On Mon, Dec 03, 2012 at 09:30:12AM +0100, Thorsten Leemhuis wrote:

quoted

quoted

John was able to reproduce the problem quickly with a kernel that 
contained the patch from your mail. For details see

[stripped: all the glory details of what likely went wrong and lead
to the problem john sees or saw]

---
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: [patch] mm: vmscan: do not keep kswapd looping forever due
 to individual uncompactable zones

When a zone meets its high watermark and is compactable in case of
higher order allocations, it contributes to the percentage of the
node's memory that is considered balanced.
[...]

FYI: I built a kernel with that patch. I've been running on my x86_64
machine at home over the weekend and everything was working fine (just
as without the patch). John gave it a quick try and in
https://bugzilla.redhat.com/show_bug.cgi?id=866988#c57 reported:

"""
I just installed
kernel-3.7.0-0.rc7.git1.2.van.main.knurd.kswap.4.fc18.i686 and ran my
usual load that triggers the problem.  OK so far.  I'll check again in
24hours, but looking good so far.
"""

w00t!

BTW, I built that kernel without the patch you mentioned in
http://thread.gmane.org/gmane.linux.kernel.mm/90911/focus=91153
("buffer_heads_over_limit can put kswapd into reclaim, but it's ignored
[...]) It looked to me like that patch was only meant for debugging. Let
me know if that was wrong. Ohh, and I didn't update to a fresher
mainline checkout yet to make sure the base for John's testing didn't
change.

Ah, yes, the ApplyPatch is commented out.

I think we want that upstream as well, but it's not critical.  It'll
reduce kswapd CPU usage marginally on highmem systems in certain
situations, but I don't think any of the 100% CPU usage problems are
fixed by it.

Not rebasing sounds reasonable to me to verify the patch.  It might be
worth testing that the final version that will be 3.8 still works for
John, however, once that is done.  Just to be sure.

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