When using the I/O accessors in raw mode from the boot stubs we don't
want to bother with any of the complexity associated with readl/writel
and friends. Furthermore, utilization within the context of the host
driver itself is all performed on an ioremapped window, so using the
__raw variants there doesn't pose any problem either.

If and when barriers need to be added in the future, these will need to
be explicitly written out, but this is so far not a concern for any of
the affected CPUs in question.

This fixes up the link error introduced by the ARM tree via its barrier
refactoring:

	arch/arm/boot/compressed/mmcif-sh7372.o: In function `mmcif_loader':
	mmcif-sh7372.c:(.text+0x9e8): undefined reference to `outer_cache

Following the change in:

	http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=6275/1Reported-by: NSimon Horman <horms@verge.net.au>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

In the current implementation mem_cgroup_end_migration() decides whether
the page migration has succeeded or not by checking "oldpage->mapping".

But if we are tring to migrate a shmem swapcache, the page->mapping of it
is NULL from the begining, so the check would be invalid.  As a result,
mem_cgroup_end_migration() assumes the migration has succeeded even if
it's not, so "newpage" would be freed while it's not uncharged.

This patch fixes it by passing mem_cgroup_end_migration() the result of
the page migration.
Signed-off-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Acked-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce a new bit spin lock, PCG_MOVE_LOCK, to synchronize the page
accounting and migration code.  This reworks the locking scheme of
_update_stat() and _move_account() by adding new lock bit PCG_MOVE_LOCK,
which is always taken under IRQ disable.

1. If pages are being migrated from a memcg, then updates to that
   memcg page statistics are protected by grabbing PCG_MOVE_LOCK using
   move_lock_page_cgroup().  In an upcoming commit, memcg dirty page
   accounting will be updating memcg page accounting (specifically: num
   writeback pages) from IRQ context (softirq).  Avoid a deadlocking
   nested spin lock attempt by disabling irq on the local processor when
   grabbing the PCG_MOVE_LOCK.

2. lock for update_page_stat is used only for avoiding race with
   move_account().  So, IRQ awareness of lock_page_cgroup() itself is not
   a problem.  The problem is between mem_cgroup_update_page_stat() and
   mem_cgroup_move_account_page().

Trade-off:
  * Changing lock_page_cgroup() to always disable IRQ (or
    local_bh) has some impacts on performance and I think
    it's bad to disable IRQ when it's not necessary.
  * adding a new lock makes move_account() slower.  Score is
    here.

Performance Impact: moving a 8G anon process.

Before:
	real    0m0.792s
	user    0m0.000s
	sys     0m0.780s

After:
	real    0m0.854s
	user    0m0.000s
	sys     0m0.842s

This score is bad but planned patches for optimization can reduce
this impact.
Signed-off-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NGreg Thelen <gthelen@google.com>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Acked-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrea Righi <arighi@develer.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Replace usage of the mem_cgroup_update_file_mapped() memcg
statistic update routine with two new routines:
* mem_cgroup_inc_page_stat()
* mem_cgroup_dec_page_stat()

As before, only the file_mapped statistic is managed.  However, these more
general interfaces allow for new statistics to be more easily added.  New
statistics are added with memcg dirty page accounting.
Signed-off-by: NGreg Thelen <gthelen@google.com>
Signed-off-by: NAndrea Righi <arighi@develer.com>
Acked-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patchset provides the ability for each cgroup to have independent
dirty page limits.

Limiting dirty memory is like fixing the max amount of dirty (hard to
reclaim) page cache used by a cgroup.  So, in case of multiple cgroup
writers, they will not be able to consume more than their designated share
of dirty pages and will be forced to perform write-out if they cross that
limit.

The patches are based on a series proposed by Andrea Righi in Mar 2010.

Overview:

- Add page_cgroup flags to record when pages are dirty, in writeback, or nfs
  unstable.

- Extend mem_cgroup to record the total number of pages in each of the
  interesting dirty states (dirty, writeback, unstable_nfs).

