path: root/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 <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>


unsigned long max_mapnr = 0;
unsigned long num_physpages = 0;
void * high_memory = NULL;
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_highpage(to);
		return;
	}
	copy_highpage(to, from);
}

mem_map_t * mem_map = NULL;

/*
 * 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++)
		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;

	page_dir += first;
	do {
		free_one_pgd(page_dir);
		page_dir++;
	} while (--nr);

	/* 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
 */
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;
		}
		if (pgd_none(*dst_pgd)) {
			if (!pmd_alloc(dst_pgd, 0))
				goto nomem;
		}
		
		src_pmd = pmd_offset(src_pgd, address);
		dst_pmd = pmd_offset(dst_pgd, address);

		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;
			}
			if (pmd_none(*dst_pmd)) {
				if (!pte_alloc(dst_pmd, 0))
					goto nomem;
			}
			
			src_pte = pte_offset(src_pmd, address);
			dst_pte = pte_offset(dst_pmd, address);
			
			do {
				pte_t pte = *src_pte;
				unsigned long page_nr;
				
				/* copy_one_pte */

				if (pte_none(pte))
					goto cont_copy_pte_range;
				if (!pte_present(pte)) {
					swap_duplicate(pte_to_swp_entry(pte));
					set_pte(dst_pte, pte);
					goto cont_copy_pte_range;
				}
				page_nr = pte_pagenr(pte);
				if (page_nr >= max_mapnr || 
				    PageReserved(mem_map+page_nr)) {
					set_pte(dst_pte, pte);
					goto cont_copy_pte_range;
				}
				/* If it's a COW mapping, write protect it both in the parent and the child */
				if (cow) {
					pte = pte_wrprotect(pte);
					set_pte(src_pte, pte);
				}
				/* If it's a shared mapping, mark it clean in the child */
				if (vma->vm_flags & VM_SHARED)
					pte = pte_mkclean(pte);
				set_pte(dst_pte, pte_mkold(pte));
				get_page(mem_map + page_nr);
			
cont_copy_pte_range:		address += PAGE_SIZE;
				if (address >= end)
					goto out;
				src_pte++;
				dst_pte++;
			} while ((unsigned long)src_pte & PTE_TABLE_MASK);
		
cont_copy_pmd_range:	src_pmd++;
			dst_pmd++;
		} while ((unsigned long)src_pmd & PMD_TABLE_MASK);
	}
out:
	return 0;

nomem:
	return -ENOMEM;
}

/*
 * Return indicates whether a page was freed so caller can adjust rss
 */
static inline int free_pte(pte_t page)
{
	if (pte_present(page)) {
		unsigned long nr = pte_pagenr(page);
		if (nr >= max_mapnr || PageReserved(mem_map+nr))
			return 0;
		/* 
		 * free_page() used to be able to clear swap cache
		 * entries.  We may now have to do it manually.  
		 */
		free_page_and_swap_cache(mem_map+nr);
		return 1;
	}
	swap_free(pte_to_swp_entry(page));
	return 0;
}

static inline void forget_pte(pte_t page)
{
	if (!pte_none(page)) {
		printk("forget_pte: old mapping existed!\n");
		free_pte(page);
	}
}

static inline int zap_pte_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address, unsigned long size)
{
	pte_t * pte;
	int freed;

	if (pmd_none(*pmd))
		return 0;
	if (pmd_bad(*pmd)) {
		pmd_ERROR(*pmd);
		pmd_clear(pmd);
		return 0;
	}
	pte = pte_offset(pmd, address);
	address &= ~PMD_MASK;
	if (address + size > PMD_SIZE)
		size = PMD_SIZE - address;
	size >>= PAGE_SHIFT;
	freed = 0;
	for (;;) {
		pte_t page;
		if (!size)
			break;
		page = *pte;
		pte++;
		size--;
		pte_clear(pte-1);
		if (pte_none(page))
			continue;
		freed += free_pte(page);
	}
	return freed;
}

static inline int zap_pmd_range(struct mm_struct *mm, 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);
	address &= ~PGDIR_MASK;
	end = address + size;
	if (end > PGDIR_SIZE)
		end = PGDIR_SIZE;
	freed = 0;
	do {
		freed += zap_pte_range(mm, 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)
{
	pgd_t * dir;
	unsigned long 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);
	do {
		freed += zap_pmd_range(mm, dir, address, end - address);
		address = (address + PGDIR_SIZE) & PGDIR_MASK;
		dir++;
	} while (address && (address < end));
	spin_unlock(&mm->page_table_lock);
	/*
	 * Update rss for the mm_struct (not necessarily current->mm)
	 */
	if (mm->rss > 0) {
		mm->rss -= freed;
		if (mm->rss < 0)
			mm->rss = 0;
	}
}


