F16 unusable while writing to pendrive [SOLVED -- not]

[Patrick O'Callaghan]

On Sat, 2012-01-21 at 14:05 -0430, Patrick O'Callaghan wrote:
> On Sat, 2011-12-17 at 21:17 -0430, Patrick O'Callaghan wrote:
> > On Sun, 2011-12-18 at 01:37 +0000, Marko Vojinovic wrote:
> > > On Saturday 17 December 2011 19:41:38 Patrick O'Callaghan wrote:
> > > > This looks like a regression. Under F15 when I wrote large files to a
> > > > pendrive, the system would become a little sluggish. Now it essentially
> > > > freezes until the write terminates. What I mean is that the UI is almost
> > > > completely unresponsive; even clicking between two terminal windows is
> > > > so slow that you can see the window contents refresh, followed several
> > > > seconds later by the frame.
> > > > 
> > > > Fully updated F16 with KDE, Intel Core 2 Dual, 4GB RAM, Intel onboard
> > > > graphics. The pendrive is an 8GB Patriot Xporter (a year or two old)
> > > > under USB-2 with no intervening hub.
> > > 
> > > Oh yes, this is one of my favourities... :-D
> > > 
> > > There's a very good article at LWN discussing precisely this issue:
> > > 
> > >    http://lwn.net/Articles/467328/
> > > 
> > > You wouldn't believe how complicated these things can get... ;-) One would 
> > > naively think "yes, the USB drive is slow, but that shouldn't stop the rest of 
> > > the system from running smoothly". However, when you put into the mix the 
> > > hugemem page allocation, memory fragmentation, contradictory points of view on 
> > > how the kernel should be optimized, etc., it seems that it is quite natural 
> > > that your typical fast 3GHz system with 4GB of RAM grinds to a complete halt 
> > > during a simple write-to-USB-drive operation... :-D
> > 
> > That might be it I guess, but I'm not totally convinced. I updated
> > F15->F16 only 5 days ago, and previous to the switchover had no problems
> > of this sort, using the latest kernel for F15. It's hard to believe the
> > kernel switch from F15 to F16 can have made such a huge difference. For
> > the record, I went from:
> > 
> >         kernel-2.6.41.1-1.fc15.x86_64
> > 
> > to:
> > 
> >         kernel-3.1.5-1.fc16.x86_64
> > 
> > But as we know, the version bump from 2 to 3 is meaningless in itself.
> 
> This was really bothering me (I make frequent use of pendrives) so took
> another look at the above article, then
> at /usr/share/doc/kernel-doc-3.1.9/Documentation/vm/transhuge.txt, where
> it explains how to turn off the Transparent Huge Pages feature. I added
> transparent_hugepage=never to my boot params, rebooted, and the problem
> appears to have been fixed.
> 
> Note: YMMV. This works for me with my workload (no long jobs or
> intensive compute load). Others may find it impacts their performance,
> but it shouldn't break anything.

I spoke too soon. The performance improvement must have been due to me
having just rebooted. In fact neither the boot param nor attempting to
write to /sys/kernel/mm/transparent_hugepage/enabled have any effect.
The latter *always* shows THP to be enabled and won't allow it to be
overwritten, even as root.

Apparently kernel 3.3 will have a fix for this problem, but that's
expected to be around the end of March unless someone backports it.

poc