text: /*
   * mm/truncate.c - code for taking down pages from address_spaces
   *
   * Copyright (C) 2002, Linus Torvalds
   *
   * 10Sep2002	Andrew Morton
   *		Initial version.
   */
  
  #include <linux/kernel.h>
  #include <linux/backing-dev.h>
  #include <linux/dax.h>
  #include <linux/gfp.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/export.h>
  #include <linux/pagemap.h>
  #include <linux/highmem.h>
  #include <linux/pagevec.h>
  #include <linux/task_io_accounting_ops.h>
  #include <linux/buffer_head.h>	/* grr. try_to_release_page,
  				   do_invalidatepage */
  #include <linux/shmem_fs.h>
  #include <linux/cleancache.h>
  #include <linux/rmap.h>
  #include "internal.h"
  
  /*
   * Regular page slots are stabilized by the page lock even without the tree
   * itself locked.  These unlocked entries need verification under the tree
   * lock.
   */
  static inline void __clear_shadow_entry(struct address_space *mapping,
  				pgoff_t index, void *entry)
  {
  	XA_STATE(xas, &mapping->i_pages, index);
  
  	xas_set_update(&xas, workingset_update_node);
  	if (xas_load(&xas) != entry)
  		return;
  	xas_store(&xas, NULL);
  	mapping->nrexceptional--;
  }
  
  static void clear_shadow_entry(struct address_space *mapping, pgoff_t index,
  			       void *entry)
  {
  	xa_lock_irq(&mapping->i_pages);
  	__clear_shadow_entry(mapping, index, entry);
  	xa_unlock_irq(&mapping->i_pages);
  }
  
  /*
   * Unconditionally remove exceptional entries. Usually called from truncate
   * path. Note that the pagevec may be altered by this function by removing
   * exceptional entries similar to what pagevec_remove_exceptionals does.
   */
  static void truncate_exceptional_pvec_entries(struct address_space *mapping,
  				struct pagevec *pvec, pgoff_t *indices,
  				pgoff_t end)
  {
  	int i, j;
  	bool dax, lock;
  
  	/* Handled by shmem itself */
  	if (shmem_mapping(mapping))
  		return;
  
  	for (j = 0; j < pagevec_count(pvec); j++)
  		if (xa_is_value(pvec->pages[j]))
  			break;
  
  	if (j == pagevec_count(pvec))
  		return;
  
  	dax = dax_mapping(mapping);
  	lock = !dax && indices[j] < end;
  	if (lock)
  		xa_lock_irq(&mapping->i_pages);
  
  	for (i = j; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];
  		pgoff_t index = indices[i];
  
  		if (!xa_is_value(page)) {
  			pvec->pages[j++] = page;
  			continue;
  		}
  
  		if (index >= end)
  			continue;
  
  		if (unlikely(dax)) {
  			dax_delete_mapping_entry(mapping, index);
  			continue;
  		}
  
  		__clear_shadow_entry(mapping, index, page);
  	}
  
  	if (lock)
  		xa_unlock_irq(&mapping->i_pages);
  	pvec->nr = j;
  }
  
  /*
   * Invalidate exceptional entry if easily possible. This handles exceptional
   * entries for invalidate_inode_pages().
   */
  static int invalidate_exceptional_entry(struct address_space *mapping,
  					pgoff_t index, void *entry)
  {
  	/* Handled by shmem itself, or for DAX we do nothing. */
  	if (shmem_mapping(mapping) || dax_mapping(mapping))
  		return 1;
  	clear_shadow_entry(mapping, index, entry);
  	return 1;
  }
  
  /*
   * Invalidate exceptional entry if clean. This handles exceptional entries for
   * invalidate_inode_pages2() so for DAX it evicts only clean entries.
   */
  static int invalidate_exceptional_entry2(struct address_space *mapping,
  					 pgoff_t index, void *entry)
  {
  	/* Handled by shmem itself */
  	if (shmem_mapping(mapping))
  		return 1;
  	if (dax_mapping(mapping))
  		return dax_invalidate_mapping_entry_sync(mapping, index);
  	clear_shadow_entry(mapping, index, entry);
  	return 1;
  }
  