/*
 * Do a quick page-table lookup for a single page. 
 */
static struct page * follow_page(unsigned long address) 
{
	pgd_t *pgd;
	pmd_t *pmd;

	pgd = pgd_offset(current->mm, address);
	pmd = pmd_offset(pgd, address);
	if (pmd) {
		pte_t * pte = pte_offset(pmd, address);
		if (pte && pte_present(*pte))
			return pte_page(*pte);
	}
	
	printk(KERN_ERR "Missing page in follow_page\n");
	return NULL;
}

/* 
 * Given a physical address, is there a useful struct page pointing to it?
 */

struct page * get_page_map(struct page *page, unsigned long vaddr)
{
	if (MAP_NR(vaddr) >= max_mapnr)
		return 0;
	if (page == ZERO_PAGE(vaddr))
		return 0;
	if (PageReserved(page))
		return 0;
	return page;
}

/*
 * Force in an entire range of pages from the current process's user VA,
 * and pin and lock the pages for IO.  
 */

#define dprintk(x...)
int map_user_kiobuf(int rw, struct kiobuf *iobuf, unsigned long va, size_t len)
{
	unsigned long		ptr, end;
	int			err;
	struct mm_struct *	mm;
	struct vm_area_struct *	vma = 0;
	struct page *		map;
	int			doublepage = 0;
	int			repeat = 0;
	int			i;
	
	/* Make sure the iobuf is not already mapped somewhere. */
	if (iobuf->nr_pages)
		return -EINVAL;

	mm = current->mm;
	dprintk ("map_user_kiobuf: begin\n");
	
	ptr = va & PAGE_MASK;
	end = (va + len + PAGE_SIZE - 1) & PAGE_MASK;
	err = expand_kiobuf(iobuf, (end - ptr) >> PAGE_SHIFT);
	if (err)
		return err;

 repeat:
	down(&mm->mmap_sem);

	err = -EFAULT;
	iobuf->locked = 1;
	iobuf->offset = va & ~PAGE_MASK;
	iobuf->length = len;
	
	i = 0;
	
	/* 
	 * First of all, try to fault in all of the necessary pages
	 */
	while (ptr < end) {
		if (!vma || ptr >= vma->vm_end) {
			vma = find_vma(current->mm, ptr);
			if (!vma) 
				goto out_unlock;
		}
		if (handle_mm_fault(current, vma, ptr, (rw==READ)) <= 0) 
			goto out_unlock;
		spin_lock(&mm->page_table_lock);
		map = follow_page(ptr);
		if (!map) {
			dprintk (KERN_ERR "Missing page in map_user_kiobuf\n");
			goto retry;
		}
		map = get_page_map(map, ptr);
		if (map) {
			if (TryLockPage(map)) {
				goto retry;
			}
			atomic_inc(&map->count);
		}
		spin_unlock(&mm->page_table_lock);
		iobuf->maplist[i] = map;
		iobuf->nr_pages = ++i;
		
		ptr += PAGE_SIZE;
	}

	up(&mm->mmap_sem);
	dprintk ("map_user_kiobuf: end OK\n");
	return 0;

 out_unlock:
	up(&mm->mmap_sem);
	unmap_kiobuf(iobuf);
	dprintk ("map_user_kiobuf: end %d\n", err);
	return err;

 retry:

	/* 
	 * Undo the locking so far, wait on the page we got to, and try again.
	 */
	spin_unlock(&mm->page_table_lock);
	unmap_kiobuf(iobuf);
	up(&mm->mmap_sem);

	/* 
	 * Did the release also unlock the page we got stuck on?
	 */
	if (map) {
		if (!PageLocked(map)) {
			/* 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(map);
	}
	
	if (++repeat < 16) {
		ptr = va & PAGE_MASK;
		goto repeat;
	}
	return -EAGAIN;
}


