Re: [PATCH 6/6] vmscan: Kick flusher threads to clean pages when reclaim is encountering dirty pages

[Wu Fengguang <fengguang.wu@intel.com>]

On Sun, Aug 01, 2010 at 07:56:40PM +0800, Wu Fengguang wrote:
> > Sigh.  We have sooo many problems with writeback and latency.  Read
> > https://bugzilla.kernel.org/show_bug.cgi?id=12309 and weep.  Everyone's
> > running away from the issue and here we are adding code to solve some
> > alleged stack-overflow problem which seems to be largely a non-problem,
> > by making changes which may worsen our real problems.
> 
> I'm sweeping bug 12309. Most people reports some data writes, though
> relative few explicitly stated memory pressure is another necessary
> condition.

#14: Per von Zweigbergk
Ubuntu 2.6.27 slowdown when copying 25MB/s USB stick to 10 MB/s SSD.

KOSAKI and my patches won't fix 2.6.27, since it only do
congestion_wait() and wait_on_page_writeback() for order>3
allocations. There may be more bugs there.

#24: Per von Zweigbergk
The encryption of the SSD very significantly increases the problem.

This is expected. Data encryption roughly doubles page consumption
speed (there may be temp buffers allocated/dropped quickly), hence
vmscan pressure.

#26: Per von Zweigbergk
Disabling swap makes the terminal launch much faster while copying;
However Firefox and vim hang much more aggressively and frequently
during copying.

It's interesting to see processes behave differently. Is this
reproducible at all?

#34: Ben Gamari
There is evidence that x86-64 is a factor here.

Because x86-64 does order-1 page allocation in fork() and consumes
more memory (larger user space code/data)?

#36: Lari Temmes
Go from usable to totally unusable when switching from
a SMP kernel to a UP kernel on a single CPU laptop

He should be testing 2.6.28. I'm not aware of known bugs there.

#47: xyke
Renicing pdflush -10 had some great improvement on basic
responsiveness.

It sure helps :)

Too much (old) messages there. I'm hoping some of the still active
bug reporters to test the following patches (they are for the -mmotm
tree, need to unindent code for Linus's tree) and see if there are
any improvements.

http://lkml.org/lkml/2010/8/1/40
http://lkml.org/lkml/2010/8/1/45

Thanks,
Fengguang