[PATCH v2 0/3] Rework mtime and ctime updates on mmaped writes

From: Andy Lutomirski
Date: Fri Dec 21 2012 - 16:29:16 EST

Writes via mmap currently update mtime and ctime in ->page_mkwrite.
This is unfortunate from a performance and a correctness point of view.
The file times should be updated after writes, not before (so that every
write eventually results in a fresh timestamp). This is needed for
POSIX compliance. More importantly (for me), ->page_mkwrite is called
periodically even on mlocked pages, and some filesystems can sleep in

This patchset attempts to fix both issues at once. It adds a new
address_space flag AS_CMTIME that is set atomically whenever the system
transfers a pte dirty bit to a struct page backed by the address_space.
This can happen with various locks held and when low on memory.

Later on, whenever syncing an inode (which happens indirectly in msync)
or whenever a vma is torn down, if AS_CMTIME is set, then the file times
are updated. This happens in a context from which (I think) it's safe
to dirty inodes.

One nice property of this approach is that it requires no fs-specific
work. It's actually quite a bit simpler than I expected.

I've tested this, and mtime and ctime are updated on munmap, exit, MS_SYNC,
and fsync after writing via mmap. The times are also updated 30 seconds
after writing, all by themselves :) xfstest #215 also passes.Lockdep has
no complaints.

Changes from v1:
- inode_update_time_writable now locks against the fs freezer
- Minor cleanups
- Major changelog improvements

Andy Lutomirski (3):
mm: Explicitly track when the page dirty bit is transferred from a
mm: Update file times when inodes are written after mmaped writes
Remove file_update_time from all mkwrite paths

fs/9p/vfs_file.c | 3 ---
fs/btrfs/inode.c | 4 +--
fs/buffer.c | 6 -----
fs/ceph/addr.c | 3 ---
fs/ext4/inode.c | 1 -
fs/gfs2/file.c | 3 ---
fs/inode.c | 72 ++++++++++++++++++++++++++++++++++++++-----------
fs/nilfs2/file.c | 1 -
fs/sysfs/bin.c | 2 --
include/linux/fs.h | 1 +
include/linux/mm.h | 1 +
include/linux/pagemap.h | 3 +++
mm/filemap.c | 1 -
mm/memory-failure.c | 4 +--
mm/memory.c | 5 +---
mm/mmap.c | 4 +++
mm/page-writeback.c | 42 +++++++++++++++++++++++++++--
mm/rmap.c | 9 ++++---
18 files changed, 115 insertions(+), 50 deletions(-)


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