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[PATCHv10 00/36] THP refcounting redesign

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  [PATCHv10 00/36] THP refcounting redesign "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 23/36] tile, thp: remove infrastructure for handling splitting PMDs "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 11/36] mm: temporally mark THP broken "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 12/36] thp: drop all split_huge_page()-related code "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 05/36] mm: adjust FOLL_SPLIT for new refcounting "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 20/36] powerpc, thp: remove infrastructure for handling splitting PMDs "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 31/36] thp, mm: split_huge_page(): caller need to lock page "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 18/36] arm, thp: remove infrastructure for handling splitting PMDs "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 04/36] mm, thp: adjust conditions when we can reuse the page on WP fault "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 16/36] mm, thp: remove compound_lock "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 24/36] x86, thp: remove infrastructure for handling splitting PMDs "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200
    [PATCHv10 22/36] sparc, thp: remove infrastructure for handling splitting PMDs "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-03 17:30 +0200

#1218358 — [PATCHv10 00/36] THP refcounting redesign

Hello everybody,

The THP refcounting has been rebased onto newer -mm tree with
compound_head patchset applied. This caused few conflicts.

Since page->lru in all tail pages occupied by page->compound_head, I had
to adjust the code to use storage of ->mapping and ->index in the second
tail page as list_head to link pages into deferred split queue.

The goal of patchset is to make refcounting on THP pages cheaper with
simpler semantics and allow the same THP compound page to be mapped with
PMD and PTEs. This is required to get reasonable THP-pagecache
implementation.

With the new refcounting design it's much easier to protect against
split_huge_page(): simple reference on a page will make you the deal.
It makes gup_fast() implementation simpler and doesn't require
special-case in futex code to handle tail THP pages.

It should improve THP utilization over the system since splitting THP in
one process doesn't necessary lead to splitting the page in all other
processes have the page mapped.

The patchset drastically lower complexity of get_page()/put_page()
codepaths. I encourage people look on this code before-and-after to
justify time budget on reviewing this patchset.

= Changelog =

v10:
  - rebased onto newer -mm tree with compound_head patchset applied.

v9:
  - rebased to mmotm-2015-07-15-16-46: fix conflicts with DAX and pagemap
    patchsets;
  - simplify PG_double_map handling in __split_huge_pmd_locked();
  - fix arm64 typo (Suzuki K. Poulose);
  - fix build on !THP;
  - checkpatch fixes;
  - Tested-by/Reviewed-by Aneesh Kumar K.V;

v8:
  - rebased to since-4.1;
  - fix mmap10 from LTP: make check and clear PG_double_map atomic.

v7:
  - avoid situation during split_huge_pmd() where we can temporarily drop
    page_mapcount() to zero. It can lead to races e.g. with unmap code;
  - update documentation;
  - fix NR_ANON_PAGES accounting in page_remove_rmap();
  - fix page_mapped();
  - optimize page_mapped() and page_mapcount();
  - fix PSS calculation for non-shared pages;

v6:
  - rebase to since-4.0;
  - optimize mapcount handling: significantely reduce overhead for most
    common cases.
  - split pages on migrate_pages();
  - remove infrastructure for handling splitting PMDs on all architectures;
  - fix page_mapcount() for hugetlb pages;

v5:
  - Tested-by: Sasha Levin!™
  - re-split patchset in hope to improve readability;
  - rebased on top of page flags and ->mapping sanitizing patchset;
  - uncharge compound_mapcount rather than mapcount for hugetlb pages
    during removing from rmap;
  - differentiate page_mapped() from page_mapcount() for compound pages;
  - rework deferred_split_huge_page() to use shrinker interface;
  - fix race in page_remove_rmap();
  - get rid of __get_page_tail();
  - few random bug fixes;
v4:
  - fix sizes reported in smaps;
  - defines instead of enum for RMAP_{EXCLUSIVE,COMPOUND};
  - skip THP pages on munlock_vma_pages_range(): they are never mlocked;
  - properly handle huge zero page on FOLL_SPLIT;
  - fix lock_page() slow path on tail pages;
  - account page_get_anon_vma() fail to THP_SPLIT_PAGE_FAILED;
  - fix split_huge_page() on huge page with unmapped head page;
  - fix transfering 'write' and 'young' from pmd to ptes on split_huge_pmd;
  - call page_remove_rmap() in unfreeze_page under ptl.

= Design overview =

The main reason why we can't map THP with 4k is how refcounting on THP
designed. It built around two requirements:

  - split of huge page should never fail;
  - we can't change interface of get_user_page();

To be able to split huge page at any point we have to track which tail
page was pinned. It leads to tricky and expensive get_page() on tail pages
and also occupy tail_page->_mapcount.

Most split_huge_page*() users want PMD to be split into table of PTEs and
don't care whether compound page is going to be split or not.

The plan is:

 - allow split_huge_page() to fail if the page is pinned. It's trivial to
   split non-pinned page and it doesn't require tail page refcounting, so
   tail_page->_mapcount is free to be reused.

 - introduce new routine -- split_huge_pmd() -- to split PMD into table of
   PTEs. It splits only one PMD, not touching other PMDs the page is
   mapped with or underlying compound page. Unlike new split_huge_page(),
   split_huge_pmd() never fails.

Fortunately, we have only few places where split_huge_page() is needed:
swap out, memory failure, migration, KSM. And all of them can handle
split_huge_page() fail.

In new scheme we use page->_mapcount is used to account how many time
the page is mapped with PTEs. We have separate compound_mapcount() to
count mappings with PMD. page_mapcount() returns sum of PTE and PMD
mappings of the page.

Introducing split_huge_pmd() effectively allows THP to be mapped with 4k.
It may be a surprise to some code to see a PTE which points to tail page
or VMA start/end in the middle of compound page.

munmap() part of THP will split PMD, but doesn't split the huge page. In
order to take memory consumption under control we put partially unmapped
huge page on list. The pages will be split by shrinker if memory pressure
comes. This way we also avoid unnecessary split_huge_page() on exit(2) if
a THP belong to more than one VMA.

= Refcounts and transparent huge pages =

  - get_page() and put_page() work *only* on head page's ->_count.
    We don't touch tail pages at all for these oprations. We stopped
    touching ->_mapcount in tail pages to store it's pins.

  - ->_count in tail pages is always zero: get_page_unless_zero() never
    succeed on tail pages. Nothing changed in this respect.

  - map/unmap of the pages with PTE entry increment/decrement ->_mapcount
    on relevent sub-page of the compound page.

  - map/unmap of the whole compound page accounted in compound_mapcount
    (stored in first tail page).

  - PageDoubleMap() indicates that ->_mapcount in all subpages is offset
    up by one. This additional reference is required to get race-free
    detection of unmap of subpages when we have them mapped with both PMDs
    and PTEs.

    This is optimization required to lower overhead of per-subpage
    mapcount tracking. The alternative is alter ->_mapcount in all
    subpages on each map/unmap of the whole compound page.

    We set PG_double_map when a PMD of the page got split for the first
    time, but still have PMD mapping. The addtional references go away
    with last compound_mapcount.

= Benchmarks =

Kernel build benchmark:

			baseline		v6

Amean    user-2       447.76 (  0.00%)      451.24 ( -0.78%)
Amean    user-4       314.94 (  0.00%)      310.10 (  1.54%)
Amean    user-8       388.91 (  0.00%)      388.95 ( -0.01%)
Amean    user-16      518.68 (  0.00%)      518.60 (  0.02%)
Amean    user-24      533.58 (  0.00%)      535.35 ( -0.33%)
Amean    syst-2        77.52 (  0.00%)       70.16 (  9.49%)
Amean    syst-4        51.21 (  0.00%)       44.55 ( 13.00%)
Amean    syst-8        42.12 (  0.00%)       42.59 ( -1.12%)
Amean    syst-16       50.29 (  0.00%)       50.14 (  0.30%)
Amean    syst-24       49.36 (  0.00%)       48.54 (  1.65%)
Amean    elsp-2       242.64 (  0.00%)      244.46 ( -0.75%)
Amean    elsp-4        93.78 (  0.00%)       92.89 (  0.95%)
Amean    elsp-8        61.51 (  0.00%)       61.92 ( -0.66%)
Amean    elsp-16       53.95 (  0.00%)       53.80 (  0.29%)
Amean    elsp-24       52.75 (  0.00%)       53.14 ( -0.74%)
Stddev   user-2        15.49 (  0.00%)       13.75 ( 11.24%)
Stddev   user-4         7.85 (  0.00%)        4.42 ( 43.68%)
Stddev   user-8         1.29 (  0.00%)        2.77 (-114.28%)
Stddev   user-16        2.56 (  0.00%)        1.54 ( 39.89%)
Stddev   user-24        1.75 (  0.00%)        1.06 ( 39.75%)
Stddev   syst-2         3.02 (  0.00%)        2.00 ( 33.86%)
Stddev   syst-4         1.23 (  0.00%)        0.91 ( 26.65%)
Stddev   syst-8         0.41 (  0.00%)        0.30 ( 28.32%)
Stddev   syst-16        0.51 (  0.00%)        0.71 (-38.07%)
Stddev   syst-24        0.92 (  0.00%)        0.70 ( 23.86%)
Stddev   elsp-2         8.70 (  0.00%)        7.99 (  8.13%)
Stddev   elsp-4         1.74 (  0.00%)        0.59 ( 66.08%)
Stddev   elsp-8         0.40 (  0.00%)        0.30 ( 25.11%)
Stddev   elsp-16        0.45 (  0.00%)        0.37 ( 17.73%)
Stddev   elsp-24        0.57 (  0.00%)        0.38 ( 33.64%)

Changes are mostly non-significant. The only noticble part is reduction of
system time for -j2 and -j4: 9.49% and 13.00%.

specjvm
                                    base                    v6
Ops compiler                   569.52 (  0.00%)       618.74 (  8.64%)
Ops compress                   456.32 (  0.00%)       469.20 (  2.82%)
Ops crypto                     424.34 (  0.00%)       413.64 ( -2.52%)
Ops derby                      535.15 (  0.00%)       536.96 (  0.34%)
Ops mpegaudio                  291.03 (  0.00%)       286.35 ( -1.61%)
Ops scimark.large               75.91 (  0.00%)        77.21 (  1.71%)
Ops scimark.small              529.19 (  0.00%)       527.07 ( -0.40%)
Ops serial                     316.13 (  0.00%)       316.40 (  0.09%)
Ops sunflow                    154.90 (  0.00%)       154.85 ( -0.03%)
Ops xml                        612.94 (  0.00%)       575.20 ( -6.16%)
Ops compiler.compiler          770.11 (  0.00%)       878.22 ( 14.04%)
Ops compiler.sunflow           421.17 (  0.00%)       435.92 (  3.50%)
Ops compress                   456.32 (  0.00%)       469.20 (  2.82%)
Ops crypto.aes                 153.17 (  0.00%)       151.30 ( -1.22%)
Ops crypto.rsa                 607.43 (  0.00%)       564.65 ( -7.04%)
Ops crypto.signverify          821.23 (  0.00%)       828.40 (  0.87%)
Ops derby                      535.15 (  0.00%)       536.96 (  0.34%)
Ops mpegaudio                  291.03 (  0.00%)       286.35 ( -1.61%)
Ops scimark.fft.large           69.59 (  0.00%)        69.81 (  0.32%)
Ops scimark.lu.large            20.31 (  0.00%)        20.32 (  0.05%)
Ops scimark.sor.large          114.57 (  0.00%)       113.99 ( -0.51%)
Ops scimark.sparse.large        55.56 (  0.00%)        61.71 ( 11.07%)
Ops scimark.monte_carlo        280.13 (  0.00%)       275.09 ( -1.80%)
Ops scimark.fft.small          815.19 (  0.00%)       819.55 (  0.53%)
Ops scimark.lu.small          1072.62 (  0.00%)      1081.47 (  0.83%)
Ops scimark.sor.small          674.47 (  0.00%)       674.24 ( -0.03%)
Ops scimark.sparse.small       251.20 (  0.00%)       247.43 ( -1.50%)
Ops serial                     316.13 (  0.00%)       316.40 (  0.09%)
Ops sunflow                    154.90 (  0.00%)       154.85 ( -0.03%)
Ops xml.transform              538.16 (  0.00%)       519.64 ( -3.44%)
Ops xml.validation             698.10 (  0.00%)       636.70 ( -8.80%)

Results are mixed.

= Patches overview =

Patch 1:
        We need to look on all subpages of compound page to calculate
        correct PSS, because they can have different mapcount.

Patch 2:
        With PTE-mapeed THP, rmap cannot rely on PageTransHuge() check to
        decide if map small page or THP. We need to get the info from
        caller.

Patch 3:
        Make memcg aware about new refcounting. Validation needed.

Patch 4:
        Adjust conditions when we can re-use the page on write-protection
        fault.

Patch 5:
        FOLL_SPLIT should be handled on PTE level too.

Patch 6:
	Make generic fast GUP implementation aware about PTE-mapped huge
	pages.

Patch 7:
        Split all pages in mlocked VMA. That should be good enough for
	now.

Patch 8:
        Make khugepaged aware about PTE-mapped huge pages.

Patch 9:
	Rename split_huge_page_pmd() to split_huge_pmd() to reflect that
	page is not going to be split, only PMD.

Patch 10:
        New THP_SPLIT_* vmstats.

Patch 11:
	Up to this point we tried to keep patchset bisectable, but next
	patches are going to change how core of THP refcounting work.
	That's easier to review change if we would disable THP temporally
	and bring it back once everything is ready.

Patch 12:
	Remove all split_huge_page()-related code. It also remove need in
	tail page refcounting.

Patch 13:
	Drop tail page refcounting. Diffstat is nice! :)

Patch 14:
        Remove ugly special case if futex happened to be in tail THP page.
        With new refcounting it much easier to protect against split.

Patch 15:
        Simplify KSM code which handle THP.

Patch 16:
	No need in compound_lock anymore.

Patches 17-25:
        Drop infrastructure for handling PMD splitting. We don't use it
        anymore in split_huge_page().

Patch 26:
        Store mapcount for compound pages separately: in the first tail
        page ->mapping.

Patch 27:
	Let's define page_mapped() to be true for compound pages if any
	sub-pages of the compound page is mapped (with PMD or PTE).

Patch 28:
	Make numabalancing aware about PTE-mapped THP.

Patch 29:
	Implement new split_huge_pmd().

Patch 30-32:
	Implement new split_huge_page().

Patch 33:
	Split pages instaed of PMDs on migrate_pages.

Patch 34:
        Handle partial unmap of THP. We put partially unmapped huge page
        list. Pages from list will split via shrinker if memory pressure
	comes. This way we also avoid unnecessary split_huge_page() on
        exit(2) if a THP belong to more than one VMA.

Patch 35:
	Everything is in place. Re-enable THP.

Patch 36:
        Documentation update.

The patchset also available on git:

git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git thp/refcounting/v10

Please review and consider applying.
Kirill A. Shutemov (36):
  mm, proc: adjust PSS calculation
  rmap: add argument to charge compound page
  memcg: adjust to support new THP refcounting
  mm, thp: adjust conditions when we can reuse the page on WP fault
  mm: adjust FOLL_SPLIT for new refcounting
  mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton
  thp, mlock: do not allow huge pages in mlocked area
  khugepaged: ignore pmd tables with THP mapped with ptes
  thp: rename split_huge_page_pmd() to split_huge_pmd()
  mm, vmstats: new THP splitting event
  mm: temporally mark THP broken
  thp: drop all split_huge_page()-related code
  mm: drop tail page refcounting
  futex, thp: remove special case for THP in get_futex_key
  ksm: prepare to new THP semantics
  mm, thp: remove compound_lock
  arm64, thp: remove infrastructure for handling splitting PMDs
  arm, thp: remove infrastructure for handling splitting PMDs
  mips, thp: remove infrastructure for handling splitting PMDs
  powerpc, thp: remove infrastructure for handling splitting PMDs
  s390, thp: remove infrastructure for handling splitting PMDs
  sparc, thp: remove infrastructure for handling splitting PMDs
  tile, thp: remove infrastructure for handling splitting PMDs
  x86, thp: remove infrastructure for handling splitting PMDs
  mm, thp: remove infrastructure for handling splitting PMDs
  mm: rework mapcount accounting to enable 4k mapping of THPs
  mm: differentiate page_mapped() from page_mapcount() for compound
    pages
  mm, numa: skip PTE-mapped THP on numa fault
  thp: implement split_huge_pmd()
  thp: add option to setup migration entries during PMD split
  thp, mm: split_huge_page(): caller need to lock page
  thp: reintroduce split_huge_page()
  migrate_pages: try to split pages on qeueuing
  thp: introduce deferred_split_huge_page()
  mm: re-enable THP
  thp: update documentation

