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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> |
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