arch/powerpc/platforms/pseries/cmm.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Collaborative memory management interface.
   4  *
   5  * Copyright (C) 2008 IBM Corporation
   6  * Author(s): Brian King (brking@linux.vnet.ibm.com),
   7  */
   8
   9 #include <linux/ctype.h>
  10 #include <linux/delay.h>
  11 #include <linux/errno.h>
  12 #include <linux/fs.h>
  13 #include <linux/gfp.h>
  14 #include <linux/kthread.h>
  15 #include <linux/module.h>
  16 #include <linux/oom.h>
  17 #include <linux/reboot.h>
  18 #include <linux/sched.h>
  19 #include <linux/stringify.h>
  20 #include <linux/swap.h>
  21 #include <linux/device.h>
  22 #include <linux/mount.h>
  23 #include <linux/pseudo_fs.h>
  24 #include <linux/magic.h>
  25 #include <linux/balloon_compaction.h>
  26 #include <asm/firmware.h>
  27 #include <asm/hvcall.h>
  28 #include <asm/mmu.h>
  29 #include <asm/pgalloc.h>
  30 #include <linux/uaccess.h>
  31 #include <linux/memory.h>
  32 #include <asm/plpar_wrappers.h>
  33
  34 #include "pseries.h"
  35
  36 #define CMM_DRIVER_VERSION      "1.0.0"
  37 #define CMM_DEFAULT_DELAY       1
  38 #define CMM_HOTPLUG_DELAY       5
  39 #define CMM_DEBUG                       0
  40 #define CMM_DISABLE             0
  41 #define CMM_OOM_KB              1024
  42 #define CMM_MIN_MEM_MB          256
  43 #define KB2PAGES(_p)            ((_p)>>(PAGE_SHIFT-10))
  44 #define PAGES2KB(_p)            ((_p)<<(PAGE_SHIFT-10))
  45
  46 #define CMM_MEM_HOTPLUG_PRI     1
  47
  48 static unsigned int delay = CMM_DEFAULT_DELAY;
  49 static unsigned int hotplug_delay = CMM_HOTPLUG_DELAY;
  50 static unsigned int oom_kb = CMM_OOM_KB;
  51 static unsigned int cmm_debug = CMM_DEBUG;
  52 static unsigned int cmm_disabled = CMM_DISABLE;
  53 static unsigned long min_mem_mb = CMM_MIN_MEM_MB;
  54 static struct device cmm_dev;
  55
  56 MODULE_AUTHOR("Brian King <brking@linux.vnet.ibm.com>");
  57 MODULE_DESCRIPTION("IBM System p Collaborative Memory Manager");
  58 MODULE_LICENSE("GPL");
  59 MODULE_VERSION(CMM_DRIVER_VERSION);
  60
  61 module_param_named(delay, delay, uint, 0644);
  62 MODULE_PARM_DESC(delay, "Delay (in seconds) between polls to query hypervisor paging requests. "
  63                  "[Default=" __stringify(CMM_DEFAULT_DELAY) "]");
  64 module_param_named(hotplug_delay, hotplug_delay, uint, 0644);
  65 MODULE_PARM_DESC(hotplug_delay, "Delay (in seconds) after memory hotplug remove "
  66                  "before loaning resumes. "
  67                  "[Default=" __stringify(CMM_HOTPLUG_DELAY) "]");
  68 module_param_named(oom_kb, oom_kb, uint, 0644);
  69 MODULE_PARM_DESC(oom_kb, "Amount of memory in kb to free on OOM. "
  70                  "[Default=" __stringify(CMM_OOM_KB) "]");
  71 module_param_named(min_mem_mb, min_mem_mb, ulong, 0644);
  72 MODULE_PARM_DESC(min_mem_mb, "Minimum amount of memory (in MB) to not balloon. "
  73                  "[Default=" __stringify(CMM_MIN_MEM_MB) "]");
  74 module_param_named(debug, cmm_debug, uint, 0644);
  75 MODULE_PARM_DESC(debug, "Enable module debugging logging. Set to 1 to enable. "
  76                  "[Default=" __stringify(CMM_DEBUG) "]");
  77
  78 #define cmm_dbg(...) if (cmm_debug) { printk(KERN_INFO "cmm: "__VA_ARGS__); }
  79
  80 static atomic_long_t loaned_pages;
  81 static unsigned long loaned_pages_target;
  82 static unsigned long oom_freed_pages;
  83
  84 static DEFINE_MUTEX(hotplug_mutex);
  85 static int hotplug_occurred; /* protected by the hotplug mutex */
  86
  87 static struct task_struct *cmm_thread_ptr;
  88 static struct balloon_dev_info b_dev_info;
  89
  90 static long plpar_page_set_loaned(struct page *page)
  91 {
  92         const unsigned long vpa = page_to_phys(page);
  93         unsigned long cmo_page_sz = cmo_get_page_size();
  94         long rc = 0;
  95         int i;
  96
  97         for (i = 0; !rc && i < PAGE_SIZE; i += cmo_page_sz)
  98                 rc = plpar_hcall_norets(H_PAGE_INIT, H_PAGE_SET_LOANED, vpa + i, 0);
  99
 100         for (i -= cmo_page_sz; rc && i != 0; i -= cmo_page_sz)
 101                 plpar_hcall_norets(H_PAGE_INIT, H_PAGE_SET_ACTIVE,
 102                                    vpa + i - cmo_page_sz, 0);
