2 * fs/dax.c - Direct Access filesystem code
3 * Copyright (c) 2013-2014 Intel Corporation
4 * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
5 * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
7 * This program is free software; you can redistribute it and/or modify it
8 * under the terms and conditions of the GNU General Public License,
9 * version 2, as published by the Free Software Foundation.
11 * This program is distributed in the hope it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
17 #include <linux/atomic.h>
18 #include <linux/blkdev.h>
19 #include <linux/buffer_head.h>
20 #include <linux/dax.h>
22 #include <linux/genhd.h>
23 #include <linux/highmem.h>
24 #include <linux/memcontrol.h>
26 #include <linux/mutex.h>
27 #include <linux/pmem.h>
28 #include <linux/sched.h>
29 #include <linux/uio.h>
30 #include <linux/vmstat.h>
31 #include <linux/sizes.h>
33 static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
35 struct request_queue *q = bdev->bd_queue;
38 dax->addr = (void __pmem *) ERR_PTR(-EIO);
39 if (blk_queue_enter(q, true) != 0)
42 rc = bdev_direct_access(bdev, dax);
44 dax->addr = (void __pmem *) ERR_PTR(rc);
51 static void dax_unmap_atomic(struct block_device *bdev,
52 const struct blk_dax_ctl *dax)
54 if (IS_ERR(dax->addr))
56 blk_queue_exit(bdev->bd_queue);
60 * dax_clear_blocks() is called from within transaction context from XFS,
61 * and hence this means the stack from this point must follow GFP_NOFS
62 * semantics for all operations.
64 int dax_clear_blocks(struct inode *inode, sector_t block, long _size)
66 struct block_device *bdev = inode->i_sb->s_bdev;
67 struct blk_dax_ctl dax = {
68 .sector = block << (inode->i_blkbits - 9),
76 count = dax_map_atomic(bdev, &dax);
79 sz = min_t(long, count, SZ_128K);
80 clear_pmem(dax.addr, sz);
82 dax.sector += sz / 512;
83 dax_unmap_atomic(bdev, &dax);
90 EXPORT_SYMBOL_GPL(dax_clear_blocks);
92 /* the clear_pmem() calls are ordered by a wmb_pmem() in the caller */
93 static void dax_new_buf(void __pmem *addr, unsigned size, unsigned first,
94 loff_t pos, loff_t end)
96 loff_t final = end - pos + first; /* The final byte of the buffer */
99 clear_pmem(addr, first);
101 clear_pmem(addr + final, size - final);
104 static bool buffer_written(struct buffer_head *bh)
106 return buffer_mapped(bh) && !buffer_unwritten(bh);
110 * When ext4 encounters a hole, it returns without modifying the buffer_head
111 * which means that we can't trust b_size. To cope with this, we set b_state
112 * to 0 before calling get_block and, if any bit is set, we know we can trust
113 * b_size. Unfortunate, really, since ext4 knows precisely how long a hole is
114 * and would save us time calling get_block repeatedly.
116 static bool buffer_size_valid(struct buffer_head *bh)
118 return bh->b_state != 0;
122 static sector_t to_sector(const struct buffer_head *bh,
123 const struct inode *inode)
125 sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
130 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
131 loff_t start, loff_t end, get_block_t get_block,
132 struct buffer_head *bh)
134 loff_t pos = start, max = start, bh_max = start;
135 bool hole = false, need_wmb = false;
136 struct block_device *bdev = NULL;
137 int rw = iov_iter_rw(iter), rc;
139 struct blk_dax_ctl dax = {
140 .addr = (void __pmem *) ERR_PTR(-EIO),
144 end = min(end, i_size_read(inode));
149 unsigned blkbits = inode->i_blkbits;
150 long page = pos >> PAGE_SHIFT;
151 sector_t block = page << (PAGE_SHIFT - blkbits);
152 unsigned first = pos - (block << blkbits);
156 bh->b_size = PAGE_ALIGN(end - pos);
158 rc = get_block(inode, block, bh, rw == WRITE);
161 if (!buffer_size_valid(bh))
162 bh->b_size = 1 << blkbits;
163 bh_max = pos - first + bh->b_size;
166 unsigned done = bh->b_size -
167 (bh_max - (pos - first));
168 bh->b_blocknr += done >> blkbits;
172 hole = rw == READ && !buffer_written(bh);
174 size = bh->b_size - first;
176 dax_unmap_atomic(bdev, &dax);
177 dax.sector = to_sector(bh, inode);
178 dax.size = bh->b_size;
179 map_len = dax_map_atomic(bdev, &dax);
184 if (buffer_unwritten(bh) || buffer_new(bh)) {
185 dax_new_buf(dax.addr, map_len, first,
190 size = map_len - first;
192 max = min(pos + size, end);
195 if (iov_iter_rw(iter) == WRITE) {
196 len = copy_from_iter_pmem(dax.addr, max - pos, iter);
199 len = copy_to_iter((void __force *) dax.addr, max - pos,
202 len = iov_iter_zero(max - pos, iter);
210 if (!IS_ERR(dax.addr))
216 dax_unmap_atomic(bdev, &dax);
218 return (pos == start) ? rc : pos - start;
222 * dax_do_io - Perform I/O to a DAX file
223 * @iocb: The control block for this I/O
224 * @inode: The file which the I/O is directed at
225 * @iter: The addresses to do I/O from or to
226 * @pos: The file offset where the I/O starts
227 * @get_block: The filesystem method used to translate file offsets to blocks
228 * @end_io: A filesystem callback for I/O completion
231 * This function uses the same locking scheme as do_blockdev_direct_IO:
232 * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
233 * caller for writes. For reads, we take and release the i_mutex ourselves.