  /**
   * do_invalidatepage - invalidate part or all of a page
   * @page: the page which is affected
   * @offset: start of the range to invalidate
   * @length: length of the range to invalidate
   *
   * do_invalidatepage() is called when all or part of the page has become
   * invalidated by a truncate operation.
   *
   * do_invalidatepage() does not have to release all buffers, but it must
   * ensure that no dirty buffer is left outside @offset and that no I/O
   * is underway against any of the blocks which are outside the truncation
   * point.  Because the caller is about to free (and possibly reuse) those
   * blocks on-disk.
   */
  void do_invalidatepage(struct page *page, unsigned int offset,
  		       unsigned int length)
  {
  	void (*invalidatepage)(struct page *, unsigned int, unsigned int);
  
  	invalidatepage = page->mapping->a_ops->invalidatepage;
  #ifdef CONFIG_BLOCK
  	if (!invalidatepage)
  		invalidatepage = block_invalidatepage;
  #endif
  	if (invalidatepage)
  		(*invalidatepage)(page, offset, length);
  }
  
  /*
   * If truncate cannot remove the fs-private metadata from the page, the page
   * becomes orphaned.  It will be left on the LRU and may even be mapped into
   * user pagetables if we're racing with filemap_fault().
   *
   * We need to bale out if page->mapping is no longer equal to the original
   * mapping.  This happens a) when the VM reclaimed the page while we waited on
   * its lock, b) when a concurrent invalidate_mapping_pages got there first and
   * c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
   */
  static void
  truncate_cleanup_page(struct address_space *mapping, struct page *page)
  {
  	if (page_mapped(page)) {
  		pgoff_t nr = PageTransHuge(page) ? HPAGE_PMD_NR : 1;
  		unmap_mapping_pages(mapping, page->index, nr, false);
  	}
  
  	if (page_has_private(page))
  		do_invalidatepage(page, 0, PAGE_SIZE);
  
  	/*
  	 * Some filesystems seem to re-dirty the page even after
  	 * the VM has canceled the dirty bit (eg ext3 journaling).
  	 * Hence dirty accounting check is placed after invalidation.
  	 */
  	cancel_dirty_page(page);
  	ClearPageMappedToDisk(page);
  }
  
  /*
   * This is for invalidate_mapping_pages().  That function can be called at
   * any time, and is not supposed to throw away dirty pages.  But pages can
   * be marked dirty at any time too, so use remove_mapping which safely
   * discards clean, unused pages.
   *
   * Returns non-zero if the page was successfully invalidated.
   */
  static int
  invalidate_complete_page(struct address_space *mapping, struct page *page)
  {
  	int ret;
  
  	if (page->mapping != mapping)
  		return 0;
  
  	if (page_has_private(page) && !try_to_release_page(page, 0))
  		return 0;
  
  	ret = remove_mapping(mapping, page);
  
  	return ret;
  }
  
  int truncate_inode_page(struct address_space *mapping, struct page *page)
  {
  	VM_BUG_ON_PAGE(PageTail(page), page);
  
  	if (page->mapping != mapping)
  		return -EIO;
  
  	truncate_cleanup_page(mapping, page);
  	delete_from_page_cache(page);
  	return 0;
  }
  
  /*
   * Used to get rid of pages on hardware memory corruption.
   */
  int generic_error_remove_page(struct address_space *mapping, struct page *page)
  {
  	if (!mapping)
  		return -EINVAL;
  	/*
  	 * Only punch for normal data pages for now.
  	 * Handling other types like directories would need more auditing.
  	 */
  	if (!S_ISREG(mapping->host->i_mode))
  		return -EIO;
  	return truncate_inode_page(mapping, page);
  }
  EXPORT_SYMBOL(generic_error_remove_page);
  
  /*
   * Safely invalidate one page from its pagecache mapping.
   * It only drops clean, unused pages. The page must be locked.
   *
   * Returns 1 if the page is successfully invalidated, otherwise 0.
   */
  int invalidate_inode_page(struct page *page)
  {
  	struct address_space *mapping = page_mapping(page);
  	if (!mapping)
  		return 0;
  	if (PageDirty(page) || PageWriteback(page))
  		return 0;
  	if (page_mapped(page))
  		return 0;
  	return invalidate_complete_page(mapping, page);
  }
  