 103
 104         return rc;
 105 }
 106
 107 static long plpar_page_set_active(struct page *page)
 108 {
 109         const unsigned long vpa = page_to_phys(page);
 110         unsigned long cmo_page_sz = cmo_get_page_size();
 111         long rc = 0;
 112         int i;
 113
 114         for (i = 0; !rc && i < PAGE_SIZE; i += cmo_page_sz)
 115                 rc = plpar_hcall_norets(H_PAGE_INIT, H_PAGE_SET_ACTIVE, vpa + i, 0);
 116
 117         for (i -= cmo_page_sz; rc && i != 0; i -= cmo_page_sz)
 118                 plpar_hcall_norets(H_PAGE_INIT, H_PAGE_SET_LOANED,
 119                                    vpa + i - cmo_page_sz, 0);
 120
 121         return rc;
 122 }
 123
 124 /**
 125  * cmm_alloc_pages - Allocate pages and mark them as loaned
 126  * @nr: number of pages to allocate
 127  *
 128  * Return value:
 129  *      number of pages requested to be allocated which were not
 130  **/
 131 static long cmm_alloc_pages(long nr)
 132 {
 133         struct page *page;
 134         long rc;
 135
 136         cmm_dbg("Begin request for %ld pages\n", nr);
 137
 138         while (nr) {
 139                 /* Exit if a hotplug operation is in progress or occurred */
 140                 if (mutex_trylock(&hotplug_mutex)) {
 141                         if (hotplug_occurred) {
 142                                 mutex_unlock(&hotplug_mutex);
 143                                 break;
 144                         }
 145                         mutex_unlock(&hotplug_mutex);
 146                 } else {
 147                         break;
 148                 }
 149
 150                 page = balloon_page_alloc();
 151                 if (!page)
 152                         break;
 153                 rc = plpar_page_set_loaned(page);
 154                 if (rc) {
 155                         pr_err("%s: Can not set page to loaned. rc=%ld\n", __func__, rc);
 156                         __free_page(page);
 157                         break;
 158                 }
 159
 160                 balloon_page_enqueue(&b_dev_info, page);
 161                 atomic_long_inc(&loaned_pages);
 162                 adjust_managed_page_count(page, -1);
 163                 nr--;
 164         }
 165
 166         cmm_dbg("End request with %ld pages unfulfilled\n", nr);
 167         return nr;
 168 }
 169
 170 /**
 171  * cmm_free_pages - Free pages and mark them as active
 172  * @nr: number of pages to free
 173  *
 174  * Return value:
 175  *      number of pages requested to be freed which were not
 176  **/
 177 static long cmm_free_pages(long nr)
 178 {
 179         struct page *page;
 180
 181         cmm_dbg("Begin free of %ld pages.\n", nr);
 182         while (nr) {
 183                 page = balloon_page_dequeue(&b_dev_info);
 184                 if (!page)
 185                         break;
 186                 plpar_page_set_active(page);
 187                 adjust_managed_page_count(page, 1);
 188                 __free_page(page);
 189                 atomic_long_dec(&loaned_pages);
 190                 nr--;
 191         }
 192         cmm_dbg("End request with %ld pages unfulfilled\n", nr);
 193         return nr;
 194 }
 195
 196 /**
 197  * cmm_oom_notify - OOM notifier
 198  * @self:       notifier block struct
 199  * @dummy:      not used
 200  * @parm:       returned - number of pages freed
 201  *
 202  * Return value:
 203  *      NOTIFY_OK
 204  **/
 205 static int cmm_oom_notify(struct notifier_block *self,
 206                           unsigned long dummy, void *parm)
 207 {
 208         unsigned long *freed = parm;
 209         long nr = KB2PAGES(oom_kb);
 210
 211         cmm_dbg("OOM processing started\n");
 212         nr = cmm_free_pages(nr);
 213         loaned_pages_target = atomic_long_read(&loaned_pages);
 214         *freed += KB2PAGES(oom_kb) - nr;
 215         oom_freed_pages += KB2PAGES(oom_kb) - nr;
 216         cmm_dbg("OOM processing complete\n");
 217         return NOTIFY_OK;
 218 }
 219
 220 /**
 221  * cmm_get_mpp - Read memory performance parameters
 222  *
 223  * Makes hcall to query the current page loan request from the hypervisor.
