On Tue, 30 Oct 2012 10:07:25 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: > 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.) Ahh, I missed that. Makes sense then, thanks. > > > 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. Search all filesystems for special handling of O_SYNC or O_DSYNC? I strongly suspect that it is not a real problem. Thanks, NeilBrown
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