2011/6/11 Hugh Dickins [off-list ref]:

On Fri, 10 Jun 2011, KAMEZAWA Hiroyuki wrote:

quoted

I think this can be a fix.

Sorry, I think not: I've not digested your rationale,
but three things stand out:

1. Why has this only just started happening?  I may not have run that
  test on 3.0-rc1, but surely I ran it for hours with 2.6.39;
  maybe not with khugepaged, but certainly with ksmd.

Not sure. I pointed this just by review because I found "charge" in
khugepaged is out of mmap_sem now.

2. Your hunk below:

quoted

-     if (!mm_need_new_owner(mm, p))
+     if (!mm_need_new_owner(mm, p)) {
+             rcu_assign_pointer(mm->owner, NULL);

  is now setting mm->owner to NULL at times when we were sure it did not
  need updating before (task is not the owner): you're damaging mm->owner.

Ah, yes. It's my mistake.

3. There's a patch from Andrea in 3.0-rc1 which looks very likely to be
  relevant, 692e0b35427a "mm: thp: optimize memcg charge in khugepaged".
  I'll try reproducing without that tonight (I crashed in 20 minutes
  this morning, so it's not too hard).

Thanks,
-Kame

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