 Documentation/vm/transhuge.txt           |  151 ++--
 arch/arc/mm/cache.c                      |    4 +-
 arch/arm/include/asm/pgtable-3level.h    |   10 -
 arch/arm/lib/uaccess_with_memcpy.c       |    5 +-
 arch/arm/mm/flush.c                      |   17 +-
 arch/arm64/include/asm/pgtable.h         |    8 -
 arch/arm64/mm/flush.c                    |   16 -
 arch/mips/include/asm/pgtable-bits.h     |    6 +-
 arch/mips/include/asm/pgtable.h          |   18 -
 arch/mips/mm/c-r4k.c                     |    3 +-
 arch/mips/mm/cache.c                     |    2 +-
 arch/mips/mm/gup.c                       |   17 +-
 arch/mips/mm/init.c                      |    6 +-
 arch/mips/mm/pgtable-64.c                |   14 -
 arch/mips/mm/tlbex.c                     |    1 -
 arch/powerpc/include/asm/pgtable-ppc64.h |   25 +-
 arch/powerpc/mm/hugepage-hash64.c        |    3 -
 arch/powerpc/mm/hugetlbpage.c            |   17 +-
 arch/powerpc/mm/pgtable_64.c             |   49 --
 arch/powerpc/mm/subpage-prot.c           |    2 +-
 arch/s390/include/asm/pgtable.h          |   15 +-
 arch/s390/mm/gup.c                       |   24 +-
 arch/s390/mm/pgtable.c                   |   16 -
 arch/sh/mm/cache-sh4.c                   |    2 +-
 arch/sh/mm/cache.c                       |    8 +-
 arch/sparc/include/asm/pgtable_64.h      |   16 -
 arch/sparc/mm/fault_64.c                 |    3 -
 arch/sparc/mm/gup.c                      |   16 +-
 arch/tile/include/asm/pgtable.h          |   10 -
 arch/x86/include/asm/pgtable.h           |    9 -
 arch/x86/include/asm/pgtable_types.h     |    2 -
 arch/x86/kernel/vm86_32.c                |    6 +-
 arch/x86/mm/gup.c                        |   17 +-
 arch/x86/mm/pgtable.c                    |   14 -
 arch/xtensa/mm/tlb.c                     |    2 +-
 fs/proc/page.c                           |    4 +-
 fs/proc/task_mmu.c                       |   55 +-
 include/asm-generic/pgtable.h            |    9 -
 include/linux/huge_mm.h                  |   56 +-
 include/linux/memcontrol.h               |   16 +-
 include/linux/mm.h                       |  116 ++--
 include/linux/mm_types.h                 |   20 +-
 include/linux/page-flags.h               |   49 +-
 include/linux/pagemap.h                  |   13 +-
 include/linux/rmap.h                     |   16 +-
 include/linux/swap.h                     |    3 +-
 include/linux/vm_event_item.h            |    4 +-
 kernel/events/uprobes.c                  |   11 +-
 kernel/futex.c                           |   61 +-
 mm/debug.c                               |    8 +-
 mm/filemap.c                             |   10 +-
 mm/gup.c                                 |  112 ++-
 mm/huge_memory.c                         | 1100 +++++++++++++++++-------------
 mm/hugetlb.c                             |   10 +-
 mm/internal.h                            |   70 +-
 mm/ksm.c                                 |   61 +-
 mm/madvise.c                             |    2 +-
 mm/memcontrol.c                          |   84 +--
 mm/memory-failure.c                      |    8 +-
 mm/memory.c                              |   73 +-
 mm/mempolicy.c                           |   37 +-
 mm/migrate.c                             |   19 +-
 mm/mincore.c                             |    2 +-
 mm/mlock.c                               |   51 +-
 mm/mprotect.c                            |    2 +-
 mm/mremap.c                              |   15 +-
 mm/page_alloc.c                          |   34 +-
 mm/pagewalk.c                            |    2 +-
 mm/pgtable-generic.c                     |   14 -
 mm/rmap.c                                |  163 +++--
 mm/shmem.c                               |   21 +-
 mm/swap.c                                |  273 +-------
 mm/swapfile.c                            |   16 +-
 mm/userfaultfd.c                         |    8 +-
 mm/vmstat.c                              |    4 +-
 75 files changed, 1367 insertions(+), 1799 deletions(-)

-- 
2.5.0

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#1218362 — [PATCHv10 23/36] tile, thp: remove infrastructure for handling splitting PMDs

With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/tile/include/asm/pgtable.h | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/arch/tile/include/asm/pgtable.h b/arch/tile/include/asm/pgtable.h
index 2b05ccbebed9..96cecf55522e 100644
--- a/arch/tile/include/asm/pgtable.h
+++ b/arch/tile/include/asm/pgtable.h
@@ -489,16 +489,6 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define has_transparent_hugepage() 1
 #define pmd_trans_huge pmd_huge_page
-
-static inline pmd_t pmd_mksplitting(pmd_t pmd)
-{
-	return pte_pmd(hv_pte_set_client2(pmd_pte(pmd)));
-}
-
-static inline int pmd_trans_splitting(pmd_t pmd)
-{
-	return hv_pte_get_client2(pmd_pte(pmd));
-}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 /*
-- 
2.5.0

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#1218363 — [PATCHv10 11/36] mm: temporally mark THP broken

Up to this point we tried to keep patchset bisectable, but next patches
are going to change how core of THP refcounting work.

It would be beneficial to split the change into several patches and make
it more reviewable. Unfortunately, I don't see how we can achieve that
while keeping THP working.

Let's hide THP under CONFIG_BROKEN for now and bring it back when new
refcounting get established.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index b9fb7a76a51d..45edc5a989ee 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -398,7 +398,7 @@ config NOMMU_INITIAL_TRIM_EXCESS
 
 config TRANSPARENT_HUGEPAGE
 	bool "Transparent Hugepage Support"
-	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
+	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && BROKEN
 	select COMPACTION
 	help
 	  Transparent Hugepages allows the kernel to use huge pages and
-- 
2.5.0

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#1218364 — [PATCHv10 12/36] thp: drop all split_huge_page()-related code

We will re-introduce new version with new refcounting later in patchset.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 include/linux/huge_mm.h |  28 +---
 mm/huge_memory.c        | 401 +-----------------------------------------------
 2 files changed, 7 insertions(+), 422 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 4e8b99d47661..87ea3723ff04 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -99,28 +99,12 @@ extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
 #endif /* CONFIG_DEBUG_VM */
 
