Messages in this thread | | | Date | Sun, 17 Sep 2017 10:45:34 -0700 | From | Jerome Glisse <> | Subject | Re: [PATCH] mm/memcg: avoid page count check for zone device |
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On Fri, Sep 15, 2017 at 09:01:00AM +0200, Michal Hocko wrote: > On Thu 14-09-17 15:00:11, jglisse@redhat.com wrote: > > From: Jérôme Glisse <jglisse@redhat.com> > > > > Fix for 4.14, zone device page always have an elevated refcount > > of one and thus page count sanity check in uncharge_page() is > > inappropriate for them. > > > > Signed-off-by: Jérôme Glisse <jglisse@redhat.com> > > Reported-by: Evgeny Baskakov <ebaskakov@nvidia.com> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Johannes Weiner <hannes@cmpxchg.org> > > Cc: Michal Hocko <mhocko@kernel.org> > > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > > Acked-by: Michal Hocko <mhocko@suse.com> > > Side note. Wouldn't it be better to re-organize the check a bit? It is > true that this is VM_BUG so it is not usually compiled in but when it > preferably checks for unlikely cases first while the ref count will be > 0 in the prevailing cases. So can we have > VM_BUG_ON_PAGE(page_count(page) && !is_zone_device_page(page) && > !PageHWPoison(page), page); > > I would simply fold this nano optimization into the patch as you are > touching it already. Not sure it is worth a separate commit.
I am traveling sorry for late answer. This nano optimization make sense Andrew do you want me to respin or should we leave it be ? I don't mind either way.
Cheers, Jérôme
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