234 * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
235 * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
238 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
239 struct iov_iter *iter, loff_t pos, get_block_t get_block,
240 dio_iodone_t end_io, int flags)
242 struct buffer_head bh;
243 ssize_t retval = -EINVAL;
244 loff_t end = pos + iov_iter_count(iter);
246 memset(&bh, 0, sizeof(bh));
248 if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
249 struct address_space *mapping = inode->i_mapping;
250 mutex_lock(&inode->i_mutex);
251 retval = filemap_write_and_wait_range(mapping, pos, end - 1);
253 mutex_unlock(&inode->i_mutex);
258 /* Protects against truncate */
259 if (!(flags & DIO_SKIP_DIO_COUNT))
260 inode_dio_begin(inode);
262 retval = dax_io(inode, iter, pos, end, get_block, &bh);
264 if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
265 mutex_unlock(&inode->i_mutex);
267 if ((retval > 0) && end_io)
268 end_io(iocb, pos, retval, bh.b_private);
270 if (!(flags & DIO_SKIP_DIO_COUNT))
271 inode_dio_end(inode);
275 EXPORT_SYMBOL_GPL(dax_do_io);
278 * The user has performed a load from a hole in the file. Allocating
279 * a new page in the file would cause excessive storage usage for
280 * workloads with sparse files. We allocate a page cache page instead.
281 * We'll kick it out of the page cache if it's ever written to,
282 * otherwise it will simply fall out of the page cache under memory
283 * pressure without ever having been dirtied.
285 static int dax_load_hole(struct address_space *mapping, struct page *page,
286 struct vm_fault *vmf)
289 struct inode *inode = mapping->host;
291 page = find_or_create_page(mapping, vmf->pgoff,
292 GFP_KERNEL | __GFP_ZERO);
295 /* Recheck i_size under page lock to avoid truncate race */
296 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
297 if (vmf->pgoff >= size) {
299 page_cache_release(page);
300 return VM_FAULT_SIGBUS;
304 return VM_FAULT_LOCKED;
307 static int copy_user_bh(struct page *to, struct inode *inode,
308 struct buffer_head *bh, unsigned long vaddr)
310 struct blk_dax_ctl dax = {
311 .sector = to_sector(bh, inode),
314 struct block_device *bdev = bh->b_bdev;
317 if (dax_map_atomic(bdev, &dax) < 0)
318 return PTR_ERR(dax.addr);
319 vto = kmap_atomic(to);
320 copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
322 dax_unmap_atomic(bdev, &dax);
326 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
327 struct vm_area_struct *vma, struct vm_fault *vmf)
329 unsigned long vaddr = (unsigned long)vmf->virtual_address;
330 struct address_space *mapping = inode->i_mapping;
331 struct block_device *bdev = bh->b_bdev;
332 struct blk_dax_ctl dax = {
333 .sector = to_sector(bh, inode),
339 i_mmap_lock_read(mapping);
342 * Check truncate didn't happen while we were allocating a block.
343 * If it did, this block may or may not be still allocated to the
344 * file. We can't tell the filesystem to free it because we can't
345 * take i_mutex here. In the worst case, the file still has blocks
346 * allocated past the end of the file.