  /**
   * truncate_inode_pages_range - truncate range of pages specified by start & end byte offsets
   * @mapping: mapping to truncate
   * @lstart: offset from which to truncate
   * @lend: offset to which to truncate (inclusive)
   *
   * Truncate the page cache, removing the pages that are between
   * specified offsets (and zeroing out partial pages
   * if lstart or lend + 1 is not page aligned).
   *
   * Truncate takes two passes - the first pass is nonblocking.  It will not
   * block on page locks and it will not block on writeback.  The second pass
   * will wait.  This is to prevent as much IO as possible in the affected region.
   * The first pass will remove most pages, so the search cost of the second pass
   * is low.
   *
   * We pass down the cache-hot hint to the page freeing code.  Even if the
   * mapping is large, it is probably the case that the final pages are the most
   * recently touched, and freeing happens in ascending file offset order.
   *
   * Note that since ->invalidatepage() accepts range to invalidate
   * truncate_inode_pages_range is able to handle cases where lend + 1 is not
   * page aligned properly.
   */
  void truncate_inode_pages_range(struct address_space *mapping,
  				loff_t lstart, loff_t lend)
  {
  	pgoff_t		start;		/* inclusive */
  	pgoff_t		end;		/* exclusive */
  	unsigned int	partial_start;	/* inclusive */
  	unsigned int	partial_end;	/* exclusive */
  	struct pagevec	pvec;
  	pgoff_t		indices[PAGEVEC_SIZE];
  	pgoff_t		index;
  	int		i;
  
  	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
  		goto out;
  
  	/* Offsets within partial pages */
  	partial_start = lstart & (PAGE_SIZE - 1);
  	partial_end = (lend + 1) & (PAGE_SIZE - 1);
  
  	/*
  	 * 'start' and 'end' always covers the range of pages to be fully
  	 * truncated. Partial pages are covered with 'partial_start' at the
  	 * start of the range and 'partial_end' at the end of the range.
  	 * Note that 'end' is exclusive while 'lend' is inclusive.
  	 */
  	start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if (lend == -1)
  		/*
  		 * lend == -1 indicates end-of-file so we have to set 'end'
  		 * to the highest possible pgoff_t and since the type is
  		 * unsigned we're using -1.
  		 */
  		end = -1;
  	else
  		end = (lend + 1) >> PAGE_SHIFT;
  
  	pagevec_init(&pvec);
  	index = start;
  	while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE),
  			indices)) {
  		/*
  		 * Pagevec array has exceptional entries and we may also fail
  		 * to lock some pages. So we store pages that can be deleted
  		 * in a new pagevec.
  		 */
  		struct pagevec locked_pvec;
  
  		pagevec_init(&locked_pvec);
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  
  			/* We rely upon deletion not changing page->index */
  			index = indices[i];
  			if (index >= end)
  				break;
  
  			if (xa_is_value(page))
  				continue;
  
  			if (!trylock_page(page))
  				continue;
  			WARN_ON(page_to_index(page) != index);
  			if (PageWriteback(page)) {
  				unlock_page(page);
  				continue;
  			}
  			if (page->mapping != mapping) {
  				unlock_page(page);
  				continue;
  			}
  			pagevec_add(&locked_pvec, page);
  		}
  		for (i = 0; i < pagevec_count(&locked_pvec); i++)
  			truncate_cleanup_page(mapping, locked_pvec.pages[i]);
  		delete_from_page_cache_batch(mapping, &locked_pvec);
  		for (i = 0; i < pagevec_count(&locked_pvec); i++)
  			unlock_page(locked_pvec.pages[i]);
  		truncate_exceptional_pvec_entries(mapping, &pvec, indices, end);
  		pagevec_release(&pvec);
  		cond_resched();
  		index++;
  	}
  	if (partial_start) {
  		struct page *page = find_lock_page(mapping, start - 1);
  		if (page) {
  			unsigned int top = PAGE_SIZE;
  			if (start > end) {
  				/* Truncation within a single page */
  				top = partial_end;
  				partial_end = 0;
  			}
  			wait_on_page_writeback(page);
  			zero_user_segment(page, partial_start, top);
  			cleancache_invalidate_page(mapping, page);
  			if (page_has_private(page))
  				do_invalidatepage(page, partial_start,
  						  top - partial_start);
  			unlock_page(page);
  			put_page(page);
  		}
  	}
  	if (partial_end) {
  		struct page *page = find_lock_page(mapping, end);
  		if (page) {
  			wait_on_page_writeback(page);
  			zero_user_segment(page, 0, partial_end);
  			cleancache_invalidate_page(mapping, page);
  			if (page_has_private(page))
  				do_invalidatepage(page, 0,
  						  partial_end);
  			unlock_page(page);
  			put_page(page);
  		}
  	}
  	/*
  	 * If the truncation happened within a single page no pages
  	 * will be released, just zeroed, so we can bail out now.
  	 */
  	if (start >= end)
  		goto out;
  
