diff options
authorHugh Dickins <hughd@google.com>2012-03-28 14:42:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-28 17:14:35 -0700
commit623e3db9f9b7d6e7b2a99180f9cf0825c936ab7a (patch)
parentprocfs: fix /proc/statm (diff)
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: Hugh 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2 files changed, 41 insertions, 1 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index cf7982336103..630068184265 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -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 int vmtruncate(struct inode *inode, loff_t offset);
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 generic_error_remove_page(struct address_space *mapping, struct page *page);
diff --git a/mm/truncate.c b/mm/truncate.c
index 18aded3a89fc..61a183b89df6 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -626,3 +626,43 @@ int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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);