On Fri, Aug 21, 2009 at 03:45:18PM -0700, Joel Becker wrote:
quoted text
> On Fri, Aug 21, 2009 at 06:08:52PM -0400, Theodore Tso wrote:
> > http://ext4.wiki.kernel.org/index.php/Clarifying_Direct_IO's_Semantics
> > 
> > Comments are welcome, either on the wiki's talk page, or directly to
> > me, or to the linux-fsdevel or linux-ext4.
> 
> 	In the section on perhaps not waiting for buffered fallback, we
> need to clarify that O_DIRECT reads need to know to look in the
> pagecache.  That is, if we decide that extending O_DIRECT writes without
> fsync can return before the data hits the storage, the caller shouldn't
> also have to call fsync() just to call read() of data they just wrote!

Yeah, I guess we can only do that if the filesystem guarantees
coherence between the page cache and O_DIRECT reads; it's been a long
while since I've studied that code, so I'm not sure whether all
filesystems that support O_DIRECT provide this coherency (since I
thought it was provided in the generic O_DIRECT routines, isn't it?)
or not.

							- Ted
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