Re: [RFC PATCH 0/4]: affinity-on-next-touch

[Stefan Lankes]

Lee Schermerhorn wrote:
> On Thu, 2009-06-18 at 15:04 -0400, Lee Schermerhorn wrote:
> > On Thu, 2009-06-18 at 00:37 -0400, Lee Schermerhorn wrote:
> > > On Wed, 2009-06-17 at 09:45 +0200, Stefan Lankes wrote:
> > > > > I've placed the last rebased version in :
> > > > >
> > > > > http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.28-rc4-mmotm-
> > > > > 081110/
> > > > OK! I will try to reconstruct the problem.
> > > Stefan:
> > >
> > > Today I rebased the migrate on fault patches to 2.6.30-mmotm-090612...
> > > [along with my shared policy series atop which they sit in my tree].
> > > Patches reside in:
> > >
> > > http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.30-mmotm-090612-1220/
> > I have updated the migrate-on-fault tarball in the above location to fix
> > part of the problems I was seeing.  See below.
> >
> > > I did a quick test.  I'm afraid the patches have suffered some "bit rot"
> > > vis a vis mainline/mmotm over the past several months.  Two possibly
> > > related issues:
> > >
> > > 1) lazy migration doesn't seem to work. Looks like
> > > mbind(<some-policy>+MPOL_MF_MOVE+MPOL_MF_LAZY) is not unmapping the
> > > pages so, of course, migrate on fault won't work.  I suspect the
> > > reference count handling has changed since I last tried this.  [Note one
> > > of the patch conflicts was in the MPOL_MF_LAZY addition to the mbind
> > > flag definitions in mempolicy.h and I may have botched the resolution
> > > thereof.]
> > >
> > > 2) When the pages get freed on exit/unmap, they are still PageLocked()
> > > and free_pages_check()/bad_page() bugs out with bad page state.
> > >
> > > Note:  This is independent of memcg--i.e., happens whether or not memcg
> > > configured.
> > <snip>
> >
> > OK.  Found time to look at this.  Turns out I hadn't tested since
> > trylock_page() was introduced.  I did a one-for-one replacement of the
> > old API [TestSetPageLocked()], not noticing that the sense of the return
> > was inverted.  Thus, I was bailing out of the migrate_pages_unmap_only()
> > loop with the page locked, thinking someone else had locked it and would
> > take care of it.  Since the page wasn't unmapped from the page table[s],
> > of course it wouldn't migrate on fault--wouldn't even fault!
> >
> > Fixed this.
> >
> > Now:  lazy migration works w/ or w/o memcg configured, but NOT with the
> > swap resource controller configured.  I'll look at that as time permits.
>
> Update:  I now can't reproduce the lazy migration failure with the swap
> resource controller configured.  Perhaps I had booted the wrong kernel
> for the test reported above.  Now the updated patch series mentioned
> above seems to be working with both memory and swap resource controllers
> configured for simple memtoy driven lazy migration.

The current version of your patch works fine on my system. I tested the 
patches with our test applications and got very good performance results!

Stefan
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