 extern unsigned long transparent_hugepage_flags;
-extern int split_huge_page_to_list(struct page *page, struct list_head *list);
-static inline int split_huge_page(struct page *page)
-{
-	return split_huge_page_to_list(page, NULL);
-}
-extern void __split_huge_page_pmd(struct vm_area_struct *vma,
-		unsigned long address, pmd_t *pmd);
-#define split_huge_pmd(__vma, __pmd, __address)				\
-	do {								\
-		pmd_t *____pmd = (__pmd);				\
-		if (unlikely(pmd_trans_huge(*____pmd)))			\
-			__split_huge_page_pmd(__vma, __address,		\
-					____pmd);			\
-	}  while (0)
-#define wait_split_huge_page(__anon_vma, __pmd)				\
-	do {								\
-		pmd_t *____pmd = (__pmd);				\
-		anon_vma_lock_write(__anon_vma);			\
-		anon_vma_unlock_write(__anon_vma);			\
-		BUG_ON(pmd_trans_splitting(*____pmd) ||			\
-		       pmd_trans_huge(*____pmd));			\
-	} while (0)
+
+#define split_huge_page_to_list(page, list) BUILD_BUG()
+#define split_huge_page(page) BUILD_BUG()
+#define split_huge_pmd(__vma, __pmd, __address) BUILD_BUG()
+
+#define wait_split_huge_page(__anon_vma, __pmd) BUILD_BUG()
 #if HPAGE_PMD_ORDER >= MAX_ORDER
 #error "hugepages can't be allocated by the buddy allocator"
 #endif
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ac1948397d6f..2a030f1aebf6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1717,328 +1717,6 @@ int pmd_freeable(pmd_t pmd)
 	return !pmd_dirty(pmd);
 }
 
