Merge tag 'bitmap-5.17-rc1' of git://github.com/norov/linux

[linux-2.6-microblaze.git] / mm / truncate.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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/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);
}

static void clear_shadow_entry(struct address_space *mapping, pgoff_t index,
                               void *entry)
{
        spin_lock(&mapping->host->i_lock);
        xa_lock_irq(&mapping->i_pages);
        __clear_shadow_entry(mapping, index, entry);
        xa_unlock_irq(&mapping->i_pages);
        if (mapping_shrinkable(mapping))
                inode_add_lru(mapping->host);
        spin_unlock(&mapping->host->i_lock);
}

/*
 * Unconditionally remove exceptional entries. Usually called from truncate
 * path. Note that the folio_batch may be altered by this function by removing
 * exceptional entries similar to what folio_batch_remove_exceptionals() does.
 */
static void truncate_folio_batch_exceptionals(struct address_space *mapping,
                                struct folio_batch *fbatch, pgoff_t *indices)
{
        int i, j;
        bool dax;

        /* Handled by shmem itself */
        if (shmem_mapping(mapping))
                return;

        for (j = 0; j < folio_batch_count(fbatch); j++)
                if (xa_is_value(fbatch->folios[j]))
                        break;

        if (j == folio_batch_count(fbatch))
                return;

        dax = dax_mapping(mapping);
        if (!dax) {
                spin_lock(&mapping->host->i_lock);
                xa_lock_irq(&mapping->i_pages);
        }

        for (i = j; i < folio_batch_count(fbatch); i++) {
                struct folio *folio = fbatch->folios[i];
                pgoff_t index = indices[i];

                if (!xa_is_value(folio)) {
                        fbatch->folios[j++] = folio;
                        continue;
                }

                if (unlikely(dax)) {
                        dax_delete_mapping_entry(mapping, index);
                        continue;
                }

                __clear_shadow_entry(mapping, index, folio);
        }

        if (!dax) {
                xa_unlock_irq(&mapping->i_pages);
                if (mapping_shrinkable(mapping))
                        inode_add_lru(mapping->host);
                spin_unlock(&mapping->host->i_lock);
        }
        fbatch->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 bail 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_folio(struct folio *folio)
{
        if (folio_mapped(folio))
                unmap_mapping_folio(folio);

        if (folio_has_private(folio))
                do_invalidatepage(&folio->page, 0, folio_size(folio));

        /*
         * 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.
         */
        folio_cancel_dirty(folio);
        folio_clear_mappedtodisk(folio);
}

/*
 * 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)
{

        if (page->mapping != mapping)
                return 0;

        if (page_has_private(page) && !try_to_release_page(page, 0))
                return 0;

        return remove_mapping(mapping, page);
}

int truncate_inode_folio(struct address_space *mapping, struct folio *folio)
{
        if (folio->mapping != mapping)
                return -EIO;

        truncate_cleanup_folio(folio);
        filemap_remove_folio(folio);
        return 0;
}

/*
 * Handle partial folios.  The folio may be entirely within the
 * range if a split has raced with us.  If not, we zero the part of the
 * folio that's within the [start, end] range, and then split the folio if
 * it's large.  split_page_range() will discard pages which now lie beyond
 * i_size, and we rely on the caller to discard pages which lie within a
 * newly created hole.
 *
 * Returns false if splitting failed so the caller can avoid
 * discarding the entire folio which is stubbornly unsplit.
 */
bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
{
        loff_t pos = folio_pos(folio);
        unsigned int offset, length;

        if (pos < start)
                offset = start - pos;
        else
                offset = 0;
        length = folio_size(folio);
        if (pos + length <= (u64)end)
                length = length - offset;
        else
                length = end + 1 - pos - offset;

        folio_wait_writeback(folio);
        if (length == folio_size(folio)) {
                truncate_inode_folio(folio->mapping, folio);
                return true;
        }

        /*
         * We may be zeroing pages we're about to discard, but it avoids
         * doing a complex calculation here, and then doing the zeroing
         * anyway if the page split fails.
         */
        folio_zero_range(folio, offset, length);

        if (folio_has_private(folio))
                do_invalidatepage(&folio->page, offset, length);
        if (!folio_test_large(folio))
                return true;
        if (split_huge_page(&folio->page) == 0)
                return true;
        if (folio_test_dirty(folio))
                return false;
        truncate_inode_folio(folio->mapping, folio);
        return true;
}