348 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
349 if (unlikely(vmf->pgoff >= size)) {
354 if (dax_map_atomic(bdev, &dax) < 0) {
355 error = PTR_ERR(dax.addr);
359 if (buffer_unwritten(bh) || buffer_new(bh)) {
360 clear_pmem(dax.addr, PAGE_SIZE);
363 dax_unmap_atomic(bdev, &dax);
365 error = vm_insert_mixed(vma, vaddr, dax.pfn);
368 i_mmap_unlock_read(mapping);
374 * __dax_fault - handle a page fault on a DAX file
375 * @vma: The virtual memory area where the fault occurred
376 * @vmf: The description of the fault
377 * @get_block: The filesystem method used to translate file offsets to blocks
378 * @complete_unwritten: The filesystem method used to convert unwritten blocks
379 * to written so the data written to them is exposed. This is required for
380 * required by write faults for filesystems that will return unwritten
381 * extent mappings from @get_block, but it is optional for reads as
382 * dax_insert_mapping() will always zero unwritten blocks. If the fs does
383 * not support unwritten extents, the it should pass NULL.
385 * When a page fault occurs, filesystems may call this helper in their
386 * fault handler for DAX files. __dax_fault() assumes the caller has done all
387 * the necessary locking for the page fault to proceed successfully.
389 int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
390 get_block_t get_block, dax_iodone_t complete_unwritten)
392 struct file *file = vma->vm_file;
393 struct address_space *mapping = file->f_mapping;
394 struct inode *inode = mapping->host;
396 struct buffer_head bh;
397 unsigned long vaddr = (unsigned long)vmf->virtual_address;
398 unsigned blkbits = inode->i_blkbits;
404 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
405 if (vmf->pgoff >= size)
406 return VM_FAULT_SIGBUS;
408 memset(&bh, 0, sizeof(bh));
409 block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
410 bh.b_size = PAGE_SIZE;
413 page = find_get_page(mapping, vmf->pgoff);
415 if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
416 page_cache_release(page);
417 return VM_FAULT_RETRY;
419 if (unlikely(page->mapping != mapping)) {
421 page_cache_release(page);
424 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
425 if (unlikely(vmf->pgoff >= size)) {
427 * We have a struct page covering a hole in the file
428 * from a read fault and we've raced with a truncate
435 error = get_block(inode, block, &bh, 0);
436 if (!error && (bh.b_size < PAGE_SIZE))
437 error = -EIO; /* fs corruption? */
441 if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
442 if (vmf->flags & FAULT_FLAG_WRITE) {
443 error = get_block(inode, block, &bh, 1);
444 count_vm_event(PGMAJFAULT);
445 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
446 major = VM_FAULT_MAJOR;
447 if (!error && (bh.b_size < PAGE_SIZE))
452 return dax_load_hole(mapping, page, vmf);
457 struct page *new_page = vmf->cow_page;
458 if (buffer_written(&bh))
459 error = copy_user_bh(new_page, inode, &bh, vaddr);
461 clear_user_highpage(new_page, vaddr);
466 i_mmap_lock_read(mapping);
467 /* Check we didn't race with truncate */
468 size = (i_size_read(inode) + PAGE_SIZE - 1) >>
470 if (vmf->pgoff >= size) {
471 i_mmap_unlock_read(mapping);
476 return VM_FAULT_LOCKED;
479 /* Check we didn't race with a read fault installing a new page */
481 page = find_lock_page(mapping, vmf->pgoff);
484 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
486 delete_from_page_cache(page);
488 page_cache_release(page);
492 * If we successfully insert the new mapping over an unwritten extent,
493 * we need to ensure we convert the unwritten extent. If there is an
494 * error inserting the mapping, the filesystem needs to leave it as
495 * unwritten to prevent exposure of the stale underlying data to
496 * userspace, but we still need to call the completion function so
497 * the private resources on the mapping buffer can be released. We
498 * indicate what the callback should do via the uptodate variable, same
499 * as for normal BH based IO completions.
501 error = dax_insert_mapping(inode, &bh, vma, vmf);
502 if (buffer_unwritten(&bh)) {
503 if (complete_unwritten)
504 complete_unwritten(&bh, !error);
506 WARN_ON_ONCE(!(vmf->flags & FAULT_FLAG_WRITE));
510 if (error == -ENOMEM)
511 return VM_FAULT_OOM | major;
512 /* -EBUSY is fine, somebody else faulted on the same PTE */
513 if ((error < 0) && (error != -EBUSY))
514 return VM_FAULT_SIGBUS | major;
515 return VM_FAULT_NOPAGE | major;
520 page_cache_release(page);
524 EXPORT_SYMBOL(__dax_fault);
527 * dax_fault - handle a page fault on a DAX file
528 * @vma: The virtual memory area where the fault occurred
529 * @vmf: The description of the fault
530 * @get_block: The filesystem method used to translate file offsets to blocks
532 * When a page fault occurs, filesystems may call this helper in their
533 * fault handler for DAX files.