- Add dirty parameters similar to the system-wide  /proc/sys/vm/dirty_*
  limits to mem_cgroup.  The mem_cgroup dirty parameters are accessible
  via cgroupfs control files.

- Consider both system and per-memcg dirty limits in page writeback when
  deciding to queue background writeback or block for foreground writeback.

Known shortcomings:

- When a cgroup dirty limit is exceeded, then bdi writeback is employed to
  writeback dirty inodes.  Bdi writeback considers inodes from any cgroup, not
  just inodes contributing dirty pages to the cgroup exceeding its limit.

- When memory.use_hierarchy is set, then dirty limits are disabled.  This is a
  implementation detail.  An enhanced implementation is needed to check the
  chain of parents to ensure that no dirty limit is exceeded.

Performance data:
- A page fault microbenchmark workload was used to measure performance, which
  can be called in read or write mode:
        f = open(foo. $cpu)
        truncate(f, 4096)
        alarm(60)
        while (1) {
                p = mmap(f, 4096)
                if (write)
			*p = 1
		else
			x = *p
                munmap(p)
        }

- The workload was called for several points in the patch series in different
  modes:
  - s_read is a single threaded reader
  - s_write is a single threaded writer
  - p_read is a 16 thread reader, each operating on a different file
  - p_write is a 16 thread writer, each operating on a different file

- Measurements were collected on a 16 core non-numa system using "perf stat
  --repeat 3".  The -a option was used for parallel (p_*) runs.

- All numbers are page fault rate (M/sec).  Higher is better.

- To compare the performance of a kernel without non-memcg compare the first and
  last rows, neither has memcg configured.  The first row does not include any
  of these memcg patches.

- To compare the performance of using memcg dirty limits, compare the baseline
  (2nd row titled "w/ memcg") with the the code and memcg enabled (2nd to last
  row titled "all patches").

                           root_cgroup                    child_cgroup
                 s_read s_write p_read p_write   s_read s_write p_read p_write
mmotm w/o memcg   0.428  0.390   0.429  0.388
mmotm w/ memcg    0.411  0.378   0.391  0.362     0.412  0.377   0.385  0.363
all patches       0.384  0.360   0.370  0.348     0.381  0.363   0.368  0.347
all patches       0.431  0.402   0.427  0.395
  w/o memcg

This patch:

Add additional flags to page_cgroup to track dirty pages within a
mem_cgroup.
Signed-off-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NAndrea Righi <arighi@develer.com>
Signed-off-by: NGreg Thelen <gthelen@google.com>
Acked-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

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>

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>

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>

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>

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>

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 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>

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>

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>

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>

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>

Add madvise MADV_HUGEPAGE to mark regions that are 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>
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>

Lately I've been working to make KVM use hugepages transparently without
the usual restrictions of hugetlbfs.  Some of the restrictions I'd like to
see removed:

1) hugepages have to be swappable or the guest physical memory remains
   locked in RAM and can't be paged out to swap

2) if a hugepage allocation fails, regular pages should be allocated
   instead and mixed in the same vma without any failure and without
   userland noticing

3) if some task quits and more hugepages become available in the
   buddy, guest physical memory backed by regular pages should be
   relocated on hugepages automatically in regions under
   madvise(MADV_HUGEPAGE) (ideally event driven by waking up the
   kernel deamon if the order=HPAGE_PMD_SHIFT-PAGE_SHIFT list becomes
   not null)

4) avoidance of reservation and maximization of use of hugepages whenever
   possible. Reservation (needed to avoid runtime fatal faliures) may be ok for
   1 machine with 1 database with 1 database cache with 1 database cache size
   known at boot time. It's definitely not feasible with a virtualization
   hypervisor usage like RHEV-H that runs an unknown number of virtual machines
   with an unknown size of each virtual machine with an unknown amount of
   pagecache that could be potentially useful in the host for guest not using
   O_DIRECT (aka cache=off).

hugepages in the virtualization hypervisor (and also in the guest!) are
much more important than in a regular host not using virtualization,
becasue with NPT/EPT they decrease the tlb-miss cacheline accesses from 24
to 19 in case only the hypervisor uses transparent hugepages, and they
decrease the tlb-miss cacheline accesses from 19 to 15 in case both the
linux hypervisor and the linux guest both uses this patch (though the
guest will limit the addition speedup to anonymous regions only for
now...).  Even more important is that the tlb miss handler is much slower
on a NPT/EPT guest than for a regular shadow paging or no-virtualization
scenario.  So maximizing the amount of virtual memory cached by the TLB
pays off significantly more with NPT/EPT than without (even if there would
be no significant speedup in the tlb-miss runtime).

