mm/page_reporting.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/mm.h>
   3 #include <linux/mmzone.h>
   4 #include <linux/page_reporting.h>
   5 #include <linux/gfp.h>
   6 #include <linux/export.h>
   7 #include <linux/delay.h>
   8 #include <linux/scatterlist.h>
   9
  10 #include "page_reporting.h"
  11 #include "internal.h"
  12
  13 #define PAGE_REPORTING_DELAY    (2 * HZ)
  14 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
  15
  16 enum {
  17         PAGE_REPORTING_IDLE = 0,
  18         PAGE_REPORTING_REQUESTED,
  19         PAGE_REPORTING_ACTIVE
  20 };
  21
  22 /* request page reporting */
  23 static void
  24 __page_reporting_request(struct page_reporting_dev_info *prdev)
  25 {
  26         unsigned int state;
  27
  28         /* Check to see if we are in desired state */
  29         state = atomic_read(&prdev->state);
  30         if (state == PAGE_REPORTING_REQUESTED)
  31                 return;
  32
  33         /*
  34          *  If reporting is already active there is nothing we need to do.
  35          *  Test against 0 as that represents PAGE_REPORTING_IDLE.
  36          */
  37         state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
  38         if (state != PAGE_REPORTING_IDLE)
  39                 return;
  40
  41         /*
  42          * Delay the start of work to allow a sizable queue to build. For
  43          * now we are limiting this to running no more than once every
  44          * couple of seconds.
  45          */
  46         schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
  47 }
  48
  49 /* notify prdev of free page reporting request */
  50 void __page_reporting_notify(void)
  51 {
  52         struct page_reporting_dev_info *prdev;
  53
  54         /*
  55          * We use RCU to protect the pr_dev_info pointer. In almost all
  56          * cases this should be present, however in the unlikely case of
  57          * a shutdown this will be NULL and we should exit.
  58          */
  59         rcu_read_lock();
  60         prdev = rcu_dereference(pr_dev_info);
  61         if (likely(prdev))
  62                 __page_reporting_request(prdev);
  63
  64         rcu_read_unlock();
  65 }
  66
  67 static void
  68 page_reporting_drain(struct page_reporting_dev_info *prdev,
  69                      struct scatterlist *sgl, unsigned int nents, bool reported)
  70 {
  71         struct scatterlist *sg = sgl;
  72
  73         /*
  74          * Drain the now reported pages back into their respective
  75          * free lists/areas. We assume at least one page is populated.
  76          */
  77         do {
  78                 struct page *page = sg_page(sg);
  79                 int mt = get_pageblock_migratetype(page);
  80                 unsigned int order = get_order(sg->length);
  81
  82                 __putback_isolated_page(page, order, mt);
  83
  84                 /* If the pages were not reported due to error skip flagging */
  85                 if (!reported)
  86                         continue;
  87
  88                 /*
  89                  * If page was not comingled with another page we can
  90                  * consider the result to be "reported" since the page
  91                  * hasn't been modified, otherwise we will need to
  92                  * report on the new larger page when we make our way
  93                  * up to that higher order.
  94                  */
  95                 if (PageBuddy(page) && buddy_order(page) == order)
  96                         __SetPageReported(page);
  97         } while ((sg = sg_next(sg)));
  98
  99         /* reinitialize scatterlist now that it is empty */
 100         sg_init_table(sgl, nents);
 101 }
 102
 103 /*
 104  * The page reporting cycle consists of 4 stages, fill, report, drain, and
 105  * idle. We will cycle through the first 3 stages until we cannot obtain a
 106  * full scatterlist of pages, in that case we will switch to idle.
 107  */
 108 static int
 109 page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 110                      unsigned int order, unsigned int mt,
 111                      struct scatterlist *sgl, unsigned int *offset)
 112 {
 113         struct free_area *area = &zone->free_area[order];
 114         struct list_head *list = &area->free_list[mt];
 115         unsigned int page_len = PAGE_SIZE << order;
 116         struct page *page, *next;
 117         long budget;
 118         int err = 0;
 119
 120         /*
 121          * Perform early check, if free area is empty there is
 122          * nothing to process so we can skip this free_list.
 123          */
 124         if (list_empty(list))
 125                 return err;
 126
 127         spin_lock_irq(&zone->lock);
 128
 129         /*
 130          * Limit how many calls we will be making to the page reporting
 131          * device for this list. By doing this we avoid processing any
 132          * given list for too long.
 133          *
 134          * The current value used allows us enough calls to process over a
 135          * sixteenth of the current list plus one additional call to handle
 136          * any pages that may have already been present from the previous
 137          * list processed. This should result in us reporting all pages on
 138          * an idle system in about 30 seconds.
 139          *
 140          * The division here should be cheap since PAGE_REPORTING_CAPACITY
 141          * should always be a power of 2.
 142          */
 143         budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);
 144
 145         /* loop through free list adding unreported pages to sg list */
 146         list_for_each_entry_safe(page, next, list, lru) {
 147                 /* We are going to skip over the reported pages. */
 148                 if (PageReported(page))
 149                         continue;
 150
 151                 /*
 152                  * If we fully consumed our budget then update our
 153                  * state to indicate that we are requesting additional
 154                  * processing and exit this list.
 155                  */
 156                 if (budget < 0) {
 157                         atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
 158                         next = page;
 159                         break;
 160                 }
 161
 162                 /* Attempt to pull page from list and place in scatterlist */
 163                 if (*offset) {
 164                         if (!__isolate_free_page(page, order)) {
 165                                 next = page;
 166                                 break;
 167                         }
 168
 169                         /* Add page to scatter list */
 170                         --(*offset);
 171                         sg_set_page(&sgl[*offset], page, page_len, 0);
 172
 173                         continue;
 174                 }
 175
 176                 /*
 177                  * Make the first non-reported page in the free list
 178                  * the new head of the free list before we release the
 179                  * zone lock.
 180                  */
 181                 if (!list_is_first(&page->lru, list))
 182                         list_rotate_to_front(&page->lru, list);
 183
 184                 /* release lock before waiting on report processing */
 185                 spin_unlock_irq(&zone->lock);
 186
 187                 /* begin processing pages in local list */
 188                 err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
 189
 190                 /* reset offset since the full list was reported */
 191                 *offset = PAGE_REPORTING_CAPACITY;
 192
 193                 /* update budget to reflect call to report function */
 194                 budget--;
 195
 196                 /* reacquire zone lock and resume processing */
 197                 spin_lock_irq(&zone->lock);
 198
 199                 /* flush reported pages from the sg list */
 200                 page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
 201
 202                 /*
 203                  * Reset next to first entry, the old next isn't valid
 204                  * since we dropped the lock to report the pages
 205                  */
 206                 next = list_first_entry(list, struct page, lru);
 207
 208                 /* exit on error */
 209                 if (err)
 210                         break;
 211         }
 212
 213         /* Rotate any leftover pages to the head of the freelist */
 214         if (&next->lru != list && !list_is_first(&next->lru, list))
 215                 list_rotate_to_front(&next->lru, list);
 216
 217         spin_unlock_irq(&zone->lock);
 218
 219         return err;
 220 }
 221
 222 static int
 223 page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 224                             struct scatterlist *sgl, struct zone *zone)
 225 {
 226         unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
 227         unsigned long watermark;
 228         int err = 0;
 229
 230         /* Generate minimum watermark to be able to guarantee progress */
 231         watermark = low_wmark_pages(zone) +
 232                     (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
 233
 234         /*
 235          * Cancel request if insufficient free memory or if we failed
 236          * to allocate page reporting statistics for the zone.
 237          */
 238         if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
 239                 return err;
 240
 241         /* Process each free list starting from lowest order/mt */
 242         for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
 243                 for (mt = 0; mt < MIGRATE_TYPES; mt++) {
 244                         /* We do not pull pages from the isolate free list */
 245                         if (is_migrate_isolate(mt))
 246                                 continue;
 247
 248                         err = page_reporting_cycle(prdev, zone, order, mt,
 249                                                    sgl, &offset);
 250                         if (err)
 251                                 return err;
 252                 }
 253         }
 254
 255         /* report the leftover pages before going idle */
 256         leftover = PAGE_REPORTING_CAPACITY - offset;
 257         if (leftover) {
 258                 sgl = &sgl[offset];
 259                 err = prdev->report(prdev, sgl, leftover);
 260
 261                 /* flush any remaining pages out from the last report */
 262                 spin_lock_irq(&zone->lock);
 263                 page_reporting_drain(prdev, sgl, leftover, !err);
 264                 spin_unlock_irq(&zone->lock);
 265         }
 266
 267         return err;
 268 }
 269
 270 static void page_reporting_process(struct work_struct *work)
 271 {
 272         struct delayed_work *d_work = to_delayed_work(work);
 273         struct page_reporting_dev_info *prdev =
 274                 container_of(d_work, struct page_reporting_dev_info, work);
 275         int err = 0, state = PAGE_REPORTING_ACTIVE;
 276         struct scatterlist *sgl;
 277         struct zone *zone;
 278
 279         /*
 280          * Change the state to "Active" so that we can track if there is
 281          * anyone requests page reporting after we complete our pass. If
 282          * the state is not altered by the end of the pass we will switch
 283          * to idle and quit scheduling reporting runs.
 284          */
 285         atomic_set(&prdev->state, state);
 286
 287         /* allocate scatterlist to store pages being reported on */
 288         sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
 289         if (!sgl)
 290                 goto err_out;
 291
 292         sg_init_table(sgl, PAGE_REPORTING_CAPACITY);
 293
 294         for_each_zone(zone) {
 295                 err = page_reporting_process_zone(prdev, sgl, zone);
 296                 if (err)
 297                         break;
 298         }
 299
 300         kfree(sgl);
 301 err_out:
 302         /*
 303          * If the state has reverted back to requested then there may be
 304          * additional pages to be processed. We will defer for 2s to allow
 305          * more pages to accumulate.
 306          */
 307         state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
 308         if (state == PAGE_REPORTING_REQUESTED)
 309                 schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
 310 }
 311
 312 static DEFINE_MUTEX(page_reporting_mutex);
 313 DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
 314
 315 int page_reporting_register(struct page_reporting_dev_info *prdev)
 316 {
 317         int err = 0;
 318
 319         mutex_lock(&page_reporting_mutex);
 320
 321         /* nothing to do if already in use */
 322         if (rcu_access_pointer(pr_dev_info)) {
 323                 err = -EBUSY;
 324                 goto err_out;
 325         }
 326
 327         /* initialize state and work structures */
 328         atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
 329         INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
 330
 331         /* Begin initial flush of zones */
 332         __page_reporting_request(prdev);
 333
 334         /* Assign device to allow notifications */
 335         rcu_assign_pointer(pr_dev_info, prdev);
 336
 337         /* enable page reporting notification */
 338         if (!static_key_enabled(&page_reporting_enabled)) {
 339                 static_branch_enable(&page_reporting_enabled);
 340                 pr_info("Free page reporting enabled\n");
 341         }
 342 err_out:
 343         mutex_unlock(&page_reporting_mutex);
 344
 345         return err;
 346 }
 347 EXPORT_SYMBOL_GPL(page_reporting_register);
 348
 349 void page_reporting_unregister(struct page_reporting_dev_info *prdev)
 350 {
 351         mutex_lock(&page_reporting_mutex);
 352
 353         if (rcu_access_pointer(pr_dev_info) == prdev) {
 354                 /* Disable page reporting notification */
 355                 RCU_INIT_POINTER(pr_dev_info, NULL);
 356                 synchronize_rcu();
 357
 358                 /* Flush any existing work, and lock it out */
 359                 cancel_delayed_work_sync(&prdev->work);
 360         }
 361
 362         mutex_unlock(&page_reporting_mutex);
 363 }
 364 EXPORT_SYMBOL_GPL(page_reporting_unregister);