FreeBSD/Linux Kernel Cross Reference
sys/mm/memory.c

     /*
      *  linux/mm/memory.c
      *
      *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
      */
     
     /*
      * demand-loading started 01.12.91 - seems it is high on the list of
      * things wanted, and it should be easy to implement. - Linus
     */
    
    /*
     * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
     * pages started 02.12.91, seems to work. - Linus.
     *
     * Tested sharing by executing about 30 /bin/sh: under the old kernel it
     * would have taken more than the 6M I have free, but it worked well as
     * far as I could see.
     *
     * Also corrected some "invalidate()"s - I wasn't doing enough of them.
     */
    
    /*
     * Real VM (paging to/from disk) started 18.12.91. Much more work and
     * thought has to go into this. Oh, well..
     * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
     *              Found it. Everything seems to work now.
     * 20.12.91  -  Ok, making the swap-device changeable like the root.
     */
    
    /*
     * 05.04.94  -  Multi-page memory management added for v1.1.
     *              Idea by Alex Bligh (alex@cconcepts.co.uk)
     *
     * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
     *              (Gerhard.Wichert@pdb.siemens.de)
     */
    
    #include <linux/mm.h>
    #include <linux/mman.h>
    #include <linux/swap.h>
    #include <linux/smp_lock.h>
    #include <linux/swapctl.h>
    #include <linux/iobuf.h>
    #include <linux/highmem.h>
    #include <linux/pagemap.h>
    #include <linux/module.h>
    
    #include <asm/pgalloc.h>
    #include <asm/uaccess.h>
    #include <asm/tlb.h>
    
    unsigned long max_mapnr;
    unsigned long num_physpages;
    unsigned long num_mappedpages;
    void * high_memory;
    struct page *highmem_start_page;
    
    /*
     * We special-case the C-O-W ZERO_PAGE, because it's such
     * a common occurrence (no need to read the page to know
     * that it's zero - better for the cache and memory subsystem).
     */
    static inline void copy_cow_page(struct page * from, struct page * to, unsigned long address)
    {
            if (from == ZERO_PAGE(address)) {
                    clear_user_highpage(to, address);
                    return;
            }
            copy_user_highpage(to, from, address);
    }
    
    mem_map_t * mem_map;
    
    /*
     * Called by TLB shootdown 
     */
    void __free_pte(pte_t pte)
    {
            struct page *page = pte_page(pte);
            if ((!VALID_PAGE(page)) || PageReserved(page))
                    return;
            if (pte_dirty(pte))
                    set_page_dirty(page);           
            free_page_and_swap_cache(page);
    }
    
    
    /*
     * Note: this doesn't free the actual pages themselves. That
     * has been handled earlier when unmapping all the memory regions.
     */
    static inline void free_one_pmd(pmd_t * dir)
    {
            pte_t * pte;
    
            if (pmd_none(*dir))
                    return;
            if (pmd_bad(*dir)) {
                   pmd_ERROR(*dir);
                   pmd_clear(dir);
                   return;
           }
           pte = pte_offset(dir, 0);
           pmd_clear(dir);
           pte_free(pte);
   }
   
   static inline void free_one_pgd(pgd_t * dir)
   {
           int j;
           pmd_t * pmd;
   
           if (pgd_none(*dir))
                   return;
           if (pgd_bad(*dir)) {
                   pgd_ERROR(*dir);
                   pgd_clear(dir);
                   return;
           }
           pmd = pmd_offset(dir, 0);
           pgd_clear(dir);
           for (j = 0; j < PTRS_PER_PMD ; j++) {
                   prefetchw(pmd+j+(PREFETCH_STRIDE/16));
                   free_one_pmd(pmd+j);
           }
           pmd_free(pmd);
   }
   
   /* Low and high watermarks for page table cache.
      The system should try to have pgt_water[0] <= cache elements <= pgt_water[1]
    */
   int pgt_cache_water[2] = { 25, 50 };
   
   /* Returns the number of pages freed */
   int check_pgt_cache(void)
   {
           return do_check_pgt_cache(pgt_cache_water[0], pgt_cache_water[1]);
   }
   
   
   /*
    * This function clears all user-level page tables of a process - this
    * is needed by execve(), so that old pages aren't in the way.
    */
   void clear_page_tables(struct mm_struct *mm, unsigned long first, int nr)
   {
           pgd_t * page_dir = mm->pgd;
   
           spin_lock(&mm->page_table_lock);
           page_dir += first;
           do {
                   free_one_pgd(page_dir);
                   page_dir++;
           } while (--nr);
           spin_unlock(&mm->page_table_lock);
   
           /* keep the page table cache within bounds */
           check_pgt_cache();
   }
   
   #define PTE_TABLE_MASK  ((PTRS_PER_PTE-1) * sizeof(pte_t))
   #define PMD_TABLE_MASK  ((PTRS_PER_PMD-1) * sizeof(pmd_t))
   
   /*
    * copy one vm_area from one task to the other. Assumes the page tables
    * already present in the new task to be cleared in the whole range
    * covered by this vma.
    *
    * 08Jan98 Merged into one routine from several inline routines to reduce
    *         variable count and make things faster. -jj
    *
    * dst->page_table_lock is held on entry and exit,
    * but may be dropped within pmd_alloc() and pte_alloc().
    */
   int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
                           struct vm_area_struct *vma)
   {
           pgd_t * src_pgd, * dst_pgd;
           unsigned long address = vma->vm_start;
           unsigned long end = vma->vm_end;
           unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
   
           src_pgd = pgd_offset(src, address)-1;
           dst_pgd = pgd_offset(dst, address)-1;
   
           for (;;) {
                   pmd_t * src_pmd, * dst_pmd;
   
                   src_pgd++; dst_pgd++;
                   
