On Tue, Oct 30, 2012 at 10:28:33AM +1100, NeilBrown wrote: > On Fri, 26 Oct 2012 17:06:55 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxx> > wrote: > > > From: "J. Bruce Fields" <bfields@xxxxxxxxxx> > > > > Peter pointed out to me that the nfs server is implementing stable > > writes by setting the O_SYNC flag. I can't see why we couldn't write > > and then sync instead, but I don't know this stuff as well as I should; > > does the following look reasonable to people? > > Bruce changed the code to implement stable writes by calling > vfs_fsync_range(). I can't see why we couldn't use O_SYNC instead. > > It seems like you are making a change just for the sake of making a change. > Is there some reason that you think a separate 'sync' is more efficient than > using O_SYNC ? Oh, sorry, see the changelog on the second patch: the problem is that the struct file can be shared across multiple writes in the NFSv4 case, so a single stable write could make all subsequent writes synchronous. (And some day people would like filehandle caching for v2/v3, in which case we'll run into the same problem.) > As a general principle, I think it is best to give the file system as much > information as possible to that it can make whatever optimisation decisions > that it wants to. > > Setting O_SYNC gives the filesystem more information than not, because it > allows it to change the behaviour of the 'write' request... though I don't > know if any filesystem actually uses the information. I'm not sure how to figure out if that's a real problem or not. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
