mm/highmem.c

   1 /*
   2  * High memory handling common code and variables.
   3  *
   4  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
   5  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
   6  *
   7  *
   8  * Redesigned the x86 32-bit VM architecture to deal with
   9  * 64-bit physical space. With current x86 CPUs this
  10  * means up to 64 Gigabytes physical RAM.
  11  *
  12  * Rewrote high memory support to move the page cache into
  13  * high memory. Implemented permanent (schedulable) kmaps
  14  * based on Linus' idea.
  15  *
  16  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  17  */
  18
  19 #include <linux/mm.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/highmem.h>
  22 #include <linux/swap.h>
  23 #include <linux/slab.h>
  24
  25 unsigned long highmem_mapnr;
  26
  27 /*
  28  * Take one locked page, return another low-memory locked page.
  29  */
  30 struct page * prepare_highmem_swapout(struct page * page)
  31 {
  32         struct page *new_page;
  33         unsigned long regular_page;
  34         unsigned long vaddr;
  35         /*
  36          * If this is a highmem page so it can't be swapped out directly
  37          * otherwise the b_data buffer addresses will break
  38          * the lowlevel device drivers.
  39          */
  40         if (!PageHighMem(page))
  41                 return page;
  42
  43         /*
  44          * Here we break the page lock, and we split the
  45          * dirty page into two. We can unlock the old page,
  46          * and we'll now have two of them. Too bad, it would
  47          * have been nice to continue to potentially share
  48          * across a fork().
  49          */
  50         UnlockPage(page);
  51         regular_page = __get_free_page(GFP_ATOMIC);
  52         if (!regular_page)
  53                 return NULL;
  54
  55         vaddr = kmap(page);
  56         copy_page((void *)regular_page, (void *)vaddr);
  57         kunmap(page);
  58
  59         /*
  60          * ok, we can just forget about our highmem page since
  61          * we stored its data into the new regular_page.
  62          */
  63         page_cache_release(page);
  64         new_page = mem_map + MAP_NR(regular_page);
  65         LockPage(new_page);
  66         return new_page;
  67 }
  68
  69 struct page * replace_with_highmem(struct page * page)
  70 {
  71         struct page *highpage;
  72         unsigned long vaddr;
  73
  74         if (PageHighMem(page) || !nr_free_highpages())
  75                 return page;
  76
  77         highpage = alloc_page(GFP_ATOMIC|__GFP_HIGHMEM);
  78         if (!highpage)
  79                 return page;
  80         if (!PageHighMem(highpage)) {
  81                 page_cache_release(highpage);
  82                 return page;
  83         }
  84
  85         vaddr = kmap(highpage);
  86         copy_page((void *)vaddr, (void *)page_address(page));
  87         kunmap(highpage);
  88
  89         if (page->mapping)
  90                 BUG();
  91
  92         /*
  93          * We can just forget the old page since
  94          * we stored its data into the new highmem-page.
  95          */
  96         page_cache_release(page);
  97
  98         return highpage;
  99 }
 100
 101 /*
 102  * Virtual_count is not a pure "count".
 103  *  0 means that it is not mapped, and has not been mapped
 104  *    since a TLB flush - it is usable.
 105  *  1 means that there are no users, but it has been mapped
 106  *    since the last TLB flush - so we can't use it.
 107  *  n means that there are (n-1) current users of it.