  	index = start;
  	for ( ; ; ) {
  		cond_resched();
  		if (!pagevec_lookup_entries(&pvec, mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) {
  			/* If all gone from start onwards, we're done */
  			if (index == start)
  				break;
  			/* Otherwise restart to make sure all gone */
  			index = start;
  			continue;
  		}
  		if (index == start && indices[0] >= end) {
  			/* All gone out of hole to be punched, we're done */
  			pagevec_remove_exceptionals(&pvec);
  			pagevec_release(&pvec);
  			break;
  		}
  
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  
  			/* We rely upon deletion not changing page->index */
  			index = indices[i];
  			if (index >= end) {
  				/* Restart punch to make sure all gone */
  				index = start - 1;
  				break;
  			}
  
  			if (xa_is_value(page))
  				continue;
  
  			lock_page(page);
  			WARN_ON(page_to_index(page) != index);
  			wait_on_page_writeback(page);
  			truncate_inode_page(mapping, page);
  			unlock_page(page);
  		}
  		truncate_exceptional_pvec_entries(mapping, &pvec, indices, end);
  		pagevec_release(&pvec);
  		index++;
  	}
  
  out:
  	cleancache_invalidate_inode(mapping);
  }
  EXPORT_SYMBOL(truncate_inode_pages_range);
  
  /**
   * truncate_inode_pages - truncate *all* the pages from an offset
   * @mapping: mapping to truncate
   * @lstart: offset from which to truncate
   *
   * Called under (and serialised by) inode->i_mutex.
   *
   * Note: When this function returns, there can be a page in the process of
   * deletion (inside __delete_from_page_cache()) in the specified range.  Thus
   * mapping->nrpages can be non-zero when this function returns even after
   * truncation of the whole mapping.
   */
  void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
  {
  	truncate_inode_pages_range(mapping, lstart, (loff_t)-1);
  }
  EXPORT_SYMBOL(truncate_inode_pages);
  
  /**
   * truncate_inode_pages_final - truncate *all* pages before inode dies
   * @mapping: mapping to truncate
   *
   * Called under (and serialized by) inode->i_mutex.
   *
   * Filesystems have to use this in the .evict_inode path to inform the
   * VM that this is the final truncate and the inode is going away.
   */
  void truncate_inode_pages_final(struct address_space *mapping)
  {
  	unsigned long nrexceptional;
  	unsigned long nrpages;
  
  	/*
  	 * Page reclaim can not participate in regular inode lifetime
  	 * management (can't call iput()) and thus can race with the
  	 * inode teardown.  Tell it when the address space is exiting,
  	 * so that it does not install eviction information after the
  	 * final truncate has begun.
  	 */
  	mapping_set_exiting(mapping);
  
  	/*
  	 * When reclaim installs eviction entries, it increases
  	 * nrexceptional first, then decreases nrpages.  Make sure we see
  	 * this in the right order or we might miss an entry.
  	 */
  	nrpages = mapping->nrpages;
  	smp_rmb();
  	nrexceptional = mapping->nrexceptional;
  
  	if (nrpages || nrexceptional) {
  		/*
  		 * As truncation uses a lockless tree lookup, cycle
  		 * the tree lock to make sure any ongoing tree
  		 * modification that does not see AS_EXITING is
  		 * completed before starting the final truncate.
  		 */
  		xa_lock_irq(&mapping->i_pages);
  		xa_unlock_irq(&mapping->i_pages);
  	}
  
  	/*
  	 * Cleancache needs notification even if there are no pages or shadow
  	 * entries.
  	 */
  	truncate_inode_pages(mapping, 0);
  }
  EXPORT_SYMBOL(truncate_inode_pages_final);
  
