Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 

On Fri, Jun 01 2007, Neil Brown wrote:
> On Friday June 1, [email protected] wrote:
> > On Thu, May 31, 2007 at 02:31:21PM -0400, Phillip Susi wrote:
> > > David Chinner wrote:
> > > >That sounds like a good idea - we can leave the existing
> > > >WRITE_BARRIER behaviour unchanged and introduce a new WRITE_ORDERED
> > > >behaviour that only guarantees ordering. The filesystem can then
> > > >choose which to use where appropriate....
> > > 
> > > So what if you want a synchronous write, but DON'T care about the order? 
> > 
> > submit_bio(WRITE_SYNC, bio);
> > 
> > Already there, already used by XFS, JFS and direct I/O.
> 
> Are you sure?
> 
> You seem to be saying that WRITE_SYNC causes the write to be safe on
> media before the request returns.  That isn't my understanding.
> I think (from comments near the definition and a quick grep through
> the code) that WRITE_SYNC expedites the delivery of the request
> through the elevator, but doesn't do anything special about getting it
> onto the media.
> It essentially say "Submit this request now, don't wait for more
> request to bundle with it for better bandwidth utilisation"

That is exactly right. WRITE_SYNC doesn't give any integrity guarentees,
it's just makes sure it goes straight through the io scheduler.

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux