mm: migration: use rcu_dereference_protected when dereferencing the radix tree slot during file page migration

migrate_pages() -> unmap_and_move() only calls rcu_read_lock() for
anonymous pages, as introduced by git commit
989f89c5 ("fix rcu_read_lock() in page
migraton").  The point of the RCU protection there is part of getting a
stable reference to anon_vma and is only held for anon pages as file pages
are locked which is sufficient protection against freeing.

However, while a file page's mapping is being migrated, the radix tree is
double checked to ensure it is the expected page.  This uses
radix_tree_deref_slot() -> rcu_dereference() without the RCU lock held
triggering the following warning.

[  173.674290] ===================================================
[  173.676016] [ INFO: suspicious rcu_dereference_check() usage. ]
[  173.676016] ---------------------------------------------------
[  173.676016] include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection!
[  173.676016]
[  173.676016] other info that might help us debug this:
[  173.676016]
[  173.676016]
[  173.676016] rcu_scheduler_active = 1, debug_locks = 0
[  173.676016] 1 lock held by hugeadm/2899:
[  173.676016]  #0:  (&(&inode->i_data.tree_lock)->rlock){..-.-.}, at: [<c10e3d2b>] migrate_page_move_mapping+0x40/0x1ab
[  173.676016]
[  173.676016] stack backtrace:
[  173.676016] Pid: 2899, comm: hugeadm Not tainted 2.6.37-rc5-autobuild
[  173.676016] Call Trace:
[  173.676016]  [<c128cc01>] ? printk+0x14/0x1b
[  173.676016]  [<c1063502>] lockdep_rcu_dereference+0x7d/0x86
[  173.676016]  [<c10e3db5>] migrate_page_move_mapping+0xca/0x1ab
[  173.676016]  [<c10e41ad>] migrate_page+0x23/0x39
[  173.676016]  [<c10e491b>] buffer_migrate_page+0x22/0x107
[  173.676016]  [<c10e48f9>] ? buffer_migrate_page+0x0/0x107
[  173.676016]  [<c10e425d>] move_to_new_page+0x9a/0x1ae
[  173.676016]  [<c10e47e6>] migrate_pages+0x1e7/0x2fa

This patch introduces radix_tree_deref_slot_protected() which calls
rcu_dereference_protected().  Users of it must pass in the
mapping->tree_lock that is protecting this dereference.  Holding the tree
lock protects against parallel updaters of the radix tree meaning that
rcu_dereference_protected is allowable.

[akpm@linux-foundation.org: remove unneeded casts]
Signed-off-by: NMel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Milton Miller <miltonm@bga.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: <stable@kernel.org>		[2.6.37.early]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Cleanup some code with common compound_trans_head helper.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This makes KSM full operational with THP pages.  Subpages are scanned
while the hugepage is still in place and delivering max cpu performance,
and only if there's a match and we're going to deduplicate memory, the
single hugepages with the subpage match is split.

There will be no false sharing between ksmd and khugepaged.  khugepaged
won't collapse 2m virtual regions with KSM pages inside.  ksmd also should
only split pages when the checksum matches and we're likely to split an
hugepage for some long living ksm page (usual ksm heuristic to avoid
sharing pages that get de-cowed).
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

MADV_HUGEPAGE and MADV_NOHUGEPAGE were fully effective only if run after
mmap and before touching the memory.  While this is enough for most
usages, it's little effort to make madvise more dynamic at runtime on an
existing mapping by making khugepaged aware about madvise.

MADV_HUGEPAGE: register in khugepaged immediately without waiting a page
fault (that may not ever happen if all pages are already mapped and the
"enabled" knob was set to madvise during the initial page faults).

MADV_NOHUGEPAGE: skip vmas marked VM_NOHUGEPAGE in khugepaged to stop
collapsing pages where not needed.

[akpm@linux-foundation.org: tweak comment]
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add madvise MADV_NOHUGEPAGE to mark regions that are not important to be
hugepage backed.  Return -EINVAL if the vma is not of an anonymous type,
or the feature isn't built into the kernel.  Never silently return
success.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Define MADV_NOHUGEPAGE.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Read compound_trans_order safe. Noop for CONFIG_TRANSPARENT_HUGEPAGE=n.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

hugetlbfs was changed to allow memory failure to migrate the hugetlbfs
pages and that broke THP as split_huge_page was then called on hugetlbfs
pages too.

compound_head/order was also run unsafe on THP pages that can be splitted
at any time.