/*
 * 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 && iobuf->locked) {
			UnlockPage(map);
			__free_page(map);
		}
	}
	
	iobuf->nr_pages = 0;
	iobuf->locked = 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 = *pte;
		set_pte(pte, zero_pte);
		forget_pte(oldpage);
		address += PAGE_SIZE;
		pte++;
	} while (address && (address < end));
}

static inline int zeromap_pmd_range(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(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;

	dir = pgd_offset(current->mm, address);
	flush_cache_range(current->mm, beg, end);
	if (address >= end)
		BUG();
	do {
		pmd_t *pmd = pmd_alloc(dir, address);
		error = -ENOMEM;
		if (!pmd)
			break;
		error = zeromap_pmd_range(pmd, address, end - address, prot);
		if (error)
			break;
		address = (address + PGDIR_SIZE) & PGDIR_MASK;
		dir++;
	} while (address && (address < end));
	flush_tlb_range(current->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 {
		unsigned long mapnr;
		pte_t oldpage = *pte;
		pte_clear(pte);

		mapnr = MAP_NR(__va(phys_addr));
		if (mapnr >= max_mapnr || PageReserved(mem_map+mapnr))
 			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(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(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;
}

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;

	phys_addr -= from;
	dir = pgd_offset(current->mm, from);
	flush_cache_range(current->mm, beg, end);
	if (from >= end)
		BUG();
	do {
		pmd_t *pmd = pmd_alloc(dir, from);
		error = -ENOMEM;
		if (!pmd)
			break;
		error = remap_pmd_range(pmd, from, end - from, phys_addr + from, prot);
		if (error)
			break;
		from = (from + PGDIR_SIZE) & PGDIR_MASK;
		dir++;
	} while (from && (from < end));
	flush_tlb_range(current->mm, beg, end);
	return error;
}

/*
 * Establish a new mapping:
 *  - flush the old one
 *  - update the page tables
 *  - inform the TLB about the new one
 */
static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
{
	flush_tlb_page(vma, address);
	set_pte(page_table, entry);
	update_mmu_cache(vma, address, entry);
}

/*
 * 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 enter with the page table read-lock held, and need to exit without
 * it.
 */
static int do_wp_page(struct task_struct * tsk, struct vm_area_struct * vma,
	unsigned long address, pte_t *page_table, pte_t pte)
{
	unsigned long map_nr;
	struct page *old_page, *new_page;

	map_nr = pte_pagenr(pte);
	if (map_nr >= max_mapnr)
		goto bad_wp_page;
	tsk->min_flt++;
	old_page = mem_map + map_nr;
	
	/*
	 * We can avoid the copy if:
	 * - we're the only user (count == 1)
	 * - the only other user is the swap cache,
	 *   and the only swap cache user is itself,
	 *   in which case we can remove the page
	 *   from the swap cache.
	 */
	switch (page_count(old_page)) {
	case 2:
		/*
		 * Lock the page so that no one can look it up from
		 * the swap cache, grab a reference and start using it.
		 * Can not do lock_page, holding page_table_lock.
		 */
		if (!PageSwapCache(old_page) || TryLockPage(old_page))
			break;
		if (is_page_shared(old_page)) {
			UnlockPage(old_page);
			break;
		}
		delete_from_swap_cache_nolock(old_page);
		UnlockPage(old_page);
		/* FallThrough */
	case 1:
		flush_cache_page(vma, address);
		establish_pte(vma, address, page_table, pte_mkyoung(pte_mkdirty(pte_mkwrite(pte))));
		spin_unlock(&tsk->mm->page_table_lock);
		return 1;
	}

	/*
	 * Ok, we need to copy. Oh, well..
	 */
	spin_unlock(&tsk->mm->page_table_lock);
	new_page = alloc_page(GFP_HIGHUSER);
	if (!new_page)
		return -1;
	spin_lock(&tsk->mm->page_table_lock);

	/*
	 * Re-check the pte - we dropped the lock
	 */
	if (pte_val(*page_table) == pte_val(pte)) {
		if (PageReserved(old_page))
			++vma->vm_mm->rss;
		copy_cow_page(old_page, new_page, address);
		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))));

		/* Free the old page.. */
		new_page = old_page;
	}
	spin_unlock(&tsk->mm->page_table_lock);
	__free_page(new_page);
	return 1;

bad_wp_page:
	spin_unlock(&tsk->mm->page_table_lock);
	printk("do_wp_page: bogus page at address %08lx (nr %ld)\n",address,map_nr);
	return -1;
}