 224  *
 225  * Return value:
 226  *      nothing
 227  **/
 228 static void cmm_get_mpp(void)
 229 {
 230         const long __loaned_pages = atomic_long_read(&loaned_pages);
 231         const long total_pages = totalram_pages() + __loaned_pages;
 232         int rc;
 233         struct hvcall_mpp_data mpp_data;
 234         signed long active_pages_target, page_loan_request, target;
 235         signed long min_mem_pages = (min_mem_mb * 1024 * 1024) / PAGE_SIZE;
 236
 237         rc = h_get_mpp(&mpp_data);
 238
 239         if (rc != H_SUCCESS)
 240                 return;
 241
 242         page_loan_request = div_s64((s64)mpp_data.loan_request, PAGE_SIZE);
 243         target = page_loan_request + __loaned_pages;
 244
 245         if (target < 0 || total_pages < min_mem_pages)
 246                 target = 0;
 247
 248         if (target > oom_freed_pages)
 249                 target -= oom_freed_pages;
 250         else
 251                 target = 0;
 252
 253         active_pages_target = total_pages - target;
 254
 255         if (min_mem_pages > active_pages_target)
 256                 target = total_pages - min_mem_pages;
 257
 258         if (target < 0)
 259                 target = 0;
 260
 261         loaned_pages_target = target;
 262
 263         cmm_dbg("delta = %ld, loaned = %lu, target = %lu, oom = %lu, totalram = %lu\n",
 264                 page_loan_request, __loaned_pages, loaned_pages_target,
 265                 oom_freed_pages, totalram_pages());
 266 }
 267
 268 static struct notifier_block cmm_oom_nb = {
 269         .notifier_call = cmm_oom_notify
 270 };
 271
 272 /**
 273  * cmm_thread - CMM task thread
 274  * @dummy:      not used
 275  *
 276  * Return value:
 277  *      0
 278  **/
 279 static int cmm_thread(void *dummy)
 280 {
 281         unsigned long timeleft;
 282         long __loaned_pages;
 283
 284         while (1) {
 285                 timeleft = msleep_interruptible(delay * 1000);
 286
 287                 if (kthread_should_stop() || timeleft)
 288                         break;
 289
 290                 if (mutex_trylock(&hotplug_mutex)) {
 291                         if (hotplug_occurred) {
 292                                 hotplug_occurred = 0;
 293                                 mutex_unlock(&hotplug_mutex);
 294                                 cmm_dbg("Hotplug operation has occurred, "
 295                                                 "loaning activity suspended "
 296                                                 "for %d seconds.\n",
 297                                                 hotplug_delay);
 298                                 timeleft = msleep_interruptible(hotplug_delay *
 299                                                 1000);
 300                                 if (kthread_should_stop() || timeleft)
 301                                         break;
 302                                 continue;
 303                         }
 304                         mutex_unlock(&hotplug_mutex);
 305                 } else {
 306                         cmm_dbg("Hotplug operation in progress, activity "
 307                                         "suspended\n");
 308                         continue;
 309                 }
 310
 311                 cmm_get_mpp();
 312
 313                 __loaned_pages = atomic_long_read(&loaned_pages);
 314                 if (loaned_pages_target > __loaned_pages) {
 315                         if (cmm_alloc_pages(loaned_pages_target - __loaned_pages))
 316                                 loaned_pages_target = __loaned_pages;
 317                 } else if (loaned_pages_target < __loaned_pages)
 318                         cmm_free_pages(__loaned_pages - loaned_pages_target);
 319         }
 320         return 0;
 321 }
 322
 323 #define CMM_SHOW(name, format, args...)                 \
 324         static ssize_t show_##name(struct device *dev,  \