  /**
   * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
   * @mapping: the address_space which holds the pages to invalidate
   * @start: the offset 'from' which to invalidate
   * @end: the offset 'to' which to invalidate (inclusive)
   *
   * This function only removes the unlocked pages, if you want to
   * remove all the pages of one inode, you must call truncate_inode_pages.
   *
   * invalidate_mapping_pages() will not block on IO activity. It will not
   * invalidate pages which are dirty, locked, under writeback or mapped into
   * pagetables.
   *
   * Return: the number of the pages that were invalidated
   */
  unsigned long invalidate_mapping_pages(struct address_space *mapping,
  		pgoff_t start, pgoff_t end)
  {
  	pgoff_t indices[PAGEVEC_SIZE];
  	struct pagevec pvec;
  	pgoff_t index = start;
  	unsigned long ret;
  	unsigned long count = 0;
  	int i;
  
  	pagevec_init(&pvec);
  	while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
  			indices)) {
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  
  			/* We rely upon deletion not changing page->index */
  			index = indices[i];
  			if (index > end)
  				break;
  
  			if (xa_is_value(page)) {
  				invalidate_exceptional_entry(mapping, index,
  							     page);
  				continue;
  			}
  
  			if (!trylock_page(page))
  				continue;
  
  			WARN_ON(page_to_index(page) != index);
  
  			/* Middle of THP: skip */
  			if (PageTransTail(page)) {
  				unlock_page(page);
  				continue;
  			} else if (PageTransHuge(page)) {
  				index += HPAGE_PMD_NR - 1;
  				i += HPAGE_PMD_NR - 1;
  				/*
  				 * 'end' is in the middle of THP. Don't
  				 * invalidate the page as the part outside of
  				 * 'end' could be still useful.
  				 */
  				if (index > end) {
  					unlock_page(page);
  					continue;
  				}
  			}
  
  			ret = invalidate_inode_page(page);
  			unlock_page(page);
  			/*
  			 * Invalidation is a hint that the page is no longer
  			 * of interest and try to speed up its reclaim.
  			 */
  			if (!ret)
  				deactivate_file_page(page);
  			count += ret;
  		}
  		pagevec_remove_exceptionals(&pvec);
  		pagevec_release(&pvec);
  		cond_resched();
  		index++;
  	}
  	return count;
  }
  EXPORT_SYMBOL(invalidate_mapping_pages);
  
  /*
   * This is like invalidate_complete_page(), except it ignores the page's
   * refcount.  We do this because invalidate_inode_pages2() needs stronger
   * invalidation guarantees, and cannot afford to leave pages behind because
   * shrink_page_list() has a temp ref on them, or because they're transiently
   * sitting in the lru_cache_add() pagevecs.
   */
  static int
  invalidate_complete_page2(struct address_space *mapping, struct page *page)
  {
  	unsigned long flags;
  
  	if (page->mapping != mapping)
  		return 0;
  
  	if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
  		return 0;
  
  	xa_lock_irqsave(&mapping->i_pages, flags);
  	if (PageDirty(page))
  		goto failed;
  
  	BUG_ON(page_has_private(page));
  	__delete_from_page_cache(page, NULL);
  	xa_unlock_irqrestore(&mapping->i_pages, flags);
  
  	if (mapping->a_ops->freepage)
  		mapping->a_ops->freepage(page);
  
  	put_page(page);	/* pagecache ref */
  	return 1;
  failed:
  	xa_unlock_irqrestore(&mapping->i_pages, flags);
  	return 0;
  }
  
  static int do_launder_page(struct address_space *mapping, struct page *page)
  {
  	if (!PageDirty(page))
  		return 0;
  	if (page->mapping != mapping || mapping->a_ops->launder_page == NULL)
  		return 0;
  	return mapping->a_ops->launder_page(page);
  }
  
  /**
   * invalidate_inode_pages2_range - remove range of pages from an address_space
   * @mapping: the address_space
   * @start: the page offset 'from' which to invalidate
   * @end: the page offset 'to' which to invalidate (inclusive)
   *
   * Any pages which are found to be mapped into pagetables are unmapped prior to
   * invalidation.
   *
   * Return: -EBUSY if any pages could not be invalidated.
   */
  int invalidate_inode_pages2_range(struct address_space *mapping,
  				  pgoff_t start, pgoff_t end)
  {
  	pgoff_t indices[PAGEVEC_SIZE];
  	struct pagevec pvec;
  	pgoff_t index;
  	int i;
  	int ret = 0;
  	int ret2 = 0;
  	int did_range_unmap = 0;
  