/*
 * Used to get rid of pages on hardware memory corruption.
 */
int generic_error_remove_page(struct address_space *mapping, struct page *page)
{
        VM_BUG_ON_PAGE(PageTail(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_folio(mapping, page_folio(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 */
        struct folio_batch fbatch;
        pgoff_t         indices[PAGEVEC_SIZE];
        pgoff_t         index;
        int             i;
        struct folio    *folio;
        bool            same_folio;

        if (mapping_empty(mapping))
                return;

        /*
         * '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;

        folio_batch_init(&fbatch);
        index = start;
        while (index < end && find_lock_entries(mapping, index, end - 1,
                        &fbatch, indices)) {
                index = indices[folio_batch_count(&fbatch) - 1] + 1;
                truncate_folio_batch_exceptionals(mapping, &fbatch, indices);
                for (i = 0; i < folio_batch_count(&fbatch); i++)
                        truncate_cleanup_folio(fbatch.folios[i]);
                delete_from_page_cache_batch(mapping, &fbatch);
                for (i = 0; i < folio_batch_count(&fbatch); i++)
                        folio_unlock(fbatch.folios[i]);
                folio_batch_release(&fbatch);
                cond_resched();
        }

        same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
        folio = __filemap_get_folio(mapping, lstart >> PAGE_SHIFT, FGP_LOCK, 0);
        if (folio) {
                same_folio = lend < folio_pos(folio) + folio_size(folio);
                if (!truncate_inode_partial_folio(folio, lstart, lend)) {
                        start = folio->index + folio_nr_pages(folio);
                        if (same_folio)
                                end = folio->index;
                }
                folio_unlock(folio);
                folio_put(folio);
                folio = NULL;
        }

        if (!same_folio)
                folio = __filemap_get_folio(mapping, lend >> PAGE_SHIFT,
                                                FGP_LOCK, 0);
        if (folio) {
                if (!truncate_inode_partial_folio(folio, lstart, lend))
                        end = folio->index;
                folio_unlock(folio);
                folio_put(folio);
        }

        index = start;
        while (index < end) {
                cond_resched();
                if (!find_get_entries(mapping, index, end - 1, &fbatch,
                                indices)) {
                        /* If all gone from start onwards, we're done */
                        if (index == start)
                                break;
                        /* Otherwise restart to make sure all gone */
                        index = start;
                        continue;
                }

                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        struct folio *folio = fbatch.folios[i];

                        /* We rely upon deletion not changing page->index */
                        index = indices[i];

                        if (xa_is_value(folio))
                                continue;

                        folio_lock(folio);
                        VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
                        folio_wait_writeback(folio);
                        truncate_inode_folio(mapping, folio);
                        folio_unlock(folio);
                        index = folio_index(folio) + folio_nr_pages(folio) - 1;
                }
                truncate_folio_batch_exceptionals(mapping, &fbatch, indices);
                folio_batch_release(&fbatch);
                index++;
        }
}
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_rwsem and
 * mapping->invalidate_lock.
 *
 * 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_rwsem.
 *
 * 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)
{
        /*
         * 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);

        if (!mapping_empty(mapping)) {
                /*
                 * 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);
        }

        truncate_inode_pages(mapping, 0);
}
EXPORT_SYMBOL(truncate_inode_pages_final);

static unsigned long __invalidate_mapping_pages(struct address_space *mapping,
                pgoff_t start, pgoff_t end, unsigned long *nr_pagevec)
{
        pgoff_t indices[PAGEVEC_SIZE];
        struct folio_batch fbatch;
        pgoff_t index = start;
        unsigned long ret;
        unsigned long count = 0;
        int i;

        folio_batch_init(&fbatch);
        while (find_lock_entries(mapping, index, end, &fbatch, indices)) {
                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        struct page *page = &fbatch.folios[i]->page;

                        /* We rely upon deletion not changing page->index */
                        index = indices[i];

                        if (xa_is_value(page)) {
                                count += invalidate_exceptional_entry(mapping,
                                                                      index,
                                                                      page);
                                continue;
                        }
                        index += thp_nr_pages(page) - 1;

                        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);
                                /* It is likely on the pagevec of a remote CPU */
                                if (nr_pagevec)
                                        (*nr_pagevec)++;
                        }
                        count += ret;
                }
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);
                cond_resched();
                index++;
        }
        return count;
}

