Messages in this thread | | | Date | Sat, 11 Jun 2011 01:54:42 +0200 | From | Johannes Weiner <> | Subject | Re: [PATCH] [BUGFIX] update mm->owner even if no next owner. |
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On Fri, Jun 10, 2011 at 02:49:35PM -0700, Hugh Dickins wrote: > On Fri, 10 Jun 2011, KAMEZAWA Hiroyuki wrote: > > > > 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. > > 2. Your hunk below: > > - 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. > > 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).
It looks likely. This change moved the memcg charge out of the mmap_sem read section, which kept the last task of the mm from exiting:
do_exit exit_mm mmput khugepaged_exit down_write(&mm->mmap_sem); up_write(&mm->mmap_sem);
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