-static int __split_huge_page_splitting(struct page *page,
-				       struct vm_area_struct *vma,
-				       unsigned long address)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	spinlock_t *ptl;
-	pmd_t *pmd;
-	int ret = 0;
-	/* For mmu_notifiers */
-	const unsigned long mmun_start = address;
-	const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
-
-	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
-	pmd = page_check_address_pmd(page, mm, address,
-			PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
-	if (pmd) {
-		/*
-		 * We can't temporarily set the pmd to null in order
-		 * to split it, the pmd must remain marked huge at all
-		 * times or the VM won't take the pmd_trans_huge paths
-		 * and it won't wait on the anon_vma->root->rwsem to
-		 * serialize against split_huge_page*.
-		 */
-		pmdp_splitting_flush(vma, address, pmd);
-
-		ret = 1;
-		spin_unlock(ptl);
-	}
-	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
-
-	return ret;
-}
-
-static void __split_huge_page_refcount(struct page *page,
-				       struct list_head *list)
-{
-	int i;
-	struct zone *zone = page_zone(page);
-	struct lruvec *lruvec;
-	int tail_count = 0;
-
-	/* prevent PageLRU to go away from under us, and freeze lru stats */
-	spin_lock_irq(&zone->lru_lock);
-	lruvec = mem_cgroup_page_lruvec(page, zone);
-
-	compound_lock(page);
-	/* complete memcg works before add pages to LRU */
-	mem_cgroup_split_huge_fixup(page);
-
-	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
-		struct page *page_tail = page + i;
-
-		/* tail_page->_mapcount cannot change */
-		BUG_ON(page_mapcount(page_tail) < 0);
-		tail_count += page_mapcount(page_tail);
-		/* check for overflow */
-		BUG_ON(tail_count < 0);
-		BUG_ON(atomic_read(&page_tail->_count) != 0);
-		/*
-		 * tail_page->_count is zero and not changing from
-		 * under us. But get_page_unless_zero() may be running
-		 * from under us on the tail_page. If we used
-		 * atomic_set() below instead of atomic_add(), we
-		 * would then run atomic_set() concurrently with
-		 * get_page_unless_zero(), and atomic_set() is
-		 * implemented in C not using locked ops. spin_unlock
-		 * on x86 sometime uses locked ops because of PPro
-		 * errata 66, 92, so unless somebody can guarantee
-		 * atomic_set() here would be safe on all archs (and
-		 * not only on x86), it's safer to use atomic_add().
-		 */
-		atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
-			   &page_tail->_count);
-
-		/* after clearing PageTail the gup refcount can be released */
-		smp_mb__after_atomic();
-
-		page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
-		page_tail->flags |= (page->flags &
-				     ((1L << PG_referenced) |
-				      (1L << PG_swapbacked) |
-				      (1L << PG_mlocked) |
-				      (1L << PG_uptodate) |
-				      (1L << PG_active) |
-				      (1L << PG_unevictable)));
-		page_tail->flags |= (1L << PG_dirty);
-
-		clear_compound_head(page_tail);
-
-		if (page_is_young(page))
-			set_page_young(page_tail);
-		if (page_is_idle(page))
-			set_page_idle(page_tail);
-
-		/*
-		 * __split_huge_page_splitting() already set the
-		 * splitting bit in all pmd that could map this
-		 * hugepage, that will ensure no CPU can alter the
-		 * mapcount on the head page. The mapcount is only
-		 * accounted in the head page and it has to be
-		 * transferred to all tail pages in the below code. So
-		 * for this code to be safe, the split the mapcount
-		 * can't change. But that doesn't mean userland can't
-		 * keep changing and reading the page contents while
-		 * we transfer the mapcount, so the pmd splitting
-		 * status is achieved setting a reserved bit in the
-		 * pmd, not by clearing the present bit.
-		*/
-		page_tail->_mapcount = page->_mapcount;
-
-		BUG_ON(page_tail->mapping != TAIL_MAPPING);
-		page_tail->mapping = page->mapping;
-
-		page_tail->index = page->index + i;
-		page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
-
-		BUG_ON(!PageAnon(page_tail));
-		BUG_ON(!PageUptodate(page_tail));
-		BUG_ON(!PageDirty(page_tail));
-		BUG_ON(!PageSwapBacked(page_tail));
-
-		lru_add_page_tail(page, page_tail, lruvec, list);
-	}
-	atomic_sub(tail_count, &page->_count);
-	BUG_ON(atomic_read(&page->_count) <= 0);
-
-	__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
-
-	ClearPageCompound(page);
-	compound_unlock(page);
-	spin_unlock_irq(&zone->lru_lock);
-
-	for (i = 1; i < HPAGE_PMD_NR; i++) {
-		struct page *page_tail = page + i;
-		BUG_ON(page_count(page_tail) <= 0);
-		/*
-		 * Tail pages may be freed if there wasn't any mapping
-		 * like if add_to_swap() is running on a lru page that
-		 * had its mapping zapped. And freeing these pages
-		 * requires taking the lru_lock so we do the put_page
-		 * of the tail pages after the split is complete.
-		 */
-		put_page(page_tail);
-	}
-
-	/*
-	 * Only the head page (now become a regular page) is required
-	 * to be pinned by the caller.
-	 */
-	BUG_ON(page_count(page) <= 0);
-}
-
-static int __split_huge_page_map(struct page *page,
-				 struct vm_area_struct *vma,
-				 unsigned long address)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	spinlock_t *ptl;
-	pmd_t *pmd, _pmd;
-	int ret = 0, i;
-	pgtable_t pgtable;
-	unsigned long haddr;
-
-	pmd = page_check_address_pmd(page, mm, address,
-			PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
-	if (pmd) {
-		pgtable = pgtable_trans_huge_withdraw(mm, pmd);
-		pmd_populate(mm, &_pmd, pgtable);
-		if (pmd_write(*pmd))
-			BUG_ON(page_mapcount(page) != 1);
-
-		haddr = address;
-		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
-			pte_t *pte, entry;
-			BUG_ON(PageCompound(page+i));
-			/*
-			 * Note that NUMA hinting access restrictions are not
-			 * transferred to avoid any possibility of altering
-			 * permissions across VMAs.
-			 */
-			entry = mk_pte(page + i, vma->vm_page_prot);
-			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-			if (!pmd_write(*pmd))
-				entry = pte_wrprotect(entry);
-			if (!pmd_young(*pmd))
-				entry = pte_mkold(entry);
-			pte = pte_offset_map(&_pmd, haddr);
-			BUG_ON(!pte_none(*pte));
-			set_pte_at(mm, haddr, pte, entry);
-			pte_unmap(pte);
-		}
-
-		smp_wmb(); /* make pte visible before pmd */
-		/*
-		 * Up to this point the pmd is present and huge and
-		 * userland has the whole access to the hugepage
-		 * during the split (which happens in place). If we
-		 * overwrite the pmd with the not-huge version
-		 * pointing to the pte here (which of course we could
-		 * if all CPUs were bug free), userland could trigger
-		 * a small page size TLB miss on the small sized TLB
-		 * while the hugepage TLB entry is still established
-		 * in the huge TLB. Some CPU doesn't like that. See
-		 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
-		 * Erratum 383 on page 93. Intel should be safe but is
-		 * also warns that it's only safe if the permission
-		 * and cache attributes of the two entries loaded in
-		 * the two TLB is identical (which should be the case
-		 * here). But it is generally safer to never allow
-		 * small and huge TLB entries for the same virtual
-		 * address to be loaded simultaneously. So instead of
-		 * doing "pmd_populate(); flush_tlb_range();" we first
-		 * mark the current pmd notpresent (atomically because
-		 * here the pmd_trans_huge and pmd_trans_splitting
-		 * must remain set at all times on the pmd until the
-		 * split is complete for this pmd), then we flush the
-		 * SMP TLB and finally we write the non-huge version
-		 * of the pmd entry with pmd_populate.
-		 */
-		pmdp_invalidate(vma, address, pmd);
-		pmd_populate(mm, pmd, pgtable);
-		ret = 1;
-		spin_unlock(ptl);
-	}
-
-	return ret;
-}
-
-/* must be called with anon_vma->root->rwsem held */
-static void __split_huge_page(struct page *page,
-			      struct anon_vma *anon_vma,
-			      struct list_head *list)
-{
-	int mapcount, mapcount2;
-	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
-	struct anon_vma_chain *avc;
-
-	BUG_ON(!PageHead(page));
-	BUG_ON(PageTail(page));
-
-	mapcount = 0;
-	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
-		struct vm_area_struct *vma = avc->vma;
-		unsigned long addr = vma_address(page, vma);
-		BUG_ON(is_vma_temporary_stack(vma));
-		mapcount += __split_huge_page_splitting(page, vma, addr);
-	}
-	/*
-	 * It is critical that new vmas are added to the tail of the
-	 * anon_vma list. This guarantes that if copy_huge_pmd() runs
-	 * and establishes a child pmd before
-	 * __split_huge_page_splitting() freezes the parent pmd (so if
-	 * we fail to prevent copy_huge_pmd() from running until the
-	 * whole __split_huge_page() is complete), we will still see
-	 * the newly established pmd of the child later during the
-	 * walk, to be able to set it as pmd_trans_splitting too.
-	 */
-	if (mapcount != page_mapcount(page)) {
-		pr_err("mapcount %d page_mapcount %d\n",
-			mapcount, page_mapcount(page));
-		BUG();
-	}
-
-	__split_huge_page_refcount(page, list);
-
-	mapcount2 = 0;
-	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
-		struct vm_area_struct *vma = avc->vma;
-		unsigned long addr = vma_address(page, vma);
-		BUG_ON(is_vma_temporary_stack(vma));
-		mapcount2 += __split_huge_page_map(page, vma, addr);
-	}
-	if (mapcount != mapcount2) {
-		pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
-			mapcount, mapcount2, page_mapcount(page));
-		BUG();
-	}
-}
-
-/*
- * Split a hugepage into normal pages. This doesn't change the position of head
- * page. If @list is null, tail pages will be added to LRU list, otherwise, to
- * @list. Both head page and tail pages will inherit mapping, flags, and so on
- * from the hugepage.
- * Return 0 if the hugepage is split successfully otherwise return 1.
- */
-int split_huge_page_to_list(struct page *page, struct list_head *list)
-{
-	struct anon_vma *anon_vma;
-	int ret = 1;
-
-	BUG_ON(is_huge_zero_page(page));
-	BUG_ON(!PageAnon(page));
-
-	/*
-	 * The caller does not necessarily hold an mmap_sem that would prevent
-	 * the anon_vma disappearing so we first we take a reference to it
-	 * and then lock the anon_vma for write. This is similar to
-	 * page_lock_anon_vma_read except the write lock is taken to serialise
-	 * against parallel split or collapse operations.
-	 */
-	anon_vma = page_get_anon_vma(page);
-	if (!anon_vma)
-		goto out;
-	anon_vma_lock_write(anon_vma);
-
-	ret = 0;
-	if (!PageCompound(page))
-		goto out_unlock;
-
-	BUG_ON(!PageSwapBacked(page));
-	__split_huge_page(page, anon_vma, list);
-	count_vm_event(THP_SPLIT_PAGE);
-
-	BUG_ON(PageCompound(page));
-out_unlock:
-	anon_vma_unlock_write(anon_vma);
-	put_anon_vma(anon_vma);
-out:
-	return ret;
-}
-
 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
 
 int hugepage_madvise(struct vm_area_struct *vma,
@@ -2984,83 +2662,6 @@ static int khugepaged(void *none)
 	return 0;
 }
 