The first (and more tedious) part of this work requires allowing the VM to
handle anonymous hugepages mixed with regular pages transparently on
regular anonymous vmas.  This is what this patch tries to achieve in the
least intrusive possible way.  We want hugepages and hugetlb to be used in
a way so that all applications can benefit without changes (as usual we
leverage the KVM virtualization design: by improving the Linux VM at
large, KVM gets the performance boost too).

The most important design choice is: always fallback to 4k allocation if
the hugepage allocation fails!  This is the _very_ opposite of some large
pagecache patches that failed with -EIO back then if a 64k (or similar)
allocation failed...

Second important decision (to reduce the impact of the feature on the
existing pagetable handling code) is that at any time we can split an
hugepage into 512 regular pages and it has to be done with an operation
that can't fail.  This way the reliability of the swapping isn't decreased
(no need to allocate memory when we are short on memory to swap) and it's
trivial to plug a split_huge_page* one-liner where needed without
polluting the VM.  Over time we can teach mprotect, mremap and friends to
handle pmd_trans_huge natively without calling split_huge_page*.  The fact
it can't fail isn't just for swap: if split_huge_page would return -ENOMEM
(instead of the current void) we'd need to rollback the mprotect from the
middle of it (ideally including undoing the split_vma) which would be a
big change and in the very wrong direction (it'd likely be simpler not to
call split_huge_page at all and to teach mprotect and friends to handle
hugepages instead of rolling them back from the middle).  In short the
very value of split_huge_page is that it can't fail.

The collapsing and madvise(MADV_HUGEPAGE) part will remain separated and
incremental and it'll just be an "harmless" addition later if this initial
part is agreed upon.  It also should be noted that locking-wise replacing
regular pages with hugepages is going to be very easy if compared to what
I'm doing below in split_huge_page, as it will only happen when
page_count(page) matches page_mapcount(page) if we can take the PG_lock
and mmap_sem in write mode.  collapse_huge_page will be a "best effort"
that (unlike split_huge_page) can fail at the minimal sign of trouble and
we can try again later.  collapse_huge_page will be similar to how KSM
works and the madvise(MADV_HUGEPAGE) will work similar to
madvise(MADV_MERGEABLE).

The default I like is that transparent hugepages are used at page fault
time.  This can be changed with
/sys/kernel/mm/transparent_hugepage/enabled.  The control knob can be set
to three values "always", "madvise", "never" which mean respectively that
hugepages are always used, or only inside madvise(MADV_HUGEPAGE) regions,
or never used.  /sys/kernel/mm/transparent_hugepage/defrag instead
controls if the hugepage allocation should defrag memory aggressively
"always", only inside "madvise" regions, or "never".

The pmd_trans_splitting/pmd_trans_huge locking is very solid.  The
put_page (from get_user_page users that can't use mmu notifier like
O_DIRECT) that runs against a __split_huge_page_refcount instead was a
pain to serialize in a way that would result always in a coherent page
count for both tail and head.  I think my locking solution with a
compound_lock taken only after the page_first is valid and is still a
PageHead should be safe but it surely needs review from SMP race point of
view.  In short there is no current existing way to serialize the O_DIRECT
final put_page against split_huge_page_refcount so I had to invent a new
one (O_DIRECT loses knowledge on the mapping status by the time gup_fast
returns so...).  And I didn't want to impact all gup/gup_fast users for
now, maybe if we change the gup interface substantially we can avoid this
locking, I admit I didn't think too much about it because changing the gup
unpinning interface would be invasive.