                   /* copy_pmd_range */
                   
                   if (pgd_none(*src_pgd))
                           goto skip_copy_pmd_range;
                   if (pgd_bad(*src_pgd)) {
                           pgd_ERROR(*src_pgd);
                           pgd_clear(src_pgd);
   skip_copy_pmd_range:    address = (address + PGDIR_SIZE) & PGDIR_MASK;
                           if (!address || (address >= end))
                                   goto out;
                           continue;
                   }
   
                   src_pmd = pmd_offset(src_pgd, address);
                   dst_pmd = pmd_alloc(dst, dst_pgd, address);
                   if (!dst_pmd)
                           goto nomem;
   
                   do {
                           pte_t * src_pte, * dst_pte;
                   
                           /* copy_pte_range */
                   
                           if (pmd_none(*src_pmd))
                                   goto skip_copy_pte_range;
                           if (pmd_bad(*src_pmd)) {
                                   pmd_ERROR(*src_pmd);
                                   pmd_clear(src_pmd);
   skip_copy_pte_range:            address = (address + PMD_SIZE) & PMD_MASK;
                                   if (address >= end)
                                           goto out;
                                   goto cont_copy_pmd_range;
                           }
   
                           src_pte = pte_offset(src_pmd, address);
                           dst_pte = pte_alloc(dst, dst_pmd, address);
                           if (!dst_pte)
                                   goto nomem;
   
                           spin_lock(&src->page_table_lock);                       
                           do {
                                   pte_t pte = *src_pte;
                                   struct page *ptepage;
                                   
                                   /* copy_one_pte */
   
                                   if (pte_none(pte))
                                           goto cont_copy_pte_range_noset;
                                   if (!pte_present(pte)) {
                                           swap_duplicate(pte_to_swp_entry(pte));
                                           goto cont_copy_pte_range;
                                   }
                                   ptepage = pte_page(pte);
                                   if ((!VALID_PAGE(ptepage)) || 
                                       PageReserved(ptepage))
                                           goto cont_copy_pte_range;
   
                                   /* If it's a COW mapping, write protect it both in the parent and the child */
                                   if (cow && pte_write(pte)) {
                                           ptep_set_wrprotect(src_pte);
                                           pte = *src_pte;
                                   }
   
                                   /* If it's a shared mapping, mark it clean in the child */
                                   if (vma->vm_flags & VM_SHARED)
                                           pte = pte_mkclean(pte);
                                   pte = pte_mkold(pte);
                                   get_page(ptepage);
                                   dst->rss++;
   
   cont_copy_pte_range:            set_pte(dst_pte, pte);
   cont_copy_pte_range_noset:      address += PAGE_SIZE;
                                   if (address >= end)
                                           goto out_unlock;
                                   src_pte++;
                                   dst_pte++;
                           } while ((unsigned long)src_pte & PTE_TABLE_MASK);
                           spin_unlock(&src->page_table_lock);
                   
   cont_copy_pmd_range:    src_pmd++;
                           dst_pmd++;
                   } while ((unsigned long)src_pmd & PMD_TABLE_MASK);
           }
   out_unlock:
           spin_unlock(&src->page_table_lock);
   out:
           return 0;
   nomem:
           return -ENOMEM;
   }
   
   /*
    * Return indicates whether a page was freed so caller can adjust rss
    */
   static inline void forget_pte(pte_t page)
   {
           if (!pte_none(page)) {
                   printk("forget_pte: old mapping existed!\n");
                   BUG();
           }
   }
   
   static inline int zap_pte_range(mmu_gather_t *tlb, pmd_t * pmd, unsigned long address, unsigned long size)
   {
           unsigned long offset;
           pte_t * ptep;
           int freed = 0;
   
           if (pmd_none(*pmd))
                   return 0;
           if (pmd_bad(*pmd)) {
                   pmd_ERROR(*pmd);
                   pmd_clear(pmd);
                   return 0;
           }
           ptep = pte_offset(pmd, address);
           offset = address & ~PMD_MASK;
           if (offset + size > PMD_SIZE)
                   size = PMD_SIZE - offset;
           size &= PAGE_MASK;
           for (offset=0; offset < size; ptep++, offset += PAGE_SIZE) {
                   pte_t pte = *ptep;
                   if (pte_none(pte))
                           continue;
                   if (pte_present(pte)) {
                           struct page *page = pte_page(pte);
                           if (VALID_PAGE(page) && !PageReserved(page))
                                   freed ++;
                           /* This will eventually call __free_pte on the pte. */
                           tlb_remove_page(tlb, ptep, address + offset);
                   } else {
                           free_swap_and_cache(pte_to_swp_entry(pte));
                           pte_clear(ptep);
                   }
           }
   
           return freed;
   }
   
   static inline int zap_pmd_range(mmu_gather_t *tlb, pgd_t * dir, unsigned long address, unsigned long size)
   {
           pmd_t * pmd;
           unsigned long end;
           int freed;
   
           if (pgd_none(*dir))
                   return 0;
           if (pgd_bad(*dir)) {
                   pgd_ERROR(*dir);
                   pgd_clear(dir);
                   return 0;
           }
           pmd = pmd_offset(dir, address);
           end = address + size;
           if (end > ((address + PGDIR_SIZE) & PGDIR_MASK))
                   end = ((address + PGDIR_SIZE) & PGDIR_MASK);
           freed = 0;
           do {
                   freed += zap_pte_range(tlb, pmd, address, end - address);
                   address = (address + PMD_SIZE) & PMD_MASK; 
                   pmd++;
           } while (address < end);
           return freed;
   }
   
   /*
    * remove user pages in a given range.
    */
   void zap_page_range(struct mm_struct *mm, unsigned long address, unsigned long size)
   {
           mmu_gather_t *tlb;
           pgd_t * dir;
           unsigned long start = address, end = address + size;
           int freed = 0;
   
           dir = pgd_offset(mm, address);
   
           /*
            * This is a long-lived spinlock. That's fine.
            * There's no contention, because the page table
            * lock only protects against kswapd anyway, and
            * even if kswapd happened to be looking at this
            * process we _want_ it to get stuck.
            */
           if (address >= end)
                   BUG();
           spin_lock(&mm->page_table_lock);
           flush_cache_range(mm, address, end);
           tlb = tlb_gather_mmu(mm);
   
           do {
                   freed += zap_pmd_range(tlb, dir, address, end - address);
                   address = (address + PGDIR_SIZE) & PGDIR_MASK;
                   dir++;
           } while (address && (address < end));
   
           /* this will flush any remaining tlb entries */
           tlb_finish_mmu(tlb, start, end);
   
           /*
            * Update rss for the mm_struct (not necessarily current->mm)
            * Notice that rss is an unsigned long.
            */
           if (mm->rss > freed)
                   mm->rss -= freed;
           else
                   mm->rss = 0;
           spin_unlock(&mm->page_table_lock);
   }
   
   /*
    * Do a quick page-table lookup for a single page. 
    */
   static struct page * follow_page(struct mm_struct *mm, unsigned long address, int write) 
   {
           pgd_t *pgd;
           pmd_t *pmd;
           pte_t *ptep, pte;
   
           pgd = pgd_offset(mm, address);
           if (pgd_none(*pgd) || pgd_bad(*pgd))
                   goto out;
   
           pmd = pmd_offset(pgd, address);
           if (pmd_none(*pmd) || pmd_bad(*pmd))
                   goto out;
   
           ptep = pte_offset(pmd, address);
           if (!ptep)
                   goto out;
   
           pte = *ptep;
           if (pte_present(pte)) {
                   if (!write ||
                       (pte_write(pte) && pte_dirty(pte)))
                           return pte_page(pte);
           }
   
   out:
           return 0;
   }
   
   /* 
    * Given a physical address, is there a useful struct page pointing to
    * it?  This may become more complex in the future if we start dealing
    * with IO-aperture pages in kiobufs.
    */
   
   static inline struct page * get_page_map(struct page *page)
   {
           if (!VALID_PAGE(page))
                   return 0;
           return page;
   }
   
   /*
    * Please read Documentation/cachetlb.txt before using this function,
    * accessing foreign memory spaces can cause cache coherency problems.
    *
    * Accessing a VM_IO area is even more dangerous, therefore the function
    * fails if pages is != NULL and a VM_IO area is found.
    */
   int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start,
                   int len, int write, int force, struct page **pages, struct vm_area_struct **vmas)
   {
           int i;
           unsigned int flags;
   
           /*
            * Require read or write permissions.
            * If 'force' is set, we only require the "MAY" flags.
            */
           flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
           flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
           i = 0;
   
           do {
                   struct vm_area_struct * vma;
   
                   vma = find_extend_vma(mm, start);
   
                   if ( !vma || (pages && vma->vm_flags & VM_IO) || !(flags & vma->vm_flags) )
                           return i ? : -EFAULT;
   
                   spin_lock(&mm->page_table_lock);
                   do {
                           struct page *map;
                           while (!(map = follow_page(mm, start, write))) {
                                   spin_unlock(&mm->page_table_lock);
                                   switch (handle_mm_fault(mm, vma, start, write)) {
                                   case 1:
                                           tsk->min_flt++;
                                           break;
                                   case 2:
                                           tsk->maj_flt++;
                                           break;
                                   case 0:
                                           if (i) return i;
                                           return -EFAULT;
                                   default:
                                           if (i) return i;
                                           return -ENOMEM;
                                   }
                                   spin_lock(&mm->page_table_lock);
                           }
                           if (pages) {
                                   pages[i] = get_page_map(map);
                                   /* FIXME: call the correct function,
                                    * depending on the type of the found page
                                    */
                                   if (!pages[i])
                                           goto bad_page;
                                   page_cache_get(pages[i]);
                           }
                           if (vmas)
                                   vmas[i] = vma;
                           i++;
                           start += PAGE_SIZE;
                           len--;
                   } while(len && start < vma->vm_end);
                   spin_unlock(&mm->page_table_lock);
           } while(len);
   out:
           return i;
   
           /*
            * We found an invalid page in the VMA.  Release all we have
            * so far and fail.
            */
   bad_page:
           spin_unlock(&mm->page_table_lock);
           while (i--)
                   page_cache_release(pages[i]);
           i = -EFAULT;
           goto out;
   }
   
   EXPORT_SYMBOL(get_user_pages);
   
   /*
    * Force in an entire range of pages from the current process's user VA,
    * and pin them in physical memory.  
    */
   #define dprintk(x...)
   
   int map_user_kiobuf(int rw, struct kiobuf *iobuf, unsigned long va, size_t len)
   {
           int pgcount, err;
           struct mm_struct *      mm;
           
           /* Make sure the iobuf is not already mapped somewhere. */
           if (iobuf->nr_pages)
                   return -EINVAL;
   
           mm = current->mm;
           dprintk ("map_user_kiobuf: begin\n");
           
           pgcount = (va + len + PAGE_SIZE - 1)/PAGE_SIZE - va/PAGE_SIZE;
           /* mapping 0 bytes is not permitted */
           if (!pgcount) BUG();
           err = expand_kiobuf(iobuf, pgcount);
           if (err)
                   return err;
   
           iobuf->locked = 0;
           iobuf->offset = va & (PAGE_SIZE-1);
           iobuf->length = len;
           