 108  */
 109 static int pkmap_count[LAST_PKMAP];
 110 static unsigned int last_pkmap_nr;
 111 static spinlock_t kmap_lock = SPIN_LOCK_UNLOCKED;
 112
 113 pte_t * pkmap_page_table;
 114
 115 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
 116
 117 static void flush_all_zero_pkmaps(void)
 118 {
 119         int i;
 120
 121         flush_cache_all();
 122
 123         for (i = 0; i < LAST_PKMAP; i++) {
 124                 struct page *page;
 125                 pte_t pte;
 126                 /*
 127                  * zero means we don't have anything to do,
 128                  * >1 means that it is still in use. Only
 129                  * a count of 1 means that it is free but
 130                  * needs to be unmapped
 131                  */
 132                 if (pkmap_count[i] != 1)
 133                         continue;
 134                 pkmap_count[i] = 0;
 135                 pte = pkmap_page_table[i];
 136                 if (pte_none(pte))
 137                         BUG();
 138                 pte_clear(pkmap_page_table+i);
 139                 page = pte_page(pte);
 140                 page->virtual = 0;
 141         }
 142         flush_tlb_all();
 143 }
 144
 145 static inline unsigned long map_new_virtual(struct page *page)
 146 {
 147         unsigned long vaddr;
 148         int count;
 149
 150 start:
 151         count = LAST_PKMAP;
 152         /* Find an empty entry */
 153         for (;;) {
 154                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
 155                 if (!last_pkmap_nr) {
 156                         flush_all_zero_pkmaps();
 157                         count = LAST_PKMAP;
 158                 }
 159                 if (!pkmap_count[last_pkmap_nr])
 160                         break;  /* Found a usable entry */
 161                 if (--count)
 162                         continue;
 163
 164                 /*
 165                  * Sleep for somebody else to unmap their entries
 166                  */
 167                 {
 168                         DECLARE_WAITQUEUE(wait, current);
 169
 170                         current->state = TASK_UNINTERRUPTIBLE;
 171                         add_wait_queue(&pkmap_map_wait, &wait);
 172                         spin_unlock(&kmap_lock);
 173                         schedule();
 174                         remove_wait_queue(&pkmap_map_wait, &wait);
 175                         spin_lock(&kmap_lock);
 176
 177                         /* Somebody else might have mapped it while we slept */
 178                         if (page->virtual)
 179                                 return page->virtual;
 180
 181                         /* Re-start */
 182                         goto start;
 183                 }
 184         }
 185         vaddr = PKMAP_ADDR(last_pkmap_nr);
 186         set_pte(pkmap_page_table + last_pkmap_nr, mk_pte(page, kmap_prot));
 187
 188         pkmap_count[last_pkmap_nr] = 1;
 189         page->virtual = vaddr;
 190
 191         return vaddr;
 192 }
 193
 194 unsigned long kmap_high(struct page *page)
 195 {
 196         unsigned long vaddr;
 197
 198         /*
 199          * For highmem pages, we can't trust "virtual" until
 200          * after we have the lock.
 201          *
 202          * We cannot call this from interrupts, as it may block
 203          */
 204         spin_lock(&kmap_lock);
 205         vaddr = page->virtual;
 206         if (!vaddr)
 207                 vaddr = map_new_virtual(page);
 208         pkmap_count[PKMAP_NR(vaddr)]++;
 209         if (pkmap_count[PKMAP_NR(vaddr)] < 2)
 210                 BUG();
 211         spin_unlock(&kmap_lock);
 212         return vaddr;
 213 }
 214
 215 void kunmap_high(struct page *page)
 216 {
 217         unsigned long vaddr;
 218         unsigned long nr;
 219
 220         spin_lock(&kmap_lock);
 221         vaddr = page->virtual;
 222         if (!vaddr)
 223                 BUG();
 224         nr = PKMAP_NR(vaddr);
 225
 226         /*
 227          * A count must never go down to zero
 228          * without a TLB flush!
 229          */
 230         switch (--pkmap_count[nr]) {
 231         case 0:
 232                 BUG();
 233         case 1:
 234                 wake_up(&pkmap_map_wait);
 235         }
 236         spin_unlock(&kmap_lock);
 237 }
 238
 239 /*
 240  * Simple bounce buffer support for highmem pages.
 241  * This will be moved to the block layer in 2.5.