If we ignored O_DIRECT we could stick to the existing compound refcounting
code, by simply adding a get_user_pages_fast_flags(foll_flags) where KVM
(and any other mmu notifier user) would call it without FOLL_GET (and if
FOLL_GET isn't set we'd just BUG_ON if nobody registered itself in the
current task mmu notifier list yet).  But O_DIRECT is fundamental for
decent performance of virtualized I/O on fast storage so we can't avoid it
to solve the race of put_page against split_huge_page_refcount to achieve
a complete hugepage feature for KVM.

Swap and oom works fine (well just like with regular pages ;).  MMU
notifier is handled transparently too, with the exception of the young bit
on the pmd, that didn't have a range check but I think KVM will be fine
because the whole point of hugepages is that EPT/NPT will also use a huge
pmd when they notice gup returns pages with PageCompound set, so they
won't care of a range and there's just the pmd young bit to check in that
case.

NOTE: in some cases if the L2 cache is small, this may slowdown and waste
memory during COWs because 4M of memory are accessed in a single fault
instead of 8k (the payoff is that after COW the program can run faster).
So we might want to switch the copy_huge_page (and clear_huge_page too) to
not temporal stores.  I also extensively researched ways to avoid this
cache trashing with a full prefault logic that would cow in 8k/16k/32k/64k
up to 1M (I can send those patches that fully implemented prefault) but I
concluded they're not worth it and they add an huge additional complexity
and they remove all tlb benefits until the full hugepage has been faulted
in, to save a little bit of memory and some cache during app startup, but
they still don't improve substantially the cache-trashing during startup
if the prefault happens in >4k chunks.  One reason is that those 4k pte
entries copied are still mapped on a perfectly cache-colored hugepage, so
the trashing is the worst one can generate in those copies (cow of 4k page
copies aren't so well colored so they trashes less, but again this results
in software running faster after the page fault).  Those prefault patches
allowed things like a pte where post-cow pages were local 4k regular anon
pages and the not-yet-cowed pte entries were pointing in the middle of
some hugepage mapped read-only.  If it doesn't payoff substantially with
todays hardware it will payoff even less in the future with larger l2
caches, and the prefault logic would blot the VM a lot.  If one is
emebdded transparent_hugepage can be disabled during boot with sysfs or
with the boot commandline parameter transparent_hugepage=0 (or
transparent_hugepage=2 to restrict hugepages inside madvise regions) that
will ensure not a single hugepage is allocated at boot time.  It is simple
enough to just disable transparent hugepage globally and let transparent
hugepages be allocated selectively by applications in the MADV_HUGEPAGE
region (both at page fault time, and if enabled with the
collapse_huge_page too through the kernel daemon).

This patch supports only hugepages mapped in the pmd, archs that have
smaller hugepages will not fit in this patch alone.  Also some archs like
power have certain tlb limits that prevents mixing different page size in
the same regions so they will not fit in this framework that requires
"graceful fallback" to basic PAGE_SIZE in case of physical memory
fragmentation.  hugetlbfs remains a perfect fit for those because its
software limits happen to match the hardware limits.  hugetlbfs also
remains a perfect fit for hugepage sizes like 1GByte that cannot be hoped
to be found not fragmented after a certain system uptime and that would be
very expensive to defragment with relocation, so requiring reservation.
hugetlbfs is the "reservation way", the point of transparent hugepages is
not to have any reservation at all and maximizing the use of cache and
hugepages at all times automatically.