535 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
536 get_block_t get_block, dax_iodone_t complete_unwritten)
539 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
541 if (vmf->flags & FAULT_FLAG_WRITE) {
542 sb_start_pagefault(sb);
543 file_update_time(vma->vm_file);
545 result = __dax_fault(vma, vmf, get_block, complete_unwritten);
546 if (vmf->flags & FAULT_FLAG_WRITE)
547 sb_end_pagefault(sb);
551 EXPORT_SYMBOL_GPL(dax_fault);
553 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
555 * The 'colour' (ie low bits) within a PMD of a page offset. This comes up
556 * more often than one might expect in the below function.
558 #define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
560 int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
561 pmd_t *pmd, unsigned int flags, get_block_t get_block,
562 dax_iodone_t complete_unwritten)
564 struct file *file = vma->vm_file;
565 struct address_space *mapping = file->f_mapping;
566 struct inode *inode = mapping->host;
567 struct buffer_head bh;
568 unsigned blkbits = inode->i_blkbits;
569 unsigned long pmd_addr = address & PMD_MASK;
570 bool write = flags & FAULT_FLAG_WRITE;
571 struct block_device *bdev;
576 /* dax pmd mappings are broken wrt gup and fork */
577 if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
578 return VM_FAULT_FALLBACK;
580 /* Fall back to PTEs if we're going to COW */
581 if (write && !(vma->vm_flags & VM_SHARED)) {
582 split_huge_pmd(vma, pmd, address);
583 return VM_FAULT_FALLBACK;
585 /* If the PMD would extend outside the VMA */
586 if (pmd_addr < vma->vm_start)
587 return VM_FAULT_FALLBACK;
588 if ((pmd_addr + PMD_SIZE) > vma->vm_end)
589 return VM_FAULT_FALLBACK;
591 pgoff = linear_page_index(vma, pmd_addr);
592 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
594 return VM_FAULT_SIGBUS;
595 /* If the PMD would cover blocks out of the file */
596 if ((pgoff | PG_PMD_COLOUR) >= size)
597 return VM_FAULT_FALLBACK;
599 memset(&bh, 0, sizeof(bh));
600 block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
602 bh.b_size = PMD_SIZE;
603 if (get_block(inode, block, &bh, write) != 0)
604 return VM_FAULT_SIGBUS;
606 i_mmap_lock_read(mapping);
609 * If the filesystem isn't willing to tell us the length of a hole,
610 * just fall back to PTEs. Calling get_block 512 times in a loop
613 if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
617 * If we allocated new storage, make sure no process has any
618 * zero pages covering this hole
620 if (buffer_new(&bh)) {
621 i_mmap_unlock_read(mapping);
622 unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
623 i_mmap_lock_read(mapping);
627 * If a truncate happened while we were allocating blocks, we may
628 * leave blocks allocated to the file that are beyond EOF. We can't
629 * take i_mutex here, so just leave them hanging; they'll be freed
630 * when the file is deleted.
632 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
634 result = VM_FAULT_SIGBUS;
637 if ((pgoff | PG_PMD_COLOUR) >= size)
640 if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {
643 struct page *zero_page = get_huge_zero_page();
645 if (unlikely(!zero_page))
648 ptl = pmd_lock(vma->vm_mm, pmd);
649 if (!pmd_none(*pmd)) {
654 entry = mk_pmd(zero_page, vma->vm_page_prot);
655 entry = pmd_mkhuge(entry);
656 set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
657 result = VM_FAULT_NOPAGE;
660 struct blk_dax_ctl dax = {
661 .sector = to_sector(&bh, inode),
664 long length = dax_map_atomic(bdev, &dax);
667 result = VM_FAULT_SIGBUS;
670 if ((length < PMD_SIZE) || (dax.pfn & PG_PMD_COLOUR)) {
671 dax_unmap_atomic(bdev, &dax);
676 * TODO: teach vmf_insert_pfn_pmd() to support
677 * 'pte_special' for pmds
679 if (pfn_valid(dax.pfn)) {
680 dax_unmap_atomic(bdev, &dax);
684 if (buffer_unwritten(&bh) || buffer_new(&bh)) {
685 clear_pmem(dax.addr, PMD_SIZE);
687 count_vm_event(PGMAJFAULT);
688 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
689 result |= VM_FAULT_MAJOR;
691 dax_unmap_atomic(bdev, &dax);
693 result |= vmf_insert_pfn_pmd(vma, address, pmd, dax.pfn, write);
697 i_mmap_unlock_read(mapping);
699 if (buffer_unwritten(&bh))
700 complete_unwritten(&bh, !(result & VM_FAULT_ERROR));
705 count_vm_event(THP_FAULT_FALLBACK);
706 result = VM_FAULT_FALLBACK;
709 EXPORT_SYMBOL_GPL(__dax_pmd_fault);
712 * dax_pmd_fault - handle a PMD fault on a DAX file
713 * @vma: The virtual memory area where the fault occurred
714 * @vmf: The description of the fault
715 * @get_block: The filesystem method used to translate file offsets to blocks
717 * When a page fault occurs, filesystems may call this helper in their
718 * pmd_fault handler for DAX files.
