Re: [RFC] relaxed barrier semantics

[Christoph Hellwig <hch@lst.de>]

On Mon, Aug 02, 2010 at 11:01:53PM +0400, Vladislav Bolkhovitin wrote:
> IMHO, all is needed are:

What we need first is a simple interface that

 a) guarantees data integrity
 b) doesn't cause massive slowdowns

and then we can optimize it later.

What we absolutely don't need is a large number of different
interfaces that no one understands and that all are buggy in some way.

> >Now the fsync in XFS looks like this:
> >
> >1) write out all the data blocks using WRITE
> >2) wait for these to finish
> >3) propagate any I/O error to the inode so we can pick them up
> >4) update the inode size in the shadow in-memory structure
> >5) start a transaction to log the inode size
> >6) flush the write cache to make sure the data really is on disk
> 
> Here should be "6.1) wait for it to finish"

yes

> which can be eliminated if 
> requests sent ordered, correct?

not really - if the cache flush returns we shouldn't even send the log
update.