[Ocfs2-users] Shared writable mmap

[Joel Becker]

On Wed, Jan 07, 2009 at 01:32:14PM +0200, Eran Maman wrote:
> I would like to know more about the ocfs2 implementation for shared
> writable mmap.
> 
> Does every read go to the disk? Or is it cached to RAM memory?

	Like all mmap operations, the data is cached in RAM as long as
it is unmodified.  Basically, all local node operations behave like an
un-clustered filesystem.  The only change is when another node needs
something.  If the local node has a cached page and a remote node wants
to change that page, the local node will drop the page and re-read it
later.  Conversely, if the local node has a modified page and the remote
node wants to read that page, the local node will write the changes to
disk.
	I hope that answers your question.

Joel

-- 

Viro's Razor:
	Any race condition, no matter how unlikely, will occur just
	often enough to bite you.

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127