-static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
-		unsigned long haddr, pmd_t *pmd)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	pgtable_t pgtable;
-	pmd_t _pmd;
-	int i;
-
-	pmdp_huge_clear_flush_notify(vma, haddr, pmd);
-	/* leave pmd empty until pte is filled */
-
-	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
-	pmd_populate(mm, &_pmd, pgtable);
-
-	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
-		pte_t *pte, entry;
-		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
-		entry = pte_mkspecial(entry);
-		pte = pte_offset_map(&_pmd, haddr);
-		VM_BUG_ON(!pte_none(*pte));
-		set_pte_at(mm, haddr, pte, entry);
-		pte_unmap(pte);
-	}
-	smp_wmb(); /* make pte visible before pmd */
-	pmd_populate(mm, pmd, pgtable);
-	put_huge_zero_page();
-}
-
-void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
-		pmd_t *pmd)
-{
-	spinlock_t *ptl;
-	struct page *page = NULL;
-	struct mm_struct *mm = vma->vm_mm;
-	unsigned long haddr = address & HPAGE_PMD_MASK;
-	unsigned long mmun_start;	/* For mmu_notifiers */
-	unsigned long mmun_end;		/* For mmu_notifiers */
-
-	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
-
-	mmun_start = haddr;
-	mmun_end   = haddr + HPAGE_PMD_SIZE;
-again:
-	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
-	ptl = pmd_lock(mm, pmd);
-	if (unlikely(!pmd_trans_huge(*pmd)))
-		goto unlock;
-	if (vma_is_dax(vma)) {
-		pmd_t _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
-		if (is_huge_zero_pmd(_pmd))
-			put_huge_zero_page();
-	} else if (is_huge_zero_pmd(*pmd)) {
-		__split_huge_zero_page_pmd(vma, haddr, pmd);
-	} else {
-		page = pmd_page(*pmd);
-		VM_BUG_ON_PAGE(!page_count(page), page);
-		get_page(page);
-	}
- unlock:
-	spin_unlock(ptl);
-	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
-
-	if (!page)
-		return;
-
-	split_huge_page(page);
-	put_page(page);
-
-	/*
-	 * We don't always have down_write of mmap_sem here: a racing
-	 * do_huge_pmd_wp_page() might have copied-on-write to another
-	 * huge page before our split_huge_page() got the anon_vma lock.
-	 */
-	if (unlikely(pmd_trans_huge(*pmd)))
-		goto again;
-}
-
 static void split_huge_pmd_address(struct vm_area_struct *vma,
 				    unsigned long address)
 {
@@ -3085,7 +2686,7 @@ static void split_huge_pmd_address(struct vm_area_struct *vma,
 	 * Caller holds the mmap_sem write mode, so a huge pmd cannot
 	 * materialize from under us.
 	 */
-	__split_huge_page_pmd(vma, address, pmd);
+	split_huge_pmd(vma, pmd, address);
 }
 
 void vma_adjust_trans_huge(struct vm_area_struct *vma,
-- 
2.5.0

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#1218368 — [PATCHv10 05/36] mm: adjust FOLL_SPLIT for new refcounting

We need to prepare kernel to allow transhuge pages to be mapped with
ptes too. We need to handle FOLL_SPLIT in follow_page_pte().

Also we use split_huge_page() directly instead of split_huge_page_pmd().
split_huge_page_pmd() will gone.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/gup.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 49 insertions(+), 18 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index deafa2c91b36..745a50f2d57d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -116,6 +116,19 @@ retry:
 		}
 	}
 
+	if (flags & FOLL_SPLIT && PageTransCompound(page)) {
+		int ret;
+		get_page(page);
+		pte_unmap_unlock(ptep, ptl);
+		lock_page(page);
+		ret = split_huge_page(page);
+		unlock_page(page);
+		put_page(page);
+		if (ret)
+			return ERR_PTR(ret);
+		goto retry;
+	}
+
 	if (flags & FOLL_GET)
 		get_page_foll(page);
 	if (flags & FOLL_TOUCH) {
@@ -220,27 +233,45 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
 	}
 	if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
 		return no_page_table(vma, flags);
-	if (pmd_trans_huge(*pmd)) {
-		if (flags & FOLL_SPLIT) {
+	if (likely(!pmd_trans_huge(*pmd)))
+		return follow_page_pte(vma, address, pmd, flags);
+
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_trans_huge(*pmd))) {
+		spin_unlock(ptl);
+		return follow_page_pte(vma, address, pmd, flags);
+	}
+
+	if (unlikely(pmd_trans_splitting(*pmd))) {
+		spin_unlock(ptl);
+		wait_split_huge_page(vma->anon_vma, pmd);
+		return follow_page_pte(vma, address, pmd, flags);
+	}
+
+	if (flags & FOLL_SPLIT) {
+		int ret;
+		page = pmd_page(*pmd);
+		if (is_huge_zero_page(page)) {
+			spin_unlock(ptl);
+			ret = 0;
 			split_huge_page_pmd(vma, address, pmd);
-			return follow_page_pte(vma, address, pmd, flags);
-		}
-		ptl = pmd_lock(mm, pmd);
-		if (likely(pmd_trans_huge(*pmd))) {
-			if (unlikely(pmd_trans_splitting(*pmd))) {
-				spin_unlock(ptl);
-				wait_split_huge_page(vma->anon_vma, pmd);
-			} else {
-				page = follow_trans_huge_pmd(vma, address,
-							     pmd, flags);
-				spin_unlock(ptl);
-				*page_mask = HPAGE_PMD_NR - 1;
-				return page;
-			}
-		} else
+		} else {
+			get_page(page);
 			spin_unlock(ptl);
+			lock_page(page);
+			ret = split_huge_page(page);
+			unlock_page(page);
+			put_page(page);
+		}
+
+		return ret ? ERR_PTR(ret) :
+			follow_page_pte(vma, address, pmd, flags);
 	}
-	return follow_page_pte(vma, address, pmd, flags);
+
+	page = follow_trans_huge_pmd(vma, address, pmd, flags);
+	spin_unlock(ptl);
+	*page_mask = HPAGE_PMD_NR - 1;
+	return page;
 }
 