Some performance result:

vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largep
ages3
memset page fault 1566023
memset tlb miss 453854
memset second tlb miss 453321
random access tlb miss 41635
random access second tlb miss 41658
vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largepages3
memset page fault 1566471
memset tlb miss 453375
memset second tlb miss 453320
random access tlb miss 41636
random access second tlb miss 41637
vmx andrea # ./largepages3
memset page fault 1566642
memset tlb miss 453417
memset second tlb miss 453313
random access tlb miss 41630
random access second tlb miss 41647
vmx andrea # ./largepages3
memset page fault 1566872
memset tlb miss 453418
memset second tlb miss 453315
random access tlb miss 41618
random access second tlb miss 41659
vmx andrea # echo 0 > /proc/sys/vm/transparent_hugepage
vmx andrea # ./largepages3
memset page fault 2182476
memset tlb miss 460305
memset second tlb miss 460179
random access tlb miss 44483
random access second tlb miss 44186
vmx andrea # ./largepages3
memset page fault 2182791
memset tlb miss 460742
memset second tlb miss 459962
random access tlb miss 43981
random access second tlb miss 43988

============
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>

#define SIZE (3UL*1024*1024*1024)

int main()
{
	char *p = malloc(SIZE), *p2;
	struct timeval before, after;

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset page fault %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset second tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	for (p2 = p; p2 < p+SIZE; p2 += 4096)
		*p2 = 0;
	gettimeofday(&after, NULL);
	printf("random access tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	for (p2 = p; p2 < p+SIZE; p2 += 4096)
		*p2 = 0;
	gettimeofday(&after, NULL);
	printf("random access second tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	return 0;
}
============
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Transparent hugepage allocations must be allowed not to invoke kswapd or
any other kind of indirect reclaim (especially when the defrag sysfs is
control disabled).  It's unacceptable to swap out anonymous pages
(potentially anonymous transparent hugepages) in order to create new
transparent hugepages.  This is true for the MADV_HUGEPAGE areas too
(swapping out a kvm virtual machine and so having it suffer an unbearable
slowdown, so another one with guest physical memory marked MADV_HUGEPAGE
can run 30% faster if it is running memory intensive workloads, makes no
sense).  If a transparent hugepage allocation fails the slowdown is minor
and there is total fallback, so kswapd should never be asked to swapout
memory to allow the high order allocation to succeed.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

This should work for both hugetlbfs and transparent hugepages.

[akpm@linux-foundation.org: bring forward PageTransCompound() addition for bisectability]
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Move the copy/clear_huge_page functions to common code to share between
hugetlb.c and huge_memory.c.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

This increase the size of the mm struct a bit but it is needed to
preallocate one pte for each hugepage so that split_huge_page will not
require a fail path.  Guarantee of success is a fundamental property of
split_huge_page to avoid decrasing swapping reliability and to avoid
adding -ENOMEM fail paths that would otherwise force the hugepage-unaware
VM code to learn rolling back in the middle of its pte mangling operations
(if something we need it to learn handling pmd_trans_huge natively rather
being capable of rollback).  When split_huge_page runs a pte is needed to
succeed the split, to map the newly splitted regular pages with a regular
pte.  This way all existing VM code remains backwards compatible by just
adding a split_huge_page* one liner.  The memory waste of those
preallocated ptes is negligible and so it is worth it.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

split_huge_page must transform a compound page to a regular page and needs
ClearPageCompound.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Reviewed-by: NChristoph Lameter <cl@linux-foundation.org>
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>

Add mmu notifier helpers to handle pmd huge operations.
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>

pte alloc routines must wait for split_huge_page if the pmd is not present
and not null (i.e.  pmd_trans_splitting).  The additional branches are
optimized away at compile time by pmd_trans_splitting if the config option
is off.  However we must pass the vma down in order to know the anon_vma
lock to wait for.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

Some are needed to build but not actually used on archs not supporting
transparent hugepages.  Others like pmdp_clear_flush are used by x86 too.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

These returns 0 at compile time when the config option is disabled, to
allow gcc to eliminate the transparent hugepage function calls at compile
time without additional #ifdefs (only the export of those functions have
to be visible to gcc but they won't be required at link time and
huge_memory.o can be not built at all).