           /* Try to fault in all of the necessary pages */
           down_read(&mm->mmap_sem);
           /* rw==READ means read from disk, write into memory area */
           err = get_user_pages(current, mm, va, pgcount,
                           (rw==READ), 0, iobuf->maplist, NULL);
           up_read(&mm->mmap_sem);
           if (err < 0) {
                   unmap_kiobuf(iobuf);
                   dprintk ("map_user_kiobuf: end %d\n", err);
                   return err;
           }
           iobuf->nr_pages = err;
           while (pgcount--) {
                   /* FIXME: flush superflous for rw==READ,
                    * probably wrong function for rw==WRITE
                    */
                   flush_dcache_page(iobuf->maplist[pgcount]);
           }
           dprintk ("map_user_kiobuf: end OK\n");
           return 0;
   }
   
   /*
    * Mark all of the pages in a kiobuf as dirty 
    *
    * We need to be able to deal with short reads from disk: if an IO error
    * occurs, the number of bytes read into memory may be less than the
    * size of the kiobuf, so we have to stop marking pages dirty once the
    * requested byte count has been reached.
    *
    * Must be called from process context - set_page_dirty() takes VFS locks.
    */
   
   void mark_dirty_kiobuf(struct kiobuf *iobuf, int bytes)
   {
           int index, offset, remaining;
           struct page *page;
           
           index = iobuf->offset >> PAGE_SHIFT;
           offset = iobuf->offset & ~PAGE_MASK;
           remaining = bytes;
           if (remaining > iobuf->length)
                   remaining = iobuf->length;
           
           while (remaining > 0 && index < iobuf->nr_pages) {
                   page = iobuf->maplist[index];
                   
                   if (!PageReserved(page))
                           set_page_dirty(page);
   
                   remaining -= (PAGE_SIZE - offset);
                   offset = 0;
                   index++;
           }
   }
   
   /*
    * Unmap all of the pages referenced by a kiobuf.  We release the pages,
    * and unlock them if they were locked. 
    */
   
   void unmap_kiobuf (struct kiobuf *iobuf) 
   {
           int i;
           struct page *map;
           
           for (i = 0; i < iobuf->nr_pages; i++) {
                   map = iobuf->maplist[i];
                   if (map) {
                           if (iobuf->locked)
                                   UnlockPage(map);
                           /* FIXME: cache flush missing for rw==READ
                            * FIXME: call the correct reference counting function
                            */
                           page_cache_release(map);
                   }
           }
           
           iobuf->nr_pages = 0;
           iobuf->locked = 0;
   }
   
   
   /*
    * Lock down all of the pages of a kiovec for IO.
    *
    * If any page is mapped twice in the kiovec, we return the error -EINVAL.
    *
    * The optional wait parameter causes the lock call to block until all
    * pages can be locked if set.  If wait==0, the lock operation is
    * aborted if any locked pages are found and -EAGAIN is returned.
    */
   
   int lock_kiovec(int nr, struct kiobuf *iovec[], int wait)
   {
           struct kiobuf *iobuf;
           int i, j;
           struct page *page, **ppage;
           int doublepage = 0;
           int repeat = 0;
           
    repeat:
           
           for (i = 0; i < nr; i++) {
                   iobuf = iovec[i];
   
                   if (iobuf->locked)
                           continue;
   
                   ppage = iobuf->maplist;
                   for (j = 0; j < iobuf->nr_pages; ppage++, j++) {
                           page = *ppage;
                           if (!page)
                                   continue;
                           
                           if (TryLockPage(page)) {
                                   while (j--) {
                                           struct page *tmp = *--ppage;
                                           if (tmp)
                                                   UnlockPage(tmp);
                                   }
                                   goto retry;
                           }
                   }
                   iobuf->locked = 1;
           }
   
           return 0;
           
    retry:
           
           /* 
            * We couldn't lock one of the pages.  Undo the locking so far,
            * wait on the page we got to, and try again.  
            */
           
           unlock_kiovec(nr, iovec);
           if (!wait)
                   return -EAGAIN;
           
           /* 
            * Did the release also unlock the page we got stuck on?
            */
           if (!PageLocked(page)) {
                   /* 
                    * If so, we may well have the page mapped twice
                    * in the IO address range.  Bad news.  Of
                    * course, it _might_ just be a coincidence,
                    * but if it happens more than once, chances
                    * are we have a double-mapped page. 
                    */
                   if (++doublepage >= 3) 
                           return -EINVAL;
                   
                   /* Try again...  */
                   wait_on_page(page);
           }
           
           if (++repeat < 16)
                   goto repeat;
           return -EAGAIN;
   }
   
   /*
    * Unlock all of the pages of a kiovec after IO.
    */
   
   int unlock_kiovec(int nr, struct kiobuf *iovec[])
   {
           struct kiobuf *iobuf;
           int i, j;
           struct page *page, **ppage;
           
           for (i = 0; i < nr; i++) {
                   iobuf = iovec[i];
   
                   if (!iobuf->locked)
                           continue;
                   iobuf->locked = 0;
                   
                   ppage = iobuf->maplist;
                   for (j = 0; j < iobuf->nr_pages; ppage++, j++) {
                           page = *ppage;
                           if (!page)
                                   continue;
                           UnlockPage(page);
                   }
           }
           return 0;
   }
   
   static inline void zeromap_pte_range(pte_t * pte, unsigned long address,
                                        unsigned long size, pgprot_t prot)
   {
           unsigned long end;
   
           address &= ~PMD_MASK;
           end = address + size;
           if (end > PMD_SIZE)
                   end = PMD_SIZE;
           do {
                   pte_t zero_pte = pte_wrprotect(mk_pte(ZERO_PAGE(address), prot));
                   pte_t oldpage = ptep_get_and_clear(pte);
                   set_pte(pte, zero_pte);
                   forget_pte(oldpage);
                   address += PAGE_SIZE;
                   pte++;
           } while (address && (address < end));
   }
   
   static inline int zeromap_pmd_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address,
                                       unsigned long size, pgprot_t prot)
   {
           unsigned long end;
   
           address &= ~PGDIR_MASK;
           end = address + size;
           if (end > PGDIR_SIZE)
                   end = PGDIR_SIZE;
           do {
                   pte_t * pte = pte_alloc(mm, pmd, address);
                   if (!pte)
                           return -ENOMEM;
                   zeromap_pte_range(pte, address, end - address, prot);
                   address = (address + PMD_SIZE) & PMD_MASK;
                   pmd++;
           } while (address && (address < end));
           return 0;
   }
   
   int zeromap_page_range(unsigned long address, unsigned long size, pgprot_t prot)
   {
           int error = 0;
           pgd_t * dir;
           unsigned long beg = address;
           unsigned long end = address + size;
           struct mm_struct *mm = current->mm;
   
           dir = pgd_offset(mm, address);
           flush_cache_range(mm, beg, end);
           if (address >= end)
                   BUG();
   
           spin_lock(&mm->page_table_lock);
           do {
                   pmd_t *pmd = pmd_alloc(mm, dir, address);
                   error = -ENOMEM;
                   if (!pmd)
                           break;
                   error = zeromap_pmd_range(mm, pmd, address, end - address, prot);
                   if (error)
                           break;
                   address = (address + PGDIR_SIZE) & PGDIR_MASK;
                   dir++;
           } while (address && (address < end));
           spin_unlock(&mm->page_table_lock);
           flush_tlb_range(mm, beg, end);
           return error;
   }
   
   /*
    * maps a range of physical memory into the requested pages. the old
    * mappings are removed. any references to nonexistent pages results
    * in null mappings (currently treated as "copy-on-access")
    */
   static inline void remap_pte_range(pte_t * pte, unsigned long address, unsigned long size,
           unsigned long phys_addr, pgprot_t prot)
   {
           unsigned long end;
   
           address &= ~PMD_MASK;
           end = address + size;
           if (end > PMD_SIZE)
                   end = PMD_SIZE;
           do {
                   struct page *page;
                   pte_t oldpage;
                   oldpage = ptep_get_and_clear(pte);
   
                   page = virt_to_page(__va(phys_addr));
                   if ((!VALID_PAGE(page)) || PageReserved(page))
                           set_pte(pte, mk_pte_phys(phys_addr, prot));
                   forget_pte(oldpage);
                   address += PAGE_SIZE;
                   phys_addr += PAGE_SIZE;
                   pte++;
           } while (address && (address < end));
   }
   
   static inline int remap_pmd_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address, unsigned long size,
           unsigned long phys_addr, pgprot_t prot)
   {
           unsigned long end;
   
           address &= ~PGDIR_MASK;
           end = address + size;
           if (end > PGDIR_SIZE)
                   end = PGDIR_SIZE;
           phys_addr -= address;
           do {
                   pte_t * pte = pte_alloc(mm, pmd, address);
                   if (!pte)
                           return -ENOMEM;
                   remap_pte_range(pte, address, end - address, address + phys_addr, prot);
                   address = (address + PMD_SIZE) & PMD_MASK;
                   pmd++;
           } while (address && (address < end));
           return 0;
   }
   
   /*  Note: this is only safe if the mm semaphore is held when called. */
   int remap_page_range(unsigned long from, unsigned long phys_addr, unsigned long size, pgprot_t prot)
   {
           int error = 0;
           pgd_t * dir;
           unsigned long beg = from;
           unsigned long end = from + size;
           struct mm_struct *mm = current->mm;
   
           phys_addr -= from;
           dir = pgd_offset(mm, from);
           flush_cache_range(mm, beg, end);
           if (from >= end)
                   BUG();
   
           spin_lock(&mm->page_table_lock);
           do {
                   pmd_t *pmd = pmd_alloc(mm, dir, from);
                   error = -ENOMEM;
                   if (!pmd)
                           break;
                   error = remap_pmd_range(mm, pmd, from, end - from, phys_addr + from, prot);
                   if (error)
                           break;
                   from = (from + PGDIR_SIZE) & PGDIR_MASK;
                   dir++;
           } while (from && (from < end));
           spin_unlock(&mm->page_table_lock);
           flush_tlb_range(mm, beg, end);
           return error;
   }
   
   /*
    * Establish a new mapping:
    *  - flush the old one
    *  - update the page tables
    *  - inform the TLB about the new one
    *
    * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
    */
   static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
   {
           set_pte(page_table, entry);
           flush_tlb_page(vma, address);
           update_mmu_cache(vma, address, entry);
   }
   
   /*
    * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
    */
   static inline void break_cow(struct vm_area_struct * vma, struct page * new_page, unsigned long address, 
                   pte_t *page_table)
   {
           flush_page_to_ram(new_page);
           flush_cache_page(vma, address);
           establish_pte(vma, address, page_table, pte_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot))));
   }
   