All compound_head() invocations in memory-failure.c that are run on pages
that aren't pinned and that can be freed and reused from under us (while
compound_head is running) are buggy because compound_head can return a
dangling pointer, but I'm not fixing this as this is a generic
memory-failure bug not specific to THP but it applies to hugetlbfs too, so
I can fix it later after THP is merged upstream.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add debug checks for invariants that if broken could lead to mapcount vs
page_mapcount debug checks to trigger later in split_huge_page.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add hugepage statistics to per-node sysfs meminfo
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Make sure we scale up nr_rotated when we encounter a referenced
transparent huge page.  This ensures pageout scanning balance is not
distorted when there are huge pages on the LRU.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Count each transparent hugepage as HPAGE_PMD_NR pages in the LRU
statistics, so the Active(anon) and Inactive(anon) statistics in
/proc/meminfo are correct.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

On small systems, the extra memory used by the anti-fragmentation memory
reserve and simply because huge pages are smaller than large pages can
easily outweigh the benefits of less TLB misses.

A less obvious concern is if run on a NUMA machine with asymmetric node
sizes and one of them is very small.  The reserve could make the node
unusable.

In case of the crashdump kernel, OOMs have been observed due to the
anti-fragmentation memory reserve taking up a large fraction of the
crashdump image.

This patch disables transparent hugepages on systems with less than 1GB of
RAM, but the hugepage subsystem is fully initialized so administrators can
enable THP through /sys if desired.
Signed-off-by: NRik van Riel <riel@redhat.com>
Acked-by: NAvi Kiviti <avi@redhat.com>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It makes no sense not to enable compaction for small order pages as we
don't want to end up with bad order 2 allocations and good and graceful
order 9 allocations.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This takes advantage of memory compaction to properly generate pages of
order > 0 if regular page reclaim fails and priority level becomes more
severe and we don't reach the proper watermarks.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It's unclear why schedule friendly kernel threads can't be taken away by
the CPU through the scheduler itself.  It's safer to stop them as they can
trigger memory allocation, if kswapd also freezes itself to avoid
generating I/O they have too.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

For GRU and EPT, we need gup-fast to set referenced bit too (this is why
it's correct to return 0 when shadow_access_mask is zero, it requires
gup-fast to set the referenced bit).  qemu-kvm access already sets the
young bit in the pte if it isn't zero-copy, if it's zero copy or a shadow
paging EPT minor fault we relay on gup-fast to signal the page is in
use...

We also need to check the young bits on the secondary pagetables for NPT
and not nested shadow mmu as the data may never get accessed again by the
primary pte.

Without this closer accuracy, we'd have to remove the heuristic that
avoids collapsing hugepages in hugepage virtual regions that have not even
a single subpage in use.

->test_young is full backwards compatible with GRU and other usages that
don't have young bits in pagetables set by the hardware and that should
nuke the secondary mmu mappings when ->clear_flush_young runs just like
EPT does.

Removing the heuristic that checks the young bit in
khugepaged/collapse_huge_page completely isn't so bad either probably but
I thought it was worth it and this makes it reliable.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Archs implementing Transparent Hugepage Support must implement a function
called has_transparent_hugepage to be sure the virtual or physical CPU
supports Transparent Hugepages.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

An huge pmd can only be mapped if the corresponding 2M virtual range is
fully contained in the vma.  At times the VM calls split_vma twice, if the
first split_vma succeeds and the second fail, the first split_vma remains
in effect and it's not rolled back.  For split_vma or vma_adjust to fail
an allocation failure is needed so it's a very unlikely event (the out of
memory killer would normally fire before any allocation failure is visible
to kernel and userland and if an out of memory condition happens it's
unlikely to happen exactly here).  Nevertheless it's safer to ensure that
no huge pmd can be left around if the vma is adjusted in a way that can't
fit hugepages anymore at the new vm_start/vm_end address.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It's not worth migrating transparent hugepages during compaction.  Those
hugepages don't create fragmentation.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

With transparent hugepage support we need compaction for the "defrag"
sysfs controls to be effective.

At the moment THP hangs the system if COMPACTION isn't selected, as
without COMPACTION lumpy reclaim wouldn't be entirely disabled.  So at the
moment it's not orthogonal.  When lumpy will be removed from the VM I can
remove the select COMPACTION in theory, but then 99% of THP users would be
still doing a mistake in disabling compaction, even if the mistake won't
return in fatal runtime but just slightly degraded performance.  So from a
theoretical standpoing forcing the below select is not needed (the
dependency isn't strict nor at compile time nor at runtime) but from a
practical standpoint it is safer.

