load, on a successful tmem_get must
  50 * mark the page as no longer in frontswap AND mark it dirty.
  51 */
  52static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
  53
  54#ifdef CONFIG_DEBUG_FS
  55/*
  56 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
  57 * properly configured).  These are for information only so are not protected
  58 * against increment races.
  59 */
  60static u64 frontswap_loads;
  61static u64 frontswap_succ_stores;
  62static u64 frontswap_failed_stores;
  63static u64 frontswap_invalidates;
  64
  65static inline void inc_frontswap_loads(void) {
  66        frontswap_loads++;
  67}
  68static inline void inc_frontswap_succ_stores(void) {
  69        frontswap_succ_stores++;
  70}
  71static inline void inc_frontswap_failed_stores(void) {
  72        frontswap_failed_stores++;
  73}
  74static inline void inc_frontswap_invalidates(void) {
  75        frontswap_invalidates++;
  76}
  77#else
  78static inline void inc_frontswap_loads(void) { }
  79static inline void inc_frontswap_succ_stores(void) { }
  80static inline void inc_frontswap_failed_stores(void) { }
  81static inline void inc_frontswap_invalidates(void) { }
  82#endif
  83/*
  84 * Register operations for frontswap, returning previous thus allowing
  85 * detection of multiple backends and possible nesting.
  86 */
  87struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
  88{
  89        struct frontswap_ops old = frontswap_ops;
  90
  91        frontswap_ops = *ops;
  92        frontswap_enabled = true;
  93        return old;
  94}
  95EXPORT_SYMBOL(frontswap_register_ops);
  96
  97/*
  98 * Enable/disable frontswap writethrough (see above).
  99 */
 100void frontswap_writethrough(bool enable)
 101{
 102        frontswap_writethrough_enabled = enable;
 103}
 104EXPORT_SYMBOL(frontswap_writethrough);
 105
 106/*
 107 * Enable/disable frontswap exclusive gets (see above).
 108 */
 109void frontswap_tmem_exclusive_gets(bool enable)
 110{
 111        frontswap_tmem_exclusive_gets_enabled = enable;
 112}
 113EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
 114
 115/*
 116 * Called when a swap device is swapon'd.
 117 */
 118void __frontswap_init(unsigned type)
 119{
 120        struct swap_info_struct *sis = swap_info[type];
 121
 122        BUG_ON(sis == NULL);
 123        if (sis->frontswap_map == NULL)
 124                return;
 125        frontswap_ops.init(type);
 126}
 127EXPORT_SYMBOL(__frontswap_init);
 128
 129static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
 130{
 131        frontswap_clear(sis, offset);
 132        atomic_dec(&sis->frontswap_pages);
 133}
 134
 135/*
 136 * "Store" data from a page to frontswap and associate it with the page's
 137 * swaptype and offset.  Page must be locked and in the swap cache.
 138 * If frontswap already contains a page with matching swaptype and
 139 * offset, the frontswap implementation may either overwrite the data and
 140 * return success or invalidate the page from frontswap and return failure.
 141 */
 142int __frontswap_store(struct page *page)
 143{
 144        int ret = -1, dup = 0;
 145        swp_entry_t entry = { .val = page_private(page), };
 146        int type = swp_type(entry);
 147        struct swap_info_struct *sis = swap_info[type];
 148        pgoff_t offset = swp_offset(entry);
 149
 150        BUG_ON(!PageLocked(page));
 151        BUG_ON(sis == NULL);
 152        if (frontswap_test(sis, offset))
 153                dup = 1;
 154        ret = frontswap_ops.store(type, offset, page);
 155        if (ret == 0) {
 156                frontswap_set(sis, offset);
 157                inc_frontswap_succ_stores();
 158                if (!dup)
 159                        atomic_inc(&sis->frontswap_pages);
 160        } else {
 161                /*
 162                  failed dup always results in automatic invalidate of
 163                  the (older) page from frontswap
 164                 */
 165                inc_frontswap_failed_stores();
 166                if (dup)
 167                        __frontswap_clear(sis, offset);
 168        }
 169        if (frontswap_writethrough_enabled)
 170                /* report failure so swap also writes to swap device */
 171                ret = -1;
 172        return ret;
 173}
 174EXPORT_SYMBOL(__frontswap_store);
 175
 176/*
 177 * "Get" data from frontswap associated with swaptype and offset that were
 178 * specified when the data was put to frontswap and use it to fill the
 179 * specified page with data. Page must be locked and in the swap cache.
 180 */
 181int __frontswap_load(struct page *page)
 182{
 183        int ret = -1;
 184        swp_entry_t entry = { .val = page_private(page), };
 185        int type = swp_type(entry);
 186        struct swap_info_struct *sis = swap_info[type];
 187        pgoff_t offset = swp_offset(entry);
 188
 189        BUG_ON(!PageLocked(page));
 190        BUG_ON(sis == NULL);
 191        if (frontswap_test(sis, offset))
 192                ret = frontswap_ops.load(type, offset, page);
 193        if (ret == 0) {
 194                inc_frontswap_loads();
 195                if (frontswap_tmem_exclusive_gets_enabled) {
 196                        SetPageDirty(page);
 197                        frontswap_clear(sis, offset);
 198                }
 199        }
 200        return ret;
 201}
 202EXPORT_SYMBOL(__frontswap_load);
 203
 204/*
 205 * Invalidate any data from frontswap associated with the specified swaptype
 206 * and offset so that a subsequent "get" will fail.
