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Commit 623e3db9 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm for fs: add truncate_pagecache_range() 



Holepunching filesystems ext4 and xfs are using truncate_inode_pages_range
but forgetting to unmap pages first (ocfs2 remembers).  This is not really
a bug, since races already require truncate_inode_page() to handle that
case once the page is locked; but it can be very inefficient if the file
being punched happens to be mapped into many vmas.

Provide a drop-in replacement truncate_pagecache_range() which does the
unmapping pass first, handling the awkward mismatch between arguments to
truncate_inode_pages_range() and arguments to unmap_mapping_range().

Note that holepunching does not unmap privately COWed pages in the range:
POSIX requires that we do so when truncating, but it's hard to justify,
difficult to implement without an i_size cutoff, and no filesystem is
attempting to implement it.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Ben Myers <bpm@sgi.com>
Cc: Alex Elder <elder@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3748b2f1

include/linux/mm.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -954,7 +954,7 @@ extern void truncate_pagecache(struct inode *inode, loff_t old, loff_t new); 
extern void truncate_setsize(struct inode *inode, loff_t newsize);

extern void truncate_setsize(struct inode *inode, loff_t newsize);

extern int vmtruncate(struct inode *inode, loff_t offset);

extern int vmtruncate(struct inode *inode, loff_t offset);

extern int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end);

extern int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end);



void truncate_pagecache_range(struct inode *inode, loff_t offset, loff_t end);

int truncate_inode_page(struct address_space *mapping, struct page *page);

int truncate_inode_page(struct address_space *mapping, struct page *page);

int generic_error_remove_page(struct address_space *mapping, struct page *page);

int generic_error_remove_page(struct address_space *mapping, struct page *page);

mm/truncate.c

+40 −0
Original line number Original line Diff line number Diff line
@@ -626,3 +626,43 @@ int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend) 




	return 0;

	return 0;

}

}



/**

 * 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; and truncate_inode_pages_range

	 * currently BUGs if lend is not pagealigned-1 (it handles partial

	 * page at start of hole, but not partial page at end of hole).  Note

	 * unmap_mapping_range allows holelen 0 for all, and we allow lend -1.

	 */



	/*

	 * 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);