 325                                    struct device_attribute *attr,       \
 326                                    char *buf)                   \
 327         {                                                       \
 328                 return sprintf(buf, format, ##args);            \
 329         }                                                       \
 330         static DEVICE_ATTR(name, 0444, show_##name, NULL)
 331
 332 CMM_SHOW(loaned_kb, "%lu\n", PAGES2KB(atomic_long_read(&loaned_pages)));
 333 CMM_SHOW(loaned_target_kb, "%lu\n", PAGES2KB(loaned_pages_target));
 334
 335 static ssize_t show_oom_pages(struct device *dev,
 336                               struct device_attribute *attr, char *buf)
 337 {
 338         return sprintf(buf, "%lu\n", PAGES2KB(oom_freed_pages));
 339 }
 340
 341 static ssize_t store_oom_pages(struct device *dev,
 342                                struct device_attribute *attr,
 343                                const char *buf, size_t count)
 344 {
 345         unsigned long val = simple_strtoul (buf, NULL, 10);
 346
 347         if (!capable(CAP_SYS_ADMIN))
 348                 return -EPERM;
 349         if (val != 0)
 350                 return -EBADMSG;
 351
 352         oom_freed_pages = 0;
 353         return count;
 354 }
 355
 356 static DEVICE_ATTR(oom_freed_kb, 0644,
 357                    show_oom_pages, store_oom_pages);
 358
 359 static struct device_attribute *cmm_attrs[] = {
 360         &dev_attr_loaned_kb,
 361         &dev_attr_loaned_target_kb,
 362         &dev_attr_oom_freed_kb,
 363 };
 364
 365 static struct bus_type cmm_subsys = {
 366         .name = "cmm",
 367         .dev_name = "cmm",
 368 };
 369
 370 static void cmm_release_device(struct device *dev)
 371 {
 372 }
 373
 374 /**
 375  * cmm_sysfs_register - Register with sysfs
 376  *
 377  * Return value:
 378  *      0 on success / other on failure
 379  **/
 380 static int cmm_sysfs_register(struct device *dev)
 381 {
 382         int i, rc;
 383
 384         if ((rc = subsys_system_register(&cmm_subsys, NULL)))
 385                 return rc;
 386
 387         dev->id = 0;
 388         dev->bus = &cmm_subsys;
 389         dev->release = cmm_release_device;
 390
 391         if ((rc = device_register(dev)))
 392                 goto subsys_unregister;
 393
 394         for (i = 0; i < ARRAY_SIZE(cmm_attrs); i++) {
 395                 if ((rc = device_create_file(dev, cmm_attrs[i])))
 396                         goto fail;
 397         }
 398
 399         return 0;
 400
 401 fail:
 402         while (--i >= 0)
 403                 device_remove_file(dev, cmm_attrs[i]);
 404         device_unregister(dev);
 405 subsys_unregister:
 406         bus_unregister(&cmm_subsys);
 407         return rc;
 408 }
 409
 410 /**
 411  * cmm_unregister_sysfs - Unregister from sysfs
 412  *
 413  **/
 414 static void cmm_unregister_sysfs(struct device *dev)
 415 {
 416         int i;
 417
 418         for (i = 0; i < ARRAY_SIZE(cmm_attrs); i++)
 419                 device_remove_file(dev, cmm_attrs[i]);
 420         device_unregister(dev);
 421         bus_unregister(&cmm_subsys);
 422 }
 423
 424 /**
 425  * cmm_reboot_notifier - Make sure pages are not still marked as "loaned"
 426  *
 427  **/
 428 static int cmm_reboot_notifier(struct notifier_block *nb,
 429                                unsigned long action, void *unused)
 430 {
 431         if (action == SYS_RESTART) {
 432                 if (cmm_thread_ptr)
 433                         kthread_stop(cmm_thread_ptr);
 434                 cmm_thread_ptr = NULL;
 435                 cmm_free_pages(atomic_long_read(&loaned_pages));
 436         }
 437         return NOTIFY_DONE;
 438 }
 439
 440 static struct notifier_block cmm_reboot_nb = {
 441         .notifier_call = cmm_reboot_notifier,
 442 };
 443
 444 /**
 445  * cmm_memory_cb - Handle memory hotplug notifier calls
 446  * @self:       notifier block struct
 447  * @action:     action to take
