Author: Andrew Morton <[EMAIL PROTECTED]>
AuthorDate: Tue Oct 16 23:30:37 2007 -0700
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed Oct 17 08:43:02 2007 -0700
writeback: fix time ordering of the per superblock dirty inode lists 6
Recycling the previous changelog:
When the writeback function is operating in writeback-for-flushing mode
(as opposed to writeback-for-integrity) and it encounters an I_LOCKed
it will skip writing that inode. This is done for throughput and latency:
move on to another inode rather than blocking for this one.
Writeback skips this inode by moving it off s_io and onto s_dirty, so that
writeback can proceed with the other inodes on s_io.
However that inode movement can corrupt s_dirty's
reverse-time-orderedness. Fix that by using the new redirty_tail(), which
will update the refiled inode's dirtied_when field.
Note: the behaviour in here is a bit rude: if kupdate happens to come
across a locked inode then it will defer writeback of that inode for
30 seconds. We'll address that in the next patch.
Address that here. What we do is to move the skipped inode to the _head_ of
s_dirty, immediately eligible for writeout again. Instead of deferring that
writeout for another 30 seconds.
One would think that this might cause a livelock: we keep on trying to write
the same locked inode. But it won't because:
a) if that was the case, it would _already_ be happening on the
balance_dirty_pages codepath. Because balance_dirty_pages() doesn't care
about inode timestamps.
b) if we skipped this inode then we won't have done any writeback. The
higher-level writeback paths will see that wbc.nr_to_write didn't change
and they'll then back off and take a nap.
Cc: Mike Waychison <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
fs/fs-writeback.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1b43cc9..30d9383 100644
@@ -308,7 +308,14 @@ __writeback_single_inode(struct inode *inode, struct
struct address_space *mapping = inode->i_mapping;
+ * We're skipping this inode because it's locked, and we're not
+ * doing writeback-for-data-integrity. Move it to the head of
+ * s_dirty so that writeback can proceed with the other inodes
+ * on s_io. We'll have another go at writing back this inode
+ * when the s_dirty iodes get moved back onto s_io.
* Even if we don't actually write the inode itself here,
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