_PAGE_BIT_UNUSED1 is never used for pmd, only on pte.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

huge_memory.c needs it too when it fallbacks in copying hugepages into
regular fragmented pages if hugepage allocation fails during COW.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

Alter compound get_page/put_page to keep references on subpages too, in
order to allow __split_huge_page_refcount to split an hugepage even while
subpages have been pinned by one of the get_user_pages() variants.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-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>

Add a new compound_lock() needed to serialize put_page against
__split_huge_page_refcount().
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>

Define MADV_HUGEPAGE.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
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>

Simon Kirby reported the following problem

   We're seeing cases on a number of servers where cache never fully
   grows to use all available memory.  Sometimes we see servers with 4 GB
   of memory that never seem to have less than 1.5 GB free, even with a
   constantly-active VM.  In some cases, these servers also swap out while
   this happens, even though they are constantly reading the working set
   into memory.  We have been seeing this happening for a long time; I
   don't think it's anything recent, and it still happens on 2.6.36.

After some debugging work by Simon, Dave Hansen and others, the prevaling
theory became that kswapd is reclaiming order-3 pages requested by SLUB
too aggressive about it.

There are two apparent problems here.  On the target machine, there is a
small Normal zone in comparison to DMA32.  As kswapd tries to balance all
zones, it would continually try reclaiming for Normal even though DMA32
was balanced enough for callers.  The second problem is that
sleeping_prematurely() does not use the same logic as balance_pgdat() when
deciding whether to sleep or not.  This keeps kswapd artifically awake.

A number of tests were run and the figures from previous postings will
look very different for a few reasons.  One, the old figures were forcing
my network card to use GFP_ATOMIC in attempt to replicate Simon's problem.
 Second, I previous specified slub_min_order=3 again in an attempt to
reproduce Simon's problem.  In this posting, I'm depending on Simon to say
whether his problem is fixed or not and these figures are to show the
impact to the ordinary cases.  Finally, the "vmscan" figures are taken
from /proc/vmstat instead of the tracepoints.  There is less information
but recording is less disruptive.

The first test of relevance was postmark with a process running in the
background reading a large amount of anonymous memory in blocks.  The
objective was to vaguely simulate what was happening on Simon's machine
and it's memory intensive enough to have kswapd awake.

POSTMARK
                                            traceonly          kanyzone
Transactions per second:              156.00 ( 0.00%)   153.00 (-1.96%)
Data megabytes read per second:        21.51 ( 0.00%)    21.52 ( 0.05%)
Data megabytes written per second:     29.28 ( 0.00%)    29.11 (-0.58%)
Files created alone per second:       250.00 ( 0.00%)   416.00 (39.90%)
Files create/transact per second:      79.00 ( 0.00%)    76.00 (-3.95%)
Files deleted alone per second:       520.00 ( 0.00%)   420.00 (-23.81%)
Files delete/transact per second:      79.00 ( 0.00%)    76.00 (-3.95%)

MMTests Statistics: duration
User/Sys Time Running Test (seconds)         16.58      17.4
Total Elapsed Time (seconds)                218.48    222.47

VMstat Reclaim Statistics: vmscan
Direct reclaims                                  0          4
Direct reclaim pages scanned                     0        203
Direct reclaim pages reclaimed                   0        184
Kswapd pages scanned                        326631     322018
Kswapd pages reclaimed                      312632     309784
Kswapd low wmark quickly                         1          4
Kswapd high wmark quickly                      122        475
Kswapd skip congestion_wait                      1          0
Pages activated                             700040     705317
Pages deactivated                           212113     203922
Pages written                                 9875       6363

Total pages scanned                         326631    322221
Total pages reclaimed                       312632    309968
%age total pages scanned/reclaimed          95.71%    96.20%
%age total pages scanned/written             3.02%     1.97%

proc vmstat: Faults
Major Faults                                   300       254
Minor Faults                                645183    660284
Page ins                                    493588    486704
Page outs                                  4960088   4986704
Swap ins                                      1230       661
Swap outs                                     9869      6355

Performance is mildly affected because kswapd is no longer doing as much
work and the background memory consumer process is getting in the way.
Note that kswapd scanned and reclaimed fewer pages as it's less aggressive
and overall fewer pages were scanned and reclaimed.  Swap in/out is
particularly reduced again reflecting kswapd throwing out fewer pages.