If anybody really wants THP to run without compaction, it'd be such a
weird setup that editing the Kconfig file to allow it will be surely not a
problem.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Allow to choose between the always|madvise default for page faults and
khugepaged at config time.  madvise guarantees zero risk of higher memory
footprint for applications (applications using madvise(MADV_HUGEPAGE)
won't risk to use any more memory by backing their virtual regions with
hugepages).

Initially set the default to N and don't depend on EMBEDDED.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This tries to be more friendly to filesystem in userland, with userland
backends that allocate memory in the I/O paths and that could deadlock if
khugepaged holds the mmap_sem write mode of the userland backend while
allocating memory.  Memory allocation may wait for writeback I/O
completion from the daemon that may be blocked in the mmap_sem read mode
if a page fault happens and the daemon wasn't using mlock for the memory
required for the I/O submission and completion.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It's mostly a matter of replacing alloc_pages with alloc_pages_vma after
introducing alloc_pages_vma.  khugepaged needs special handling as the
allocation has to happen inside collapse_huge_page where the vma is known
and an error has to be returned to the outer loop to sleep
alloc_sleep_millisecs in case of failure.  But it retains the more
efficient logic of handling allocation failures in khugepaged in case of
CONFIG_NUMA=n.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

With memory compaction in, and lumpy-reclaim disabled, it seems safe
enough to defrag memory during the (synchronous) transparent hugepage page
faults (TRANSPARENT_HUGEPAGE_DEFRAG_FLAG) and not only during khugepaged
(async) hugepage allocations that was already enabled even before memory
compaction was in (TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG).
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If transparent hugepage is enabled initialize min_free_kbytes to an
optimal value by default.  This moves the hugeadm algorithm in kernel.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Natively handle huge pmds when changing page tables on behalf of
mprotect().

I left out update_mmu_cache() because we do not need it on x86 anyway but
more importantly the interface works on ptes, not pmds.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Flushing the tlb for huge pmds requires the vma's anon_vma, so pass along
the vma instead of the mm, we can always get the latter when we need it.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add pmd_modify() for use with mprotect() on huge pmds.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Handle transparent huge page pmd entries natively instead of splitting
them into subpages.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add support for transparent hugepages to x86 32bit.

Share the same VM_ bitflag for VM_MAPPED_COPY.  mm/nommu.c will never
support transparent hugepages.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

PG_buddy can be converted to _mapcount == -2.  So the PG_compound_lock can
be added to page->flags without overflowing (because of the sparse section
bits increasing) with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y.  This also
has to move the memory hotplug code from _mapcount to lru.next to avoid
any risk of clashes.  We can't use lru.next for PG_buddy removal, but
memory hotplug can use lru.next even more easily than the mapcount
instead.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Skip transhuge pages in ksm for now.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

register in khugepaged if the vma grows.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add khugepaged to relocate fragmented pages into hugepages if new
hugepages become available.  (this is indipendent of the defrag logic that
will have to make new hugepages available)

The fundamental reason why khugepaged is unavoidable, is that some memory
can be fragmented and not everything can be relocated.  So when a virtual
machine quits and releases gigabytes of hugepages, we want to use those
freely available hugepages to create huge-pmd in the other virtual
machines that may be running on fragmented memory, to maximize the CPU
efficiency at all times.  The scan is slow, it takes nearly zero cpu time,
except when it copies data (in which case it means we definitely want to
pay for that cpu time) so it seems a good tradeoff.

In addition to the hugepages being released by other process releasing
memory, we have the strong suspicion that the performance impact of
potentially defragmenting hugepages during or before each page fault could
lead to more performance inconsistency than allocating small pages at
first and having them collapsed into large pages later...  if they prove
themselfs to be long lived mappings (khugepaged scan is slow so short
lived mappings have low probability to run into khugepaged if compared to
long lived mappings).
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add hugepage stat information to /proc/vmstat and /proc/meminfo.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add memcg charge/uncharge to hugepage faults in huge_memory.c.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

By this patch, when a transparent hugepage is charged, not only the head
page but also all the tail pages are committed, IOW pc->mem_cgroup and
pc->flags of tail pages are set.

Without this patch:

- Tail pages are not linked to any memcg's LRU at splitting. This causes many
  problems, for example, the charged memcg's directory can never be rmdir'ed
  because it doesn't have enough pages to scan to make the usage decrease to 0.
- "rss" field in memory.stat would be incorrect. Moreover, usage_in_bytes in
  root cgroup is calculated by the stat not by res_counter(since 2.6.32),
  it would be incorrect too.
Signed-off-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Teach memcg to charge/uncharge compound pages.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

No pmd_trans_huge should ever materialize in migration ptes areas, because
we split the hugepage before migration ptes are instantiated.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>