   /*
    * This routine handles present pages, when users try to write
    * to a shared page. It is done by copying the page to a new address
    * and decrementing the shared-page counter for the old page.
    *
    * Goto-purists beware: the only reason for goto's here is that it results
    * in better assembly code.. The "default" path will see no jumps at all.
    *
    * Note that this routine assumes that the protection checks have been
    * done by the caller (the low-level page fault routine in most cases).
    * Thus we can safely just mark it writable once we've done any necessary
    * COW.
    *
    * We also mark the page dirty at this point even though the page will
    * change only once the write actually happens. This avoids a few races,
    * and potentially makes it more efficient.
    *
    * We hold the mm semaphore and the page_table_lock on entry and exit
    * with the page_table_lock released.
    */
   static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
           unsigned long address, pte_t *page_table, pte_t pte)
   {
           struct page *old_page, *new_page;
   
           old_page = pte_page(pte);
           if (!VALID_PAGE(old_page))
                   goto bad_wp_page;
   
           if (!TryLockPage(old_page)) {
                   int reuse = can_share_swap_page(old_page);
                   unlock_page(old_page);
                   if (reuse) {
                           flush_cache_page(vma, address);
                           establish_pte(vma, address, page_table, pte_mkyoung(pte_mkdirty(pte_mkwrite(pte))));
                           spin_unlock(&mm->page_table_lock);
                           return 1;       /* Minor fault */
                   }
           }
   
           /*
            * Ok, we need to copy. Oh, well..
            */
           page_cache_get(old_page);
           spin_unlock(&mm->page_table_lock);
   
           new_page = alloc_page(GFP_HIGHUSER);
           if (!new_page)
                   goto no_mem;
           copy_cow_page(old_page,new_page,address);
   
           /*
            * Re-check the pte - we dropped the lock
            */
           spin_lock(&mm->page_table_lock);
           if (pte_same(*page_table, pte)) {
                   if (PageReserved(old_page))
                           ++mm->rss;
                   break_cow(vma, new_page, address, page_table);
                   lru_cache_add(new_page);
   
                   /* Free the old page.. */
                   new_page = old_page;
           }
           spin_unlock(&mm->page_table_lock);
           page_cache_release(new_page);
           page_cache_release(old_page);
           return 1;       /* Minor fault */
   
   bad_wp_page:
           spin_unlock(&mm->page_table_lock);
           printk("do_wp_page: bogus page at address %08lx (page 0x%lx)\n",address,(unsigned long)old_page);
          return -1;
  no_mem:
          page_cache_release(old_page);
          return -1;
  }
  
  static void vmtruncate_list(struct vm_area_struct *mpnt, unsigned long pgoff)
  {
          do {
                  struct mm_struct *mm = mpnt->vm_mm;
                  unsigned long start = mpnt->vm_start;
                  unsigned long end = mpnt->vm_end;
                  unsigned long len = end - start;
                  unsigned long diff;
  
                  /* mapping wholly truncated? */
                  if (mpnt->vm_pgoff >= pgoff) {
                          zap_page_range(mm, start, len);
                          continue;
                  }
  
                  /* mapping wholly unaffected? */
                  len = len >> PAGE_SHIFT;
                  diff = pgoff - mpnt->vm_pgoff;
                  if (diff >= len)
                          continue;
  
                  /* Ok, partially affected.. */
                  start += diff << PAGE_SHIFT;
                  len = (len - diff) << PAGE_SHIFT;
                  zap_page_range(mm, start, len);
          } while ((mpnt = mpnt->vm_next_share) != NULL);
  }
  
  /*
   * Handle all mappings that got truncated by a "truncate()"
   * system call.
   *
   * NOTE! We have to be ready to update the memory sharing
   * between the file and the memory map for a potential last
   * incomplete page.  Ugly, but necessary.
   */
  int vmtruncate(struct inode * inode, loff_t offset)
  {
          unsigned long pgoff;
          struct address_space *mapping = inode->i_mapping;
          unsigned long limit;
  
          if (inode->i_size < offset)
                  goto do_expand;
          inode->i_size = offset;
          spin_lock(&mapping->i_shared_lock);
          if (!mapping->i_mmap && !mapping->i_mmap_shared)
                  goto out_unlock;
  
          pgoff = (offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
          if (mapping->i_mmap != NULL)
                  vmtruncate_list(mapping->i_mmap, pgoff);
          if (mapping->i_mmap_shared != NULL)
                  vmtruncate_list(mapping->i_mmap_shared, pgoff);
  
  out_unlock:
          spin_unlock(&mapping->i_shared_lock);
          truncate_inode_pages(mapping, offset);
          goto out_truncate;
  
  do_expand:
          limit = current->rlim[RLIMIT_FSIZE].rlim_cur;
          if (limit != RLIM_INFINITY && offset > limit)
                  goto out_sig;
          if (offset > inode->i_sb->s_maxbytes)
                  goto out;
          inode->i_size = offset;
  
  out_truncate:
          if (inode->i_op && inode->i_op->truncate) {
                  lock_kernel();
                  inode->i_op->truncate(inode);
                  unlock_kernel();
          }
          return 0;
  out_sig:
          send_sig(SIGXFSZ, current, 0);
  out:
          return -EFBIG;
  }
  
  /* 
   * Primitive swap readahead code. We simply read an aligned block of
   * (1 << page_cluster) entries in the swap area. This method is chosen
   * because it doesn't cost us any seek time.  We also make sure to queue
   * the 'original' request together with the readahead ones...  
   */
  void swapin_readahead(swp_entry_t entry)
  {
          int i, num;
          struct page *new_page;
          unsigned long offset;
  
          /*
           * Get the number of handles we should do readahead io to.
           */
          num = valid_swaphandles(entry, &offset);
          for (i = 0; i < num; offset++, i++) {
                  /* Ok, do the async read-ahead now */
                  new_page = read_swap_cache_async(SWP_ENTRY(SWP_TYPE(entry), offset));
                  if (!new_page)
                          break;
                  page_cache_release(new_page);
          }
          return;
  }
  
