page fault scalability (ext3, ext4, xfs)

[David Lang]

On Wed, 14 Aug 2013, Andy Lutomirski wrote:

>> The big problem with this approach is that not doing the
>> timestamp update on page faults is going to break the inode change
>> version counting because for ext4, btrfs and XFS it takes a
>> transaction to bump that counter. NFS needs to know the moment a
>> file is changed in memory, not when it is written to disk. Also, NFS
>> requires the change to the counter to be persistent over server
>> failures, so it needs to be changed as part of a transaction....
>
> NFS can do whatever it wants, although I suspect that even NFS can get
> away with deferring cmtime updates.

NFS already has to do syncs to make sure the data is safe on disk, have a flag 
that NFS can use to make the ctime safe, everyone else can get the performance 
improvement and NFS can have it's slow-but-safe approach.

David Lang