/*
 * This function zeroes out partial mmap'ed pages at truncation time..
 */
static void partial_clear(struct vm_area_struct *vma, unsigned long address)
{
	unsigned int offset;
	struct page *page;
	pgd_t *page_dir;
	pmd_t *page_middle;
	pte_t *page_table, pte;

	page_dir = pgd_offset(vma->vm_mm, address);
	if (pgd_none(*page_dir))
		return;
	if (pgd_bad(*page_dir)) {
		pgd_ERROR(*page_dir);
		pgd_clear(page_dir);
		return;
	}
	page_middle = pmd_offset(page_dir, address);
	if (pmd_none(*page_middle))
		return;
	if (pmd_bad(*page_middle)) {
		pmd_ERROR(*page_middle);
		pmd_clear(page_middle);
		return;
	}
	page_table = pte_offset(page_middle, address);
	pte = *page_table;
	if (!pte_present(pte))
		return;
	flush_cache_page(vma, address);
	page = pte_page(pte);
	if (page-mem_map >= max_mapnr)
		return;
	offset = address & ~PAGE_MASK;
	memclear_highpage_flush(page, offset, PAGE_SIZE - offset);
}

/*
 * 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.
 */
void vmtruncate(struct inode * inode, loff_t offset)
{
	unsigned long partial, pgoff;
	struct vm_area_struct * mpnt;
	struct address_space *mapping = inode->i_mapping;

	if (inode->i_size < offset)
		goto out;
	inode->i_size = offset;
	truncate_inode_pages(mapping, offset);
	spin_lock(&mapping->i_shared_lock);
	if (!mapping->i_mmap)
		goto out_unlock;

	pgoff = (offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
	partial = (unsigned long)offset & (PAGE_CACHE_SIZE - 1);

	mpnt = mapping->i_mmap;
	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) {
			flush_cache_range(mm, start, end);
			zap_page_range(mm, start, len);
			flush_tlb_range(mm, start, end);
			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;
		if (start & ~PAGE_MASK) {
			partial_clear(mpnt, start);
			start = (start + ~PAGE_MASK) & PAGE_MASK;
		}
		flush_cache_range(mm, start, end);
		zap_page_range(mm, start, len);
		flush_tlb_range(mm, start, end);
	} while ((mpnt = mpnt->vm_next_share) != NULL);
out_unlock:
	spin_unlock(&mapping->i_shared_lock);
out:
	/* this should go into ->truncate */
	inode->i_size = offset;
	if (inode->i_op && inode->i_op->truncate)
		inode->i_op->truncate(inode);
}



/* 
 * 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. Also,
	 * grab temporary references on them, releasing them as io completes.
	 */
	num = valid_swaphandles(entry, &offset);
	for (i = 0; i < num; offset++, i++) {
		/* Don't block on I/O for read-ahead */
		if (atomic_read(&nr_async_pages) >= pager_daemon.swap_cluster) {
			while (i++ < num)
				swap_free(SWP_ENTRY(SWP_TYPE(entry), offset++));
			break;
		}
		/* Ok, do the async read-ahead now */
		new_page = read_swap_cache_async(SWP_ENTRY(SWP_TYPE(entry), offset), 0);
		if (new_page != NULL)
			__free_page(new_page);
		swap_free(SWP_ENTRY(SWP_TYPE(entry), offset));
	}
	return;
}

static int do_swap_page(struct task_struct * tsk,
	struct vm_area_struct * vma, unsigned long address,
	pte_t * page_table, swp_entry_t entry, int write_access)
{
	struct page *page = lookup_swap_cache(entry);
	pte_t pte;

	if (!page) {
		lock_kernel();
		swapin_readahead(entry);
		page = read_swap_cache(entry);
		unlock_kernel();
		if (!page)
			return -1;

		flush_page_to_ram(page);
		flush_icache_page(vma, page);
	}

	vma->vm_mm->rss++;
	tsk->min_flt++;

	pte = mk_pte(page, vma->vm_page_prot);

	set_bit(PG_swap_entry, &page->flags);