  	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
  		goto out;
  
  	pagevec_init(&pvec);
  	index = start;
  	while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
  			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
  			indices)) {
  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];
  
  			/* We rely upon deletion not changing page->index */
  			index = indices[i];
  			if (index > end)
  				break;
  
  			if (xa_is_value(page)) {
  				if (!invalidate_exceptional_entry2(mapping,
  								   index, page))
  					ret = -EBUSY;
  				continue;
  			}
  
  			lock_page(page);
  			WARN_ON(page_to_index(page) != index);
  			if (page->mapping != mapping) {
  				unlock_page(page);
  				continue;
  			}
  			wait_on_page_writeback(page);
  			if (page_mapped(page)) {
  				if (!did_range_unmap) {
  					/*
  					 * Zap the rest of the file in one hit.
  					 */
  					unmap_mapping_pages(mapping, index,
  						(1 + end - index), false);
  					did_range_unmap = 1;
  				} else {
  					/*
  					 * Just zap this page
  					 */
  					unmap_mapping_pages(mapping, index,
  								1, false);
  				}
  			}
  			BUG_ON(page_mapped(page));
  			ret2 = do_launder_page(mapping, page);
  			if (ret2 == 0) {
  				if (!invalidate_complete_page2(mapping, page))
  					ret2 = -EBUSY;
  			}
  			if (ret2 < 0)
  				ret = ret2;
  			unlock_page(page);
  		}
  		pagevec_remove_exceptionals(&pvec);
  		pagevec_release(&pvec);
  		cond_resched();
  		index++;
  	}
  	/*
  	 * For DAX we invalidate page tables after invalidating page cache.  We
  	 * could invalidate page tables while invalidating each entry however
  	 * that would be expensive. And doing range unmapping before doesn't
  	 * work as we have no cheap way to find whether page cache entry didn't
  	 * get remapped later.
  	 */
  	if (dax_mapping(mapping)) {
  		unmap_mapping_pages(mapping, start, end - start + 1, false);
  	}
  out:
  	cleancache_invalidate_inode(mapping);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
  
  /**
   * invalidate_inode_pages2 - remove all pages from an address_space
   * @mapping: the address_space
   *
   * Any pages which are found to be mapped into pagetables are unmapped prior to
   * invalidation.
   *
   * Return: -EBUSY if any pages could not be invalidated.
   */
  int invalidate_inode_pages2(struct address_space *mapping)
  {
  	return invalidate_inode_pages2_range(mapping, 0, -1);
  }
  EXPORT_SYMBOL_GPL(invalidate_inode_pages2);
  
  /**
   * truncate_pagecache - unmap and remove pagecache that has been truncated
   * @inode: inode
   * @newsize: new file size
   *
   * inode's new i_size must already be written before truncate_pagecache
   * is called.
   *
   * This function should typically be called before the filesystem
   * releases resources associated with the freed range (eg. deallocates
   * blocks). This way, pagecache will always stay logically coherent
   * with on-disk format, and the filesystem would not have to deal with
   * situations such as writepage being called for a page that has already
   * had its underlying blocks deallocated.
   */
  void truncate_pagecache(struct inode *inode, loff_t newsize)
  {
  	struct address_space *mapping = inode->i_mapping;
  	loff_t holebegin = round_up(newsize, PAGE_SIZE);
  
  	/*
  	 * unmap_mapping_range is called twice, first simply for
  	 * efficiency so that truncate_inode_pages does fewer
  	 * single-page unmaps.  However after this first call, and
  	 * before truncate_inode_pages finishes, it is possible for
  	 * private pages to be COWed, which remain after
  	 * truncate_inode_pages finishes, hence the second
  	 * unmap_mapping_range call must be made for correctness.
  	 */
  	unmap_mapping_range(mapping, holebegin, 0, 1);
  	truncate_inode_pages(mapping, newsize);
  	unmap_mapping_range(mapping, holebegin, 0, 1);
  }
  EXPORT_SYMBOL(truncate_pagecache);
  