 static int get_gate_page(struct mm_struct *mm, unsigned long address,
-- 
2.5.0

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#1218369 — [PATCHv10 20/36] powerpc, thp: remove infrastructure for handling splitting PMDs

With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.

pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/pgtable-ppc64.h | 25 +---------------
 arch/powerpc/mm/hugepage-hash64.c        |  3 --
 arch/powerpc/mm/hugetlbpage.c            |  4 ---
 arch/powerpc/mm/pgtable_64.c             | 49 --------------------------------
 4 files changed, 1 insertion(+), 80 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
index 42886fc772df..6de43b646d1f 100644
--- a/arch/powerpc/include/asm/pgtable-ppc64.h
+++ b/arch/powerpc/include/asm/pgtable-ppc64.h
@@ -374,11 +374,6 @@ void pgtable_cache_init(void);
 #endif /* __ASSEMBLY__ */
 
 /*
- * THP pages can't be special. So use the _PAGE_SPECIAL
- */
-#define _PAGE_SPLITTING _PAGE_SPECIAL
-
-/*
  * We need to differentiate between explicit huge page and THP huge
  * page, since THP huge page also need to track real subpage details
  */
@@ -388,8 +383,7 @@ void pgtable_cache_init(void);
  * set of bits not changed in pmd_modify.
  */
 #define _HPAGE_CHG_MASK (PTE_RPN_MASK | _PAGE_HPTEFLAGS |		\
-			 _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_SPLITTING | \
-			 _PAGE_THP_HUGE)
+			 _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_THP_HUGE)
 
 #ifndef __ASSEMBLY__
 /*
@@ -471,13 +465,6 @@ static inline int pmd_trans_huge(pmd_t pmd)
 	return (pmd_val(pmd) & 0x3) && (pmd_val(pmd) & _PAGE_THP_HUGE);
 }
 
-static inline int pmd_trans_splitting(pmd_t pmd)
-{
-	if (pmd_trans_huge(pmd))
-		return pmd_val(pmd) & _PAGE_SPLITTING;
-	return 0;
-}
-
 extern int has_transparent_hugepage(void);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
@@ -530,12 +517,6 @@ static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 	return pmd;
 }
 
-static inline pmd_t pmd_mksplitting(pmd_t pmd)
-{
-	pmd_val(pmd) |= _PAGE_SPLITTING;
-	return pmd;
-}
-
 #define __HAVE_ARCH_PMD_SAME
 static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 {
@@ -586,10 +567,6 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm, unsigned long addr,
 	pmd_hugepage_update(mm, addr, pmdp, _PAGE_RW, 0);
 }
 
-#define __HAVE_ARCH_PMDP_SPLITTING_FLUSH
-extern void pmdp_splitting_flush(struct vm_area_struct *vma,
-				 unsigned long address, pmd_t *pmdp);
-
 extern pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
 				 unsigned long address, pmd_t *pmdp);
 #define pmdp_collapse_flush pmdp_collapse_flush
diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index 43dafb9d6a46..adc3860ce9e7 100644
--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -39,9 +39,6 @@ int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
 		/* If PMD busy, retry the access */
 		if (unlikely(old_pmd & _PAGE_BUSY))
 			return 0;
-		/* If PMD is trans splitting retry the access */
-		if (unlikely(old_pmd & _PAGE_SPLITTING))
-			return 0;
 		/* If PMD permissions don't match, take page fault */
 		if (unlikely(access & ~old_pmd))
 			return 1;
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index f357eec834e3..fa9aa18ae159 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -1015,10 +1015,6 @@ pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
 			/*
 			 * A hugepage collapse is captured by pmd_none, because
 			 * it mark the pmd none and do a hpte invalidate.
-			 *
-			 * We don't worry about pmd_trans_splitting here, The
-			 * caller if it needs to handle the splitting case
-			 * should check for that.
 			 */
 			if (pmd_none(pmd))
 				return NULL;
diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index 876232d64126..ac8f12d3cfce 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -614,55 +614,6 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 }
 
 /*
- * We mark the pmd splitting and invalidate all the hpte
- * entries for this hugepage.
- */
-void pmdp_splitting_flush(struct vm_area_struct *vma,
-			  unsigned long address, pmd_t *pmdp)
-{
-	unsigned long old, tmp;
-
-	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
-
-#ifdef CONFIG_DEBUG_VM
-	WARN_ON(!pmd_trans_huge(*pmdp));
-	assert_spin_locked(&vma->vm_mm->page_table_lock);
-#endif
-
-#ifdef PTE_ATOMIC_UPDATES
-
-	__asm__ __volatile__(
-	"1:	ldarx	%0,0,%3\n\
-		andi.	%1,%0,%6\n\
-		bne-	1b \n\
-		ori	%1,%0,%4 \n\
-		stdcx.	%1,0,%3 \n\
-		bne-	1b"
-	: "=&r" (old), "=&r" (tmp), "=m" (*pmdp)
-	: "r" (pmdp), "i" (_PAGE_SPLITTING), "m" (*pmdp), "i" (_PAGE_BUSY)
-	: "cc" );
-#else
-	old = pmd_val(*pmdp);
-	*pmdp = __pmd(old | _PAGE_SPLITTING);
-#endif
-	/*
-	 * If we didn't had the splitting flag set, go and flush the
-	 * HPTE entries.
-