	/*
	 * Freeze the "shared"ness of the page, ie page_count + swap_count.
	 * Must lock page before transferring our swap count to already
	 * obtained page count.
	 */
	lock_page(page);
	swap_free(entry);
	if (write_access && !is_page_shared(page)) {
		delete_from_swap_cache_nolock(page);
		UnlockPage(page);
		page = replace_with_highmem(page);
		pte = mk_pte(page, vma->vm_page_prot);
		pte = pte_mkwrite(pte_mkdirty(pte));
	} else
		UnlockPage(page);

	set_pte(page_table, pte);
	/* No need to invalidate - it was non-present before */
	update_mmu_cache(vma, address, pte);
	return 1;
}

/*
 * This only needs the MM semaphore
 */
static int do_anonymous_page(struct task_struct * tsk, struct vm_area_struct * vma, pte_t *page_table, int write_access, unsigned long addr)
{
	int high = 0;
	struct page *page = NULL;
	pte_t entry = pte_wrprotect(mk_pte(ZERO_PAGE(addr), vma->vm_page_prot));
	if (write_access) {
		page = alloc_page(GFP_HIGHUSER);
		if (!page)
			return -1;
		if (PageHighMem(page))
			high = 1;
		clear_highpage(page);
		entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
		vma->vm_mm->rss++;
		tsk->min_flt++;
		flush_page_to_ram(page);
	}
	set_pte(page_table, entry);
	/* No need to invalidate - it was non-present before */
	update_mmu_cache(vma, addr, entry);
	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.
 */
static int do_no_page(struct task_struct * tsk, 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(tsk, vma, page_table, write_access, address);

	/*
	 * The third argument is "no_share", which tells the low-level code
	 * to copy, not share the page even if sharing is possible.  It's
	 * essentially an early COW detection.
	 */
	new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, (vma->vm_flags & VM_SHARED)?0:write_access);
	if (new_page == NULL)	/* no page was available -- SIGBUS */
		return 0;
	if (new_page == NOPAGE_OOM)
		return -1;
	++tsk->maj_flt;
	++vma->vm_mm->rss;
	/*
	 * 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.
	 */
	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));
	} else if (page_count(new_page) > 1 &&
		   !(vma->vm_flags & VM_SHARED))
		entry = pte_wrprotect(entry);
	set_pte(page_table, entry);
	/* no need to invalidate: a not-present page shouldn't be cached */
	update_mmu_cache(vma, address, entry);
	return 1;
}

/*
 * 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.
 */
static inline int handle_pte_fault(struct task_struct *tsk,
	struct vm_area_struct * vma, unsigned long address,
	int write_access, pte_t * pte)
{
	pte_t entry;

	entry = *pte;
	if (!pte_present(entry)) {
		if (pte_none(entry))
			return do_no_page(tsk, vma, address, write_access, pte);
		return do_swap_page(tsk, vma, address, pte, pte_to_swp_entry(entry), write_access);
	}

	/*
	 * Ok, the entry was present, we need to get the page table
	 * lock to synchronize with kswapd, and verify that the entry
	 * didn't change from under us..
	 */
	spin_lock(&tsk->mm->page_table_lock);
	if (pte_val(entry) == pte_val(*pte)) {
		if (write_access) {
			if (!pte_write(entry))
				return do_wp_page(tsk, vma, address, pte, entry);

			entry = pte_mkdirty(entry);
		}
		entry = pte_mkyoung(entry);
		establish_pte(vma, address, pte, entry);
	}
	spin_unlock(&tsk->mm->page_table_lock);
	return 1;
}

/*
 * By the time we get here, we already hold the mm semaphore
 */
int handle_mm_fault(struct task_struct *tsk, struct vm_area_struct * vma,
	unsigned long address, int write_access)
{
	int ret = -1;
	pgd_t *pgd;
	pmd_t *pmd;

	pgd = pgd_offset(vma->vm_mm, address);
	pmd = pmd_alloc(pgd, address);
	
	if (pmd) {
		pte_t * pte = pte_alloc(pmd, address);
		if (pte)
			ret = handle_pte_fault(tsk, vma, address, write_access, pte);
	}
	return ret;
}

/*
 * Simplistic page force-in..
 */
int make_pages_present(unsigned long addr, unsigned long end)
{
	int write;
	struct task_struct *tsk = current;
	struct vm_area_struct * vma;

	vma = find_vma(tsk->mm, addr);
	write = (vma->vm_flags & VM_WRITE) != 0;
	if (addr >= end)
		BUG();
	do {
		if (handle_mm_fault(tsk, vma, addr, write) < 0)
			return -1;
		addr += PAGE_SIZE;
	} while (addr < end);
	return 0;
}