 207 */
 208void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 209{
 210        struct swap_info_struct *sis = swap_info[type];
 211
 212        BUG_ON(sis == NULL);
 213        if (frontswap_test(sis, offset)) {
 214                frontswap_ops.invalidate_page(type, offset);
 215                __frontswap_clear(sis, offset);
 216                inc_frontswap_invalidates();
 217        }
 218}
 219EXPORT_SYMBOL(__frontswap_invalidate_page);
 220
 221/*
 222 * Invalidate all data from frontswap associated with all offsets for the
 223 * specified swaptype.
 224 */
 225void __frontswap_invalidate_area(unsigned type)
 226{
 227        struct swap_info_struct *sis = swap_info[type];
 228
 229        BUG_ON(sis == NULL);
 230        if (sis->frontswap_map == NULL)
 231                return;
 232        frontswap_ops.invalidate_area(type);
 233        atomic_set(&sis->frontswap_pages, 0);
 234        memset(sis->frontswap_map, 0, sis->max / sizeof(long));
 235}
 236EXPORT_SYMBOL(__frontswap_invalidate_area);
 237
 238static unsigned long __frontswap_curr_pages(void)
 239{
 240        int type;
 241        unsigned long totalpages = 0;
 242        struct swap_info_struct *si = NULL;
 243
 244        assert_spin_locked(&swap_lock);
 245        for (type = swap_list.head; type >= 0; type = si->next) {
 246                si = swap_info[type];
 247                totalpages += atomic_read(&si->frontswap_pages);
 248        }
 249        return totalpages;
 250}
 251
 252static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
 253                                        int *swapid)
 254{
 255        int ret = -EINVAL;
 256        struct swap_info_struct *si = NULL;
 257        int si_frontswap_pages;
 258        unsigned long total_pages_to_unuse = total;
 259        unsigned long pages = 0, pages_to_unuse = 0;
 260        int type;
 261
 262        assert_spin_locked(&swap_lock);
 263        for (type = swap_list.head; type >= 0; type = si->next) {
 264                si = swap_info[type];
 265                si_frontswap_pages = atomic_read(&si->frontswap_pages);
 266                if (total_pages_to_unuse < si_frontswap_pages) {
 267                        pages = pages_to_unuse = total_pages_to_unuse;
 268                } else {
 269                        pages = si_frontswap_pages;
 270                        pages_to_unuse = 0; /* unuse all */
 271                }
 272                /* ensure there is enough RAM to fetch pages from frontswap */
 273                if (security_vm_enough_memory_mm(current->mm, pages)) {
 274                        ret = -ENOMEM;
 275                        continue;
 276                }
 277                vm_unacct_memory(pages);
 278                *unused = pages_to_unuse;
 279                *swapid = type;
 280                ret = 0;
 281                break;
 282        }
 283
 284        return ret;
 285}
 286
 287/*
 288 * Used to check if it's necessory and feasible to unuse pages.
 289 * Return 1 when nothing to do, 0 when need to shink pages,
 290 * error code when there is an error.
 291 */
 292static int __frontswap_shrink(unsigned long target_pages,
 293                                unsigned long *pages_to_unuse,
 294                                int *type)
 295{
 296        unsigned long total_pages = 0, total_pages_to_unuse;
 297
 298        assert_spin_locked(&swap_lock);
 299
 300        total_pages = __frontswap_curr_pages();
 301        if (total_pages <= target_pages) {
 302                /* Nothing to do */
 303                *pages_to_unuse = 0;
 304                return 1;
 305        }
 306        total_pages_to_unuse = total_pages - target_pages;
 307        return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
 308}
 309
 310/*
 311 * Frontswap, like a true swap device, may unnecessarily retain pages
 312 * under certain circumstances; "shrink" frontswap is essentially a
 313 * "partial swapoff" and works by calling try_to_unuse to attempt to
 314 * unuse enough frontswap pages to attempt to -- subject to memory
 315 * constraints -- reduce the number of pages in frontswap to the
 316 * number given in the parameter target_pages.
 317 */
 318void frontswap_shrink(unsigned long target_pages)
 319{
 320        unsigned long pages_to_unuse = 0;
 321        int uninitialized_var(type), ret;
 322
 323        /*
 324         * we don't want to hold swap_lock while doing a very
 325         * lengthy try_to_unuse, but swap_list may change
 326         * so restart scan from swap_list.head each time
 327         */
 328        spin_lock(&swap_lock);
 329        ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
 330        spin_unlock(&swap_lock);
 331        if (ret == 0)
 332                try_to_unuse(type, true, pages_to_unuse);
 333        return;
 334}
 335EXPORT_SYMBOL(frontswap_shrink);
 336
 337/*
 338 * Count and return the number of frontswap pages across all
 339 * swap devices.  This is exported so that backend drivers can
 340 * determine current usage without reading debugfs.
 341 */
 342unsigned long frontswap_curr_pages(void)
 343{
 344        unsigned long totalpages = 0;
 345
 346        spin_lock(&swap_lock);
 347        totalpages = __frontswap_curr_pages();
 348        spin_unlock(&swap_lock);
 349
 350        return totalpages;
 351}
 352EXPORT_SYMBOL(frontswap_curr_pages);
 353
 354static int __init init_frontswap(void)
 355{
 356#ifdef CONFIG_DEBUG_FS
 357        struct dentry *root = debugfs_create_dir("frontswap", NULL);
 358        if (root == NULL)
 359                return -ENXIO;
 360        debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
 361        debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
 362        debugfs_create_u64("failed_stores", S_IRUGO, root,
 363                                &frontswap_failed_stores);
 364        debugfs_create_u64("invalidates", S_IRUGO,
 365                                root, &frontswap_invalidates);
 366#endif
 367        return 0;
 368}
 369
 370module_init(init_frontswap);
 371
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