 448  * @arg:        struct memory_notify data for handler
 449  *
 450  * Return value:
 451  *      NOTIFY_OK or notifier error based on subfunction return value
 452  *
 453  **/
 454 static int cmm_memory_cb(struct notifier_block *self,
 455                         unsigned long action, void *arg)
 456 {
 457         int ret = 0;
 458
 459         switch (action) {
 460         case MEM_GOING_OFFLINE:
 461                 mutex_lock(&hotplug_mutex);
 462                 hotplug_occurred = 1;
 463                 break;
 464         case MEM_OFFLINE:
 465         case MEM_CANCEL_OFFLINE:
 466                 mutex_unlock(&hotplug_mutex);
 467                 cmm_dbg("Memory offline operation complete.\n");
 468                 break;
 469         case MEM_GOING_ONLINE:
 470         case MEM_ONLINE:
 471         case MEM_CANCEL_ONLINE:
 472                 break;
 473         }
 474
 475         return notifier_from_errno(ret);
 476 }
 477
 478 static struct notifier_block cmm_mem_nb = {
 479         .notifier_call = cmm_memory_cb,
 480         .priority = CMM_MEM_HOTPLUG_PRI
 481 };
 482
 483 #ifdef CONFIG_BALLOON_COMPACTION
 484 static struct vfsmount *balloon_mnt;
 485
 486 static int cmm_init_fs_context(struct fs_context *fc)
 487 {
 488         return init_pseudo(fc, PPC_CMM_MAGIC) ? 0 : -ENOMEM;
 489 }
 490
 491 static struct file_system_type balloon_fs = {
 492         .name = "ppc-cmm",
 493         .init_fs_context = cmm_init_fs_context,
 494         .kill_sb = kill_anon_super,
 495 };
 496
 497 static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
 498                            struct page *newpage, struct page *page,
 499                            enum migrate_mode mode)
 500 {
 501         unsigned long flags;
 502
 503         /*
 504          * loan/"inflate" the newpage first.
 505          *
 506          * We might race against the cmm_thread who might discover after our
 507          * loan request that another page is to be unloaned. However, once
 508          * the cmm_thread runs again later, this error will automatically
 509          * be corrected.
 510          */
 511         if (plpar_page_set_loaned(newpage)) {
 512                 /* Unlikely, but possible. Tell the caller not to retry now. */
 513                 pr_err_ratelimited("%s: Cannot set page to loaned.", __func__);
 514                 return -EBUSY;
 515         }
 516
 517         /* balloon page list reference */
 518         get_page(newpage);
 519
 520         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 521         balloon_page_insert(b_dev_info, newpage);
 522         balloon_page_delete(page);
 523         b_dev_info->isolated_pages--;
 524         spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 525
 526         /*
 527          * activate/"deflate" the old page. We ignore any errors just like the
 528          * other callers.
 529          */
 530         plpar_page_set_active(page);
 531
 532         /* balloon page list reference */
 533         put_page(page);
 534
 535         return MIGRATEPAGE_SUCCESS;
 536 }
 537
 538 static int cmm_balloon_compaction_init(void)
 539 {
 540         int rc;
 541
 542         balloon_devinfo_init(&b_dev_info);
 543         b_dev_info.migratepage = cmm_migratepage;
 544
 545         balloon_mnt = kern_mount(&balloon_fs);
 546         if (IS_ERR(balloon_mnt)) {
 547                 rc = PTR_ERR(balloon_mnt);
 548                 balloon_mnt = NULL;
 549                 return rc;
 550         }
 551
 552         b_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
 553         if (IS_ERR(b_dev_info.inode)) {
 554                 rc = PTR_ERR(b_dev_info.inode);
 555                 b_dev_info.inode = NULL;
 556                 kern_unmount(balloon_mnt);
 557                 balloon_mnt = NULL;
 558                 return rc;
 559         }
 560
 561         b_dev_info.inode->i_mapping->a_ops = &balloon_aops;
 562         return 0;