/**
 * invalidate_mapping_pages - Invalidate all clean, unlocked cache of one inode
 * @mapping: the address_space which holds the cache to invalidate
 * @start: the offset 'from' which to invalidate
 * @end: the offset 'to' which to invalidate (inclusive)
 *
 * This function removes pages that are clean, unmapped and unlocked,
 * as well as shadow entries. It will not block on IO activity.
 *
 * If you want to remove all the pages of one inode, regardless of
 * their use and writeback state, use truncate_inode_pages().
 *
 * Return: the number of the cache entries that were invalidated
 */
unsigned long invalidate_mapping_pages(struct address_space *mapping,
                pgoff_t start, pgoff_t end)
{
        return __invalidate_mapping_pages(mapping, start, end, NULL);
}
EXPORT_SYMBOL(invalidate_mapping_pages);

/**
 * invalidate_mapping_pagevec - 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)
 * @nr_pagevec: invalidate failed page number for caller
 *
 * This helper is similar to invalidate_mapping_pages(), except that it accounts
 * for pages that are likely on a pagevec and counts them in @nr_pagevec, which
 * will be used by the caller.
 */
void invalidate_mapping_pagevec(struct address_space *mapping,
                pgoff_t start, pgoff_t end, unsigned long *nr_pagevec)
{
        __invalidate_mapping_pages(mapping, start, end, nr_pagevec);
}

/*
 * 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_folio2(struct address_space *mapping,
                                        struct folio *folio)
{
        if (folio->mapping != mapping)
                return 0;

        if (folio_has_private(folio) &&
            !filemap_release_folio(folio, GFP_KERNEL))
                return 0;

        spin_lock(&mapping->host->i_lock);
        xa_lock_irq(&mapping->i_pages);
        if (folio_test_dirty(folio))
                goto failed;

        BUG_ON(folio_has_private(folio));
        __filemap_remove_folio(folio, NULL);
        xa_unlock_irq(&mapping->i_pages);
        if (mapping_shrinkable(mapping))
                inode_add_lru(mapping->host);
        spin_unlock(&mapping->host->i_lock);

        filemap_free_folio(mapping, folio);
        return 1;
failed:
        xa_unlock_irq(&mapping->i_pages);
        spin_unlock(&mapping->host->i_lock);
        return 0;
}

static int do_launder_folio(struct address_space *mapping, struct folio *folio)
{
        if (!folio_test_dirty(folio))
                return 0;
        if (folio->mapping != mapping || mapping->a_ops->launder_page == NULL)
                return 0;
        return mapping->a_ops->launder_page(&folio->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 folio_batch fbatch;
        pgoff_t index;
        int i;
        int ret = 0;
        int ret2 = 0;
        int did_range_unmap = 0;

        if (mapping_empty(mapping))
                return 0;

        folio_batch_init(&fbatch);
        index = start;
        while (find_get_entries(mapping, index, end, &fbatch, indices)) {
                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        struct folio *folio = fbatch.folios[i];

                        /* We rely upon deletion not changing folio->index */
                        index = indices[i];

                        if (xa_is_value(folio)) {
                                if (!invalidate_exceptional_entry2(mapping,
                                                index, folio))
                                        ret = -EBUSY;
                                continue;
                        }

                        if (!did_range_unmap && folio_mapped(folio)) {
                                /*
                                 * If folio is mapped, before taking its lock,
                                 * zap the rest of the file in one hit.
                                 */
                                unmap_mapping_pages(mapping, index,
                                                (1 + end - index), false);
                                did_range_unmap = 1;
                        }

                        folio_lock(folio);
                        VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
                        if (folio->mapping != mapping) {
                                folio_unlock(folio);
                                continue;
                        }
                        folio_wait_writeback(folio);

                        if (folio_mapped(folio))
                                unmap_mapping_folio(folio);
                        BUG_ON(folio_mapped(folio));

                        ret2 = do_launder_folio(mapping, folio);
                        if (ret2 == 0) {
                                if (!invalidate_complete_folio2(mapping, folio))
                                        ret2 = -EBUSY;
                        }
                        if (ret2 < 0)
                                ret = ret2;
                        folio_unlock(folio);
                }
                folio_batch_remove_exceptionals(&fbatch);
                folio_batch_release(&fbatch);
                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);
        }
        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_rwsem 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_rwsem - 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);