On Mon, 2008-09-22 at 10:04 -0700, Aaron Straus wrote:
> Here is the crux. It was possible previously but unlikely e.g. our app
> never saw this behavior. The new writeout semantics causes visible
> holes in files often.
>
> Anyway, I agree the new writeout semantics are allowed and possibly
> saner than the previous writeout path. The problem is that it is
> __annoying__ for this use case (log files).
There is always the option of using syslog.
> I'm not sure if there is an easy solution. We want the VM to writeout
> the address space in order. Maybe we can start the scan for dirty
> pages at the last page we wrote out i.e. page 0 in the example above?
You can never guarantee that in a multi-threaded environment.
Two threads may, for instance, force 2 competing fsync() calls: that
again may cause out-of-order writes.
...and even if the client doesn't reorder the writes, the _server_ may
do it, since multiple nfsd threads may race when processing writes to
the same file.
Anyway, the patch to force a single threaded nfs client to write out the
data in order is trivial. See attachment...
Trond
--- Begin Message ---
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
---
fs/nfs/write.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 3229e21..eb6b211 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1428,7 +1428,8 @@ static int nfs_write_mapping(struct address_space *mapping, int how)
.sync_mode = WB_SYNC_NONE,
.nr_to_write = LONG_MAX,
.for_writepages = 1,
- .range_cyclic = 1,
+ .range_start = 0,
+ .range_end = LLONG_MAX,
};
int ret;
--- End Message ---
