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  * Redesigned the x86 32-bit VM architecture to deal with
   8  * 64-bit physical space. With current x86 CPUs this
   9  * means up to 64 Gigabytes physical RAM.
  10  *
  11  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  12  */
  13
  14 #include <linux/mm.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/highmem.h>
  17
  18 unsigned long highmem_mapnr;
  19 unsigned long nr_free_highpages = 0;
  20
  21 struct page * prepare_highmem_swapout(struct page * page)
  22 {
  23         unsigned long regular_page;
  24         unsigned long vaddr;
  25         /*
  26          * If this is a highmem page so it can't be swapped out directly
  27          * otherwise the b_data buffer addresses will break
  28          * the lowlevel device drivers.
  29          */
  30         if (!PageHighMem(page))
  31                 return page;
  32
  33         regular_page = __get_free_page(GFP_ATOMIC);
  34         if (!regular_page)
  35                 return NULL;
  36
  37         vaddr = kmap(page, KM_READ);
  38         copy_page((void *)regular_page, (void *)vaddr);
  39         kunmap(vaddr, KM_READ);
  40
  41         /*
  42          * ok, we can just forget about our highmem page since
  43          * we stored its data into the new regular_page.
  44          */
  45         __free_page(page);
  46
  47         return mem_map + MAP_NR(regular_page);
  48 }
  49
  50 struct page * replace_with_highmem(struct page * page)
  51 {
  52         struct page *highpage;
  53         unsigned long vaddr;
  54
  55         if (PageHighMem(page) || !nr_free_highpages)
  56                 return page;
  57
  58         highpage = get_free_highpage(GFP_ATOMIC|__GFP_HIGHMEM);
  59         if (!highpage)
  60                 return page;
  61         if (!PageHighMem(highpage)) {
  62                 __free_page(highpage);
  63                 return page;
  64         }
  65
  66         vaddr = kmap(highpage, KM_WRITE);
  67         copy_page((void *)vaddr, (void *)page_address(page));
  68         kunmap(vaddr, KM_WRITE);
  69
  70         /* Preserve the caching of the swap_entry. */
  71         highpage->pg_offset = page->pg_offset;
  72         highpage->mapping = page->mapping;
  73
  74         /*
  75          * We can just forget the old page since
  76          * we stored its data into the new highmem-page.
  77          */
  78         __free_page(page);
  79
  80         return highpage;
  81 }