720 int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
721 pmd_t *pmd, unsigned int flags, get_block_t get_block,
722 dax_iodone_t complete_unwritten)
725 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
727 if (flags & FAULT_FLAG_WRITE) {
728 sb_start_pagefault(sb);
729 file_update_time(vma->vm_file);
731 result = __dax_pmd_fault(vma, address, pmd, flags, get_block,
733 if (flags & FAULT_FLAG_WRITE)
734 sb_end_pagefault(sb);
738 EXPORT_SYMBOL_GPL(dax_pmd_fault);
739 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
742 * dax_pfn_mkwrite - handle first write to DAX page
743 * @vma: The virtual memory area where the fault occurred
744 * @vmf: The description of the fault
747 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
749 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
751 sb_start_pagefault(sb);
752 file_update_time(vma->vm_file);
753 sb_end_pagefault(sb);
754 return VM_FAULT_NOPAGE;
756 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
759 * dax_zero_page_range - zero a range within a page of a DAX file
760 * @inode: The file being truncated
761 * @from: The file offset that is being truncated to
762 * @length: The number of bytes to zero
763 * @get_block: The filesystem method used to translate file offsets to blocks
765 * This function can be called by a filesystem when it is zeroing part of a
766 * page in a DAX file. This is intended for hole-punch operations. If
767 * you are truncating a file, the helper function dax_truncate_page() may be
770 * We work in terms of PAGE_CACHE_SIZE here for commonality with
771 * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
772 * took care of disposing of the unnecessary blocks. Even if the filesystem
773 * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
774 * since the file might be mmapped.
776 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
777 get_block_t get_block)
779 struct buffer_head bh;
780 pgoff_t index = from >> PAGE_CACHE_SHIFT;
781 unsigned offset = from & (PAGE_CACHE_SIZE-1);
784 /* Block boundary? Nothing to do */
787 BUG_ON((offset + length) > PAGE_CACHE_SIZE);
789 memset(&bh, 0, sizeof(bh));
790 bh.b_size = PAGE_CACHE_SIZE;
791 err = get_block(inode, index, &bh, 0);
794 if (buffer_written(&bh)) {
795 struct block_device *bdev = bh.b_bdev;
796 struct blk_dax_ctl dax = {
797 .sector = to_sector(&bh, inode),
798 .size = PAGE_CACHE_SIZE,
801 if (dax_map_atomic(bdev, &dax) < 0)
802 return PTR_ERR(dax.addr);
803 clear_pmem(dax.addr + offset, length);
805 dax_unmap_atomic(bdev, &dax);
810 EXPORT_SYMBOL_GPL(dax_zero_page_range);
813 * dax_truncate_page - handle a partial page being truncated in a DAX file
814 * @inode: The file being truncated
815 * @from: The file offset that is being truncated to
816 * @get_block: The filesystem method used to translate file offsets to blocks
818 * Similar to block_truncate_page(), this function can be called by a
819 * filesystem when it is truncating a DAX file to handle the partial page.
821 * We work in terms of PAGE_CACHE_SIZE here for commonality with
822 * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
823 * took care of disposing of the unnecessary blocks. Even if the filesystem
824 * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
825 * since the file might be mmapped.
827 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
829 unsigned length = PAGE_CACHE_ALIGN(from) - from;
830 return dax_zero_page_range(inode, from, length, get_block);
832 EXPORT_SYMBOL_GPL(dax_truncate_page);