  /**
   * truncate_setsize - update inode and pagecache for a new file size
   * @inode: inode
   * @newsize: new file size
   *
   * truncate_setsize updates i_size and performs pagecache truncation (if
   * necessary) to @newsize. It will be typically be called from the filesystem's
   * setattr function when ATTR_SIZE is passed in.
   *
   * Must be called with a lock serializing truncates and writes (generally
   * i_mutex but e.g. xfs uses a different lock) and before all filesystem
   * specific block truncation has been performed.
   */
  void truncate_setsize(struct inode *inode, loff_t newsize)
  {
  	loff_t oldsize = inode->i_size;
  
  	i_size_write(inode, newsize);
  	if (newsize > oldsize)
  		pagecache_isize_extended(inode, oldsize, newsize);
  	truncate_pagecache(inode, newsize);
  }
  EXPORT_SYMBOL(truncate_setsize);
  
  /**
   * pagecache_isize_extended - update pagecache after extension of i_size
   * @inode:	inode for which i_size was extended
   * @from:	original inode size
   * @to:		new inode size
   *
   * Handle extension of inode size either caused by extending truncate or by
   * write starting after current i_size. We mark the page straddling current
   * i_size RO so that page_mkwrite() is called on the nearest write access to
   * the page.  This way filesystem can be sure that page_mkwrite() is called on
   * the page before user writes to the page via mmap after the i_size has been
   * changed.
   *
   * The function must be called after i_size is updated so that page fault
   * coming after we unlock the page will already see the new i_size.
   * The function must be called while we still hold i_mutex - this not only
   * makes sure i_size is stable but also that userspace cannot observe new
   * i_size value before we are prepared to store mmap writes at new inode size.
   */
  void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)
  {
  	int bsize = i_blocksize(inode);
  	loff_t rounded_from;
  	struct page *page;
  	pgoff_t index;
  
  	WARN_ON(to > inode->i_size);
  
  	if (from >= to || bsize == PAGE_SIZE)
  		return;
  	/* Page straddling @from will not have any hole block created? */
  	rounded_from = round_up(from, bsize);
  	if (to <= rounded_from || !(rounded_from & (PAGE_SIZE - 1)))
  		return;
  
  	index = from >> PAGE_SHIFT;
  	page = find_lock_page(inode->i_mapping, index);
  	/* Page not cached? Nothing to do */
  	if (!page)
  		return;
  	/*
  	 * See clear_page_dirty_for_io() for details why set_page_dirty()
  	 * is needed.
  	 */
  	if (page_mkclean(page))
  		set_page_dirty(page);
  	unlock_page(page);
  	put_page(page);
  }
  EXPORT_SYMBOL(pagecache_isize_extended);
  
  /**
   * truncate_pagecache_range - unmap and remove pagecache that is hole-punched
   * @inode: inode
   * @lstart: offset of beginning of hole
   * @lend: offset of last byte of hole
   *
   * This function should typically be called before the filesystem
   * releases resources associated with the freed range (eg. deallocates
   * blocks). This way, pagecache will always stay logically coherent
   * with on-disk format, and the filesystem would not have to deal with
   * situations such as writepage being called for a page that has already
   * had its underlying blocks deallocated.
   */
  void truncate_pagecache_range(struct inode *inode, loff_t lstart, loff_t lend)
  {
  	struct address_space *mapping = inode->i_mapping;
  	loff_t unmap_start = round_up(lstart, PAGE_SIZE);
  	loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
  	/*
  	 * This rounding is currently just for example: unmap_mapping_range
  	 * expands its hole outwards, whereas we want it to contract the hole
  	 * inwards.  However, existing callers of truncate_pagecache_range are
  	 * doing their own page rounding first.  Note that unmap_mapping_range
  	 * allows holelen 0 for all, and we allow lend -1 for end of file.
  	 */
  
  	/*
  	 * Unlike in truncate_pagecache, unmap_mapping_range is called only
  	 * once (before truncating pagecache), and without "even_cows" flag:
  	 * hole-punching should not remove private COWed pages from the hole.
  	 */
  	if ((u64)unmap_end > (u64)unmap_start)
  		unmap_mapping_range(mapping, unmap_start,
  				    1 + unmap_end - unmap_start, 0);
  	truncate_inode_pages_range(mapping, lstart, lend);
  }
  EXPORT_SYMBOL(truncate_pagecache_range);
  