 563 }
 564 static void cmm_balloon_compaction_deinit(void)
 565 {
 566         if (b_dev_info.inode)
 567                 iput(b_dev_info.inode);
 568         b_dev_info.inode = NULL;
 569         kern_unmount(balloon_mnt);
 570         balloon_mnt = NULL;
 571 }
 572 #else /* CONFIG_BALLOON_COMPACTION */
 573 static int cmm_balloon_compaction_init(void)
 574 {
 575         return 0;
 576 }
 577
 578 static void cmm_balloon_compaction_deinit(void)
 579 {
 580 }
 581 #endif /* CONFIG_BALLOON_COMPACTION */
 582
 583 /**
 584  * cmm_init - Module initialization
 585  *
 586  * Return value:
 587  *      0 on success / other on failure
 588  **/
 589 static int cmm_init(void)
 590 {
 591         int rc;
 592
 593         if (!firmware_has_feature(FW_FEATURE_CMO))
 594                 return -EOPNOTSUPP;
 595
 596         rc = cmm_balloon_compaction_init();
 597         if (rc)
 598                 return rc;
 599
 600         rc = register_oom_notifier(&cmm_oom_nb);
 601         if (rc < 0)
 602                 goto out_balloon_compaction;
 603
 604         if ((rc = register_reboot_notifier(&cmm_reboot_nb)))
 605                 goto out_oom_notifier;
 606
 607         if ((rc = cmm_sysfs_register(&cmm_dev)))
 608                 goto out_reboot_notifier;
 609
 610         rc = register_memory_notifier(&cmm_mem_nb);
 611         if (rc)
 612                 goto out_unregister_notifier;
 613
 614         if (cmm_disabled)
 615                 return 0;
 616
 617         cmm_thread_ptr = kthread_run(cmm_thread, NULL, "cmmthread");
 618         if (IS_ERR(cmm_thread_ptr)) {
 619                 rc = PTR_ERR(cmm_thread_ptr);
 620                 goto out_unregister_notifier;
 621         }
 622
 623         return 0;
 624 out_unregister_notifier:
 625         unregister_memory_notifier(&cmm_mem_nb);
 626         cmm_unregister_sysfs(&cmm_dev);
 627 out_reboot_notifier:
 628         unregister_reboot_notifier(&cmm_reboot_nb);
 629 out_oom_notifier:
 630         unregister_oom_notifier(&cmm_oom_nb);
 631 out_balloon_compaction:
 632         cmm_balloon_compaction_deinit();
 633         return rc;
 634 }
 635
 636 /**
 637  * cmm_exit - Module exit
 638  *
 639  * Return value:
 640  *      nothing
 641  **/
 642 static void cmm_exit(void)
 643 {
 644         if (cmm_thread_ptr)
 645                 kthread_stop(cmm_thread_ptr);
 646         unregister_oom_notifier(&cmm_oom_nb);
 647         unregister_reboot_notifier(&cmm_reboot_nb);
 648         unregister_memory_notifier(&cmm_mem_nb);
 649         cmm_free_pages(atomic_long_read(&loaned_pages));
 650         cmm_unregister_sysfs(&cmm_dev);
 651         cmm_balloon_compaction_deinit();
 652 }
 653
 654 /**
 655  * cmm_set_disable - Disable/Enable CMM
 656  *
 657  * Return value:
 658  *      0 on success / other on failure
 659  **/
 660 static int cmm_set_disable(const char *val, const struct kernel_param *kp)
 661 {
 662         int disable = simple_strtoul(val, NULL, 10);
 663
 664         if (disable != 0 && disable != 1)
 665                 return -EINVAL;
 666
 667         if (disable && !cmm_disabled) {
 668                 if (cmm_thread_ptr)
 669                         kthread_stop(cmm_thread_ptr);
 670                 cmm_thread_ptr = NULL;
 671                 cmm_free_pages(atomic_long_read(&loaned_pages));
 672         } else if (!disable && cmm_disabled) {
 673                 cmm_thread_ptr = kthread_run(cmm_thread, NULL, "cmmthread");
 674                 if (IS_ERR(cmm_thread_ptr))
 675                         return PTR_ERR(cmm_thread_ptr);
 676         }
 677
 678         cmm_disabled = disable;
 679         return 0;
 680 }
 681
 682 module_param_call(disable, cmm_set_disable, param_get_uint,
 683                   &cmm_disabled, 0644);
 684 MODULE_PARM_DESC(disable, "Disable CMM. Set to 1 to disable. "
 685                  "[Default=" __stringify(CMM_DISABLE) "]");
 686
 687 module_init(cmm_init);
 688 module_exit(cmm_exit);