linux/mm/frontswap.c
<<
>>
Prefs
   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#ifdef CONFIG_DEBUG_FS
  48/*
  49 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
  50 * properly configured).  These are for information only so are not protected
  51 * against increment races.
  52 */
  53static u64 frontswap_loads;
  54static u64 frontswap_succ_stores;
  55static u64 frontswap_failed_stores;
  56static u64 frontswap_invalidates;
  57
  58static inline void inc_frontswap_loads(void) {
  59        frontswap_loads++;
  60}
  61static inline void inc_frontswap_succ_stores(void) {
  62        frontswap_succ_stores++;
  63}
  64static inline void inc_frontswap_failed_stores(void) {
  65        frontswap_failed_stores++;
  66}
  67static inline void inc_frontswap_invalidates(void) {
  68        frontswap_invalidates++;
  69}
  70#else
  71static inline void inc_frontswap_loads(void) { }
  72static inline void inc_frontswap_succ_stores(void) { }
  73static inline void inc_frontswap_failed_stores(void) { }
  74static inline void inc_frontswap_invalidates(void) { }
  75#endif
  76/*
  77 * Register operations for frontswap, returning previous thus allowing
  78 * detection of multiple backends and possible nesting.
  79 */
  80struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
  81{
  82        struct frontswap_ops old = frontswap_ops;
  83
  84        frontswap_ops = *ops;
  85        frontswap_enabled = true;
  86        return old;
  87}
  88EXPORT_SYMBOL(frontswap_register_ops);
  89
  90/*
  91 * Enable/disable frontswap writethrough (see above).
  92 */
  93void frontswap_writethrough(bool enable)
  94{
  95        frontswap_writethrough_enabled = enable;
  96}
  97EXPORT_SYMBOL(frontswap_writethrough);
  98
  99/*
 100 * Called when a swap device is swapon'd.
 101 */
 102void __frontswap_init(unsigned type)
 103{
 104        struct swap_info_struct *sis = swap_info[type];
 105
 106        BUG_ON(sis == NULL);
 107        if (sis->frontswap_map == NULL)
 108                return;
 109        frontswap_ops.init(type);
 110}
 111EXPORT_SYMBOL(__frontswap_init);
 112
 113static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
 114{
 115        frontswap_clear(sis, offset);
 116        atomic_dec(&sis->frontswap_pages);
 117}
 118
 119/*
 120 * "Store" data from a page to frontswap and associate it with the page's
 121 * swaptype and offset.  Page must be locked and in the swap cache.
 122 * If frontswap already contains a page with matching swaptype and
 123 * offset, the frontswap implementation may either overwrite the data and
 124 * return success or invalidate the page from frontswap and return failure.
 125 */
 126int __frontswap_store(struct page *page)
 127{
 128        int ret = -1, dup = 0;
 129        swp_entry_t entry = { .val = page_private(page), };
 130        int type = swp_type(entry);
 131        struct swap_info_struct *sis = swap_info[type];
 132        pgoff_t offset = swp_offset(entry);
 133
 134        BUG_ON(!PageLocked(page));
 135        BUG_ON(sis == NULL);
 136        if (frontswap_test(sis, offset))
 137                dup = 1;
 138        ret = frontswap_ops.store(type, offset, page);
 139        if (ret == 0) {
 140                frontswap_set(sis, offset);
 141                inc_frontswap_succ_stores();
 142                if (!dup)
 143                        atomic_inc(&sis->frontswap_pages);
 144        } else {
 145                /*
 146                  failed dup always results in automatic invalidate of
 147                  the (older) page from frontswap
 148                 */
 149                inc_frontswap_failed_stores();
 150                if (dup)
 151                        __frontswap_clear(sis, offset);
 152        }
 153        if (frontswap_writethrough_enabled)
 154                /* report failure so swap also writes to swap device */
 155                ret = -1;
 156        return ret;
 157}
 158EXPORT_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 */
 165int __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}
 181EXPORT_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 */
 187void __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                __frontswap_clear(sis, offset);
 195                inc_frontswap_invalidates();
 196        }
 197}
 198EXPORT_SYMBOL(__frontswap_invalidate_page);
 199
 200/*
 201 * Invalidate all data from frontswap associated with all offsets for the
 202 * specified swaptype.
 203 */
 204void __frontswap_invalidate_area(unsigned type)
 205{
 206        struct swap_info_struct *sis = swap_info[type];
 207
 208        BUG_ON(sis == NULL);
 209        if (sis->frontswap_map == NULL)
 210                return;
 211        frontswap_ops.invalidate_area(type);
 212        atomic_set(&sis->frontswap_pages, 0);
 213        memset(sis->frontswap_map, 0, sis->max / sizeof(long));
 214}
 215EXPORT_SYMBOL(__frontswap_invalidate_area);
 216
 217static unsigned long __frontswap_curr_pages(void)
 218{
 219        int type;
 220        unsigned long totalpages = 0;
 221        struct swap_info_struct *si = NULL;
 222
 223        assert_spin_locked(&swap_lock);
 224        for (type = swap_list.head; type >= 0; type = si->next) {
 225                si = swap_info[type];
 226                totalpages += atomic_read(&si->frontswap_pages);
 227        }
 228        return totalpages;
 229}
 230
 231static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
 232                                        int *swapid)
 233{
 234        int ret = -EINVAL;
 235        struct swap_info_struct *si = NULL;
 236        int si_frontswap_pages;
 237        unsigned long total_pages_to_unuse = total;
 238        unsigned long pages = 0, pages_to_unuse = 0;
 239        int type;
 240
 241        assert_spin_locked(&swap_lock);
 242        for (type = swap_list.head; type >= 0; type = si->next) {
 243                si = swap_info[type];
 244                si_frontswap_pages = atomic_read(&si->frontswap_pages);
 245                if (total_pages_to_unuse < si_frontswap_pages) {
 246                        pages = pages_to_unuse = total_pages_to_unuse;
 247                } else {
 248                        pages = si_frontswap_pages;
 249                        pages_to_unuse = 0; /* unuse all */
 250                }
 251                /* ensure there is enough RAM to fetch pages from frontswap */
 252                if (security_vm_enough_memory_mm(current->mm, pages)) {
 253                        ret = -ENOMEM;
 254                        continue;
 255                }
 256                vm_unacct_memory(pages);
 257                *unused = pages_to_unuse;
 258                *swapid = type;
 259                ret = 0;
 260                break;
 261        }
 262
 263        return ret;
 264}
 265
 266static int __frontswap_shrink(unsigned long target_pages,
 267                                unsigned long *pages_to_unuse,
 268                                int *type)
 269{
 270        unsigned long total_pages = 0, total_pages_to_unuse;
 271
 272        assert_spin_locked(&swap_lock);
 273
 274        total_pages = __frontswap_curr_pages();
 275        if (total_pages <= target_pages) {
 276                /* Nothing to do */
 277                *pages_to_unuse = 0;
 278                return 0;
 279        }
 280        total_pages_to_unuse = total_pages - target_pages;
 281        return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
 282}
 283
 284/*
 285 * Frontswap, like a true swap device, may unnecessarily retain pages
 286 * under certain circumstances; "shrink" frontswap is essentially a
 287 * "partial swapoff" and works by calling try_to_unuse to attempt to
 288 * unuse enough frontswap pages to attempt to -- subject to memory
 289 * constraints -- reduce the number of pages in frontswap to the
 290 * number given in the parameter target_pages.
 291 */
 292void frontswap_shrink(unsigned long target_pages)
 293{
 294        unsigned long pages_to_unuse = 0;
 295        int type, ret;
 296
 297        /*
 298         * we don't want to hold swap_lock while doing a very
 299         * lengthy try_to_unuse, but swap_list may change
 300         * so restart scan from swap_list.head each time
 301         */
 302        spin_lock(&swap_lock);
 303        ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
 304        spin_unlock(&swap_lock);
 305        if (ret == 0 && pages_to_unuse)
 306                try_to_unuse(type, true, pages_to_unuse);
 307        return;
 308}
 309EXPORT_SYMBOL(frontswap_shrink);
 310
 311/*
 312 * Count and return the number of frontswap pages across all
 313 * swap devices.  This is exported so that backend drivers can
 314 * determine current usage without reading debugfs.
 315 */
 316unsigned long frontswap_curr_pages(void)
 317{
 318        unsigned long totalpages = 0;
 319
 320        spin_lock(&swap_lock);
 321        totalpages = __frontswap_curr_pages();
 322        spin_unlock(&swap_lock);
 323
 324        return totalpages;
 325}
 326EXPORT_SYMBOL(frontswap_curr_pages);
 327
 328static int __init init_frontswap(void)
 329{
 330#ifdef CONFIG_DEBUG_FS
 331        struct dentry *root = debugfs_create_dir("frontswap", NULL);
 332        if (root == NULL)
 333                return -ENXIO;
 334        debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
 335        debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
 336        debugfs_create_u64("failed_stores", S_IRUGO, root,
 337                                &frontswap_failed_stores);
 338        debugfs_create_u64("invalidates", S_IRUGO,
 339                                root, &frontswap_invalidates);
 340#endif
 341        return 0;
 342}
 343
 344module_init(init_frontswap);
 345
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.