The slight performance impact is unfortunate here but it looks like a
direct result of kswapd being less aggressive.  As the bug report is about
too many pages being freed by kswapd, it may have to be accepted for now.

The second test is a streaming IO benchmark that was previously used by
Johannes to show regressions in page reclaim.

MICRO
					 traceonly  kanyzone
User/Sys Time Running Test (seconds)         29.29     28.87
Total Elapsed Time (seconds)                492.18    488.79

VMstat Reclaim Statistics: vmscan
Direct reclaims                               2128       1460
Direct reclaim pages scanned               2284822    1496067
Direct reclaim pages reclaimed              148919     110937
Kswapd pages scanned                      15450014   16202876
Kswapd pages reclaimed                     8503697    8537897
Kswapd low wmark quickly                      3100       3397
Kswapd high wmark quickly                     1860       7243
Kswapd skip congestion_wait                    708        801
Pages activated                               9635       9573
Pages deactivated                             1432       1271
Pages written                                  223       1130

Total pages scanned                       17734836  17698943
Total pages reclaimed                      8652616   8648834
%age total pages scanned/reclaimed          48.79%    48.87%
%age total pages scanned/written             0.00%     0.01%

proc vmstat: Faults
Major Faults                                   165       221
Minor Faults                               9655785   9656506
Page ins                                      3880      7228
Page outs                                 37692940  37480076
Swap ins                                         0        69
Swap outs                                       19        15

Again fewer pages are scanned and reclaimed as expected and this time the
test completed faster.  Note that kswapd is hitting its watermarks faster
(low and high wmark quickly) which I expect is due to kswapd reclaiming
fewer pages.

I also ran fs-mark, iozone and sysbench but there is nothing interesting
to report in the figures.  Performance is not significantly changed and
the reclaim statistics look reasonable.

Tgis patch:

When the allocator enters its slow path, kswapd is woken up to balance the
node.  It continues working until all zones within the node are balanced.
For order-0 allocations, this makes perfect sense but for higher orders it
can have unintended side-effects.  If the zone sizes are imbalanced,
kswapd may reclaim heavily within a smaller zone discarding an excessive
number of pages.  The user-visible behaviour is that kswapd is awake and
reclaiming even though plenty of pages are free from a suitable zone.

This patch alters the "balance" logic for high-order reclaim allowing
kswapd to stop if any suitable zone becomes balanced to reduce the number
of pages it reclaims from other zones.  kswapd still tries to ensure that
order-0 watermarks for all zones are met before sleeping.
Signed-off-by: NMel Gorman <mel@csn.ul.ie>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: NEric B Munson <emunson@mgebm.net>
Cc: Simon Kirby <sim@hostway.ca>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

page_mapping() has a unlikely that the mapping has PAGE_MAPPING_ANON set.
But running the annotated branch profiler on a normal desktop system doing
vairous tasks (xchat, evolution, firefox, distcc), it is not really that
unlikely that the mapping here will have the PAGE_MAPPING_ANON flag set:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
35935762 1270265395  97 page_mapping                   mm.h                 659
1306198001   143659   0 page_mapping                   mm.h                 657
203131478   121586   0 page_mapping                   mm.h                 657
 5415491     1116   0 page_mapping                   mm.h                 657
74899487     1116   0 page_mapping                   mm.h                 657
203132845      224   0 page_mapping                   mm.h                 659
 5415464       27   0 page_mapping                   mm.h                 659
   13552        0   0 page_mapping                   mm.h                 657
   13552        0   0 page_mapping                   mm.h                 659
  242630        0   0 page_mapping                   mm.h                 657
  242630        0   0 page_mapping                   mm.h                 659
74899487        0   0 page_mapping                   mm.h                 659

The page_mapping() is a static inline, which is why it shows up multiple
times.

The unlikely in page_mapping() was correct a total of 1909540379 times and
incorrect 1270533123 times, with a 39% being incorrect.  With this much of
an error, it's best to simply remove the unlikely and have the compiler
and branch prediction figure this out.
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>