Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed)

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

 



On Sun, 16 Aug 2009 15:05:30 +0100
Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:

> On Sat, 15 Aug 2009 08:55:17 -0500
> James Bottomley <James.Bottomley@xxxxxxx> wrote:
> 
> > On Sat, 2009-08-15 at 09:22 -0400, Mark Lord wrote:
> > > James Bottomley wrote:
> > > >
> > > > This means you have to drain the outstanding NCQ commands
> > > > (stalling the device) before you can send a TRIM.   If we do
> > > > this for every discard, the performance impact will be pretty
> > > > devastating, hence the need to coalesce.  It's nothing really
> > > > to do with device characteristics, it's an ATA protocol problem.
> > > ..
> > > 
> > > I don't think that's really much of an issue -- we already have
> > > to do that for cache-flushes whenever barriers are enabled.  Yes
> > > it costs, but not too much.
> > 
> > That's not really what the enterprise is saying about flush
> > barriers. True, not all the performance problems are NCQ queue
> > drain, but for a steady workload they are significant.
> 
> Flush barriers are nightmare for more than enterprise. You drive
> basically goes for a hike for a bit which trashes interactivity as
> well. If the device can't do trim and the like without a drain I
> don't see much point doing it at all, except maybe to wait for idle
> devices and run a filesystem managed background 'strimmer' thread to
> just weed out now idle blocks that have stayed idle - eg by adding an
> inode of all the deleted untrimmed blocks and giving it an irregular
> empty ?
> 

trim is mostly for ssd's though, and those tend to not have the "goes
for a hike" behavior as much......

I wonder if it's worse to batch stuff up, because then the trim itself
gets bigger and might take longer.....



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [SCSI Target Devel]     [Linux SCSI Target Infrastructure]     [Kernel Newbies]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Linux IIO]     [Samba]     [Device Mapper]
  Powered by Linux