  /*
   * We hold the mm semaphore and the page_table_lock on entry and
   * should release the pagetable lock on exit..
   */
  static int do_swap_page(struct mm_struct * mm,
          struct vm_area_struct * vma, unsigned long address,
          pte_t * page_table, pte_t orig_pte, int write_access)
  {
          struct page *page;
          swp_entry_t entry = pte_to_swp_entry(orig_pte);
          pte_t pte;
          int ret = 1;
  
          spin_unlock(&mm->page_table_lock);
          page = lookup_swap_cache(entry);
          if (!page) {
                  swapin_readahead(entry);
                  page = read_swap_cache_async(entry);
                  if (!page) {
                          /*
                           * Back out if somebody else faulted in this pte while
                           * we released the page table lock.
                           */
                          int retval;
                          spin_lock(&mm->page_table_lock);
                          retval = pte_same(*page_table, orig_pte) ? -1 : 1;
                          spin_unlock(&mm->page_table_lock);
                          return retval;
                  }
  
                  /* Had to read the page from swap area: Major fault */
                  ret = 2;
          }
  
          mark_page_accessed(page);
  
          lock_page(page);
  
          /*
           * Back out if somebody else faulted in this pte while we
           * released the page table lock.
           */
          spin_lock(&mm->page_table_lock);
          if (!pte_same(*page_table, orig_pte)) {
                  spin_unlock(&mm->page_table_lock);
                  unlock_page(page);
                  page_cache_release(page);
                  return 1;
          }
  
          /* The page isn't present yet, go ahead with the fault. */
                  
          swap_free(entry);
          if (vm_swap_full())
                  remove_exclusive_swap_page(page);
  
          mm->rss++;
          pte = mk_pte(page, vma->vm_page_prot);
          if (write_access && can_share_swap_page(page))
                  pte = pte_mkdirty(pte_mkwrite(pte));
          unlock_page(page);
  
          flush_page_to_ram(page);
          flush_icache_page(vma, page);
          set_pte(page_table, pte);
  
          /* No need to invalidate - it was non-present before */
          update_mmu_cache(vma, address, pte);
          spin_unlock(&mm->page_table_lock);
          return ret;
  }
  
  /*
   * We are called with the MM semaphore and page_table_lock
   * spinlock held to protect against concurrent faults in
   * multithreaded programs. 
   */
  static int do_anonymous_page(struct mm_struct * mm, struct vm_area_struct * vma, pte_t *page_table, int write_access, unsigned long addr)
  {
          pte_t entry;
  
          /* Read-only mapping of ZERO_PAGE. */
          entry = pte_wrprotect(mk_pte(ZERO_PAGE(addr), vma->vm_page_prot));
  
          /* ..except if it's a write access */
          if (write_access) {
                  struct page *page;
  
                  /* Allocate our own private page. */
                  spin_unlock(&mm->page_table_lock);
  
                  page = alloc_page(GFP_HIGHUSER);
                  if (!page)
                          goto no_mem;
                  clear_user_highpage(page, addr);
  
                  spin_lock(&mm->page_table_lock);
                  if (!pte_none(*page_table)) {
                          page_cache_release(page);
                          spin_unlock(&mm->page_table_lock);
                          return 1;
                  }
                  mm->rss++;
                  flush_page_to_ram(page);
                  entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
                  lru_cache_add(page);
                  mark_page_accessed(page);
          }
  
          set_pte(page_table, entry);
  
          /* No need to invalidate - it was non-present before */
          update_mmu_cache(vma, addr, entry);
          spin_unlock(&mm->page_table_lock);
          return 1;       /* Minor fault */
  
  no_mem:
          return -1;
  }
  
  /*
   * do_no_page() tries to create a new page mapping. It aggressively
   * tries to share with existing pages, but makes a separate copy if
   * the "write_access" parameter is true in order to avoid the next
   * page fault.
   *
   * As this is called only for pages that do not currently exist, we
   * do not need to flush old virtual caches or the TLB.
   *
   * This is called with the MM semaphore held and the page table
   * spinlock held. Exit with the spinlock released.
   */
  static int do_no_page(struct mm_struct * mm, struct vm_area_struct * vma,
          unsigned long address, int write_access, pte_t *page_table)
  {
          struct page * new_page;
          pte_t entry;
  
          if (!vma->vm_ops || !vma->vm_ops->nopage)
                  return do_anonymous_page(mm, vma, page_table, write_access, address);
          spin_unlock(&mm->page_table_lock);
  
          new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, 0);
  
          if (new_page == NULL)   /* no page was available -- SIGBUS */
                  return 0;
          if (new_page == NOPAGE_OOM)
                  return -1;
  
          /*
           * Should we do an early C-O-W break?
           */
          if (write_access && !(vma->vm_flags & VM_SHARED)) {
                  struct page * page = alloc_page(GFP_HIGHUSER);
                  if (!page) {
                          page_cache_release(new_page);
                          return -1;
                  }
                  copy_user_highpage(page, new_page, address);
                  page_cache_release(new_page);
                  lru_cache_add(page);
                  new_page = page;
          }
  
          spin_lock(&mm->page_table_lock);
          /*
           * This silly early PAGE_DIRTY setting removes a race
           * due to the bad i386 page protection. But it's valid
           * for other architectures too.
           *
           * Note that if write_access is true, we either now have
           * an exclusive copy of the page, or this is a shared mapping,
           * so we can make it writable and dirty to avoid having to
           * handle that later.
           */
          /* Only go through if we didn't race with anybody else... */
          if (pte_none(*page_table)) {
                  ++mm->rss;
                  flush_page_to_ram(new_page);
                  flush_icache_page(vma, new_page);
                  entry = mk_pte(new_page, vma->vm_page_prot);
                  if (write_access)
                          entry = pte_mkwrite(pte_mkdirty(entry));
                  set_pte(page_table, entry);
          } else {
                  /* One of our sibling threads was faster, back out. */
                  page_cache_release(new_page);
                  spin_unlock(&mm->page_table_lock);
                  return 1;
          }
  
          /* no need to invalidate: a not-present page shouldn't be cached */
          update_mmu_cache(vma, address, entry);
          spin_unlock(&mm->page_table_lock);
          return 2;       /* Major fault */
  }
  
  /*
   * These routines also need to handle stuff like marking pages dirty
   * and/or accessed for architectures that don't do it in hardware (most
   * RISC architectures).  The early dirtying is also good on the i386.
   *
   * There is also a hook called "update_mmu_cache()" that architectures
   * with external mmu caches can use to update those (ie the Sparc or
   * PowerPC hashed page tables that act as extended TLBs).
   *
   * Note the "page_table_lock". It is to protect against kswapd removing
   * pages from under us. Note that kswapd only ever _removes_ pages, never
   * adds them. As such, once we have noticed that the page is not present,
   * we can drop the lock early.
   *
   * The adding of pages is protected by the MM semaphore (which we hold),
   * so we don't need to worry about a page being suddenly been added into
   * our VM.
   *
   * We enter with the pagetable spinlock held, we are supposed to
   * release it when done.
   */
  static inline int handle_pte_fault(struct mm_struct *mm,
          struct vm_area_struct * vma, unsigned long address,
          int write_access, pte_t * pte)
  {
          pte_t entry;
  
          entry = *pte;
          if (!pte_present(entry)) {
                  /*
                   * If it truly wasn't present, we know that kswapd
                   * and the PTE updates will not touch it later. So
                   * drop the lock.
                   */
                  if (pte_none(entry))
                          return do_no_page(mm, vma, address, write_access, pte);
                  return do_swap_page(mm, vma, address, pte, entry, write_access);
          }
  
          if (write_access) {
                  if (!pte_write(entry))
                          return do_wp_page(mm, vma, address, pte, entry);
  
                  entry = pte_mkdirty(entry);
          }
          entry = pte_mkyoung(entry);
          establish_pte(vma, address, pte, entry);
          spin_unlock(&mm->page_table_lock);
          return 1;
  }
  
  /*
   * By the time we get here, we already hold the mm semaphore
   */
  int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
          unsigned long address, int write_access)
  {
          pgd_t *pgd;
          pmd_t *pmd;
  
          current->state = TASK_RUNNING;
          pgd = pgd_offset(mm, address);
  
          /*
           * We need the page table lock to synchronize with kswapd
           * and the SMP-safe atomic PTE updates.
           */
          spin_lock(&mm->page_table_lock);
          pmd = pmd_alloc(mm, pgd, address);
  
          if (pmd) {
                  pte_t * pte = pte_alloc(mm, pmd, address);
                  if (pte)
                          return handle_pte_fault(mm, vma, address, write_access, pte);
          }
          spin_unlock(&mm->page_table_lock);
          return -1;
  }
  
  /*
   * Allocate page middle directory.
   *
   * We've already handled the fast-path in-line, and we own the
   * page table lock.
   *
   * On a two-level page table, this ends up actually being entirely
   * optimized away.
   */
  pmd_t *__pmd_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
  {
          pmd_t *new;
  
          /* "fast" allocation can happen without dropping the lock.. */
          new = pmd_alloc_one_fast(mm, address);
          if (!new) {
                  spin_unlock(&mm->page_table_lock);
                  new = pmd_alloc_one(mm, address);
                  spin_lock(&mm->page_table_lock);
                  if (!new)
                          return NULL;
  
                  /*
                   * Because we dropped the lock, we should re-check the
                   * entry, as somebody else could have populated it..
                   */
                  if (!pgd_none(*pgd)) {
                          pmd_free(new);
                          goto out;
                  }
          }
          pgd_populate(mm, pgd, new);
  out:
          return pmd_offset(pgd, address);
  }
  
  /*
   * Allocate the page table directory.
   *
   * We've already handled the fast-path in-line, and we own the
   * page table lock.
   */
  pte_t *pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
  {
          if (pmd_none(*pmd)) {
                  pte_t *new;
  
                  /* "fast" allocation can happen without dropping the lock.. */
                  new = pte_alloc_one_fast(mm, address);
                  if (!new) {
                          spin_unlock(&mm->page_table_lock);
                          new = pte_alloc_one(mm, address);
                          spin_lock(&mm->page_table_lock);
                          if (!new)
                                  return NULL;
  
                          /*
                           * Because we dropped the lock, we should re-check the
                           * entry, as somebody else could have populated it..
                           */
                          if (!pmd_none(*pmd)) {
                                  pte_free(new);
                                  goto out;
                          }
                  }
                  pmd_populate(mm, pmd, new);
          }
  out:
          return pte_offset(pmd, address);
  }
  
  int make_pages_present(unsigned long addr, unsigned long end)
  {
          int ret, len, write;
          struct vm_area_struct * vma;
  
          vma = find_vma(current->mm, addr);
          write = (vma->vm_flags & VM_WRITE) != 0;
          if (addr >= end)
                  BUG();
          if (end > vma->vm_end)
                  BUG();
          len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
          ret = get_user_pages(current, current->mm, addr,
                          len, write, 0, NULL, NULL);
          return ret == len ? 0 : -1;
  }
  
  struct page * vmalloc_to_page(void * vmalloc_addr)
  {
          unsigned long addr = (unsigned long) vmalloc_addr;
          struct page *page = NULL;
          pmd_t *pmd;
          pte_t *pte;
          pgd_t *pgd;
          
          pgd = pgd_offset_k(addr);
          if (!pgd_none(*pgd)) {
                  pmd = pmd_offset(pgd, addr);
                  if (!pmd_none(*pmd)) {
                          pte = pte_offset(pmd, addr);
                          if (pte_present(*pte)) {
                                  page = pte_page(*pte);
                          }
                  }
          }
          return page;
  }

Cache object: 41139b24b4cf73eef3e1c8b0f99ff229