 242  */
 243
 244 static inline void copy_from_high_bh (struct buffer_head *to,
 245                          struct buffer_head *from)
 246 {
 247         struct page *p_from;
 248         unsigned long vfrom;
 249         unsigned long flags;
 250
 251         p_from = from->b_page;
 252
 253         /*
 254          * Since this can be executed from IRQ context, reentrance
 255          * on the same CPU must be avoided:
 256          */
 257         __save_flags(flags);
 258         __cli();
 259         vfrom = kmap_atomic(p_from, KM_BOUNCE_WRITE);
 260         memcpy(to->b_data, (char *)vfrom + bh_offset(from), to->b_size);
 261         kunmap_atomic(vfrom, KM_BOUNCE_WRITE);
 262         __restore_flags(flags);
 263 }
 264
 265 static inline void copy_to_high_bh_irq (struct buffer_head *to,
 266                          struct buffer_head *from)
 267 {
 268         struct page *p_to;
 269         unsigned long vto;
 270         unsigned long flags;
 271
 272         p_to = to->b_page;
 273         __save_flags(flags);
 274         __cli();
 275         vto = kmap_atomic(p_to, KM_BOUNCE_READ);
 276         memcpy((char *)vto + bh_offset(to), from->b_data, to->b_size);
 277         kunmap_atomic(vto, KM_BOUNCE_READ);
 278         __restore_flags(flags);
 279 }
 280
 281 static inline void bounce_end_io (struct buffer_head *bh, int uptodate)
 282 {
 283         struct buffer_head *bh_orig = (struct buffer_head *)(bh->b_private);
 284
 285         bh_orig->b_end_io(bh_orig, uptodate);
 286         __free_page(bh->b_page);
 287         kmem_cache_free(bh_cachep, bh);
 288 }
 289
 290 static void bounce_end_io_write (struct buffer_head *bh, int uptodate)
 291 {
 292         bounce_end_io(bh, uptodate);
 293 }
 294
 295 static void bounce_end_io_read (struct buffer_head *bh, int uptodate)
 296 {
 297         struct buffer_head *bh_orig = (struct buffer_head *)(bh->b_private);
 298
 299         if (uptodate)
 300                 copy_to_high_bh_irq(bh_orig, bh);
 301         bounce_end_io(bh, uptodate);
 302 }
 303
 304 struct buffer_head * create_bounce(int rw, struct buffer_head * bh_orig)
 305 {
 306         struct page *page;
 307         struct buffer_head *bh;
 308
 309         if (!PageHighMem(bh_orig->b_page))
 310                 return bh_orig;
 311
 312 repeat_bh:
 313         bh = kmem_cache_alloc(bh_cachep, SLAB_BUFFER);
 314         if (!bh) {
 315                 wakeup_bdflush(1);
 316                 current->policy |= SCHED_YIELD;
 317                 schedule();
 318                 goto repeat_bh;
 319         }
 320         /*
 321          * This is wasteful for 1k buffers, but this is a stopgap measure
 322          * and we are being ineffective anyway. This approach simplifies
 323          * things immensly. On boxes with more than 4GB RAM this should
 324          * not be an issue anyway.
 325          */
 326 repeat_page:
 327         page = alloc_page(GFP_BUFFER);
 328         if (!page) {
 329                 wakeup_bdflush(1);
 330                 current->policy |= SCHED_YIELD;
 331                 schedule();
 332                 goto repeat_page;
 333         }
 334         set_bh_page(bh, page, 0);
 335
 336         bh->b_next = NULL;
 337         bh->b_blocknr = bh_orig->b_blocknr;
 338         bh->b_size = bh_orig->b_size;
 339         bh->b_list = -1;
 340         bh->b_dev = bh_orig->b_dev;
 341         bh->b_count = bh_orig->b_count;
 342         bh->b_rdev = bh_orig->b_rdev;
 343         bh->b_state = bh_orig->b_state;
 344         bh->b_flushtime = 0;
 345         bh->b_next_free = NULL;
 346         bh->b_prev_free = NULL;
 347         /* bh->b_this_page */
 348         bh->b_reqnext = NULL;
 349         bh->b_pprev = NULL;
 350         /* bh->b_page */
 351         if (rw == WRITE) {
 352                 bh->b_end_io = bounce_end_io_write;
 353                 copy_from_high_bh(bh, bh_orig);
 354         } else
 355                 bh->b_end_io = bounce_end_io_read;
 356         bh->b_private = (void *)bh_orig;
 357         bh->b_rsector = bh_orig->b_rsector;
 358         memset(&bh->b_wait, -1, sizeof(bh->b_wait));
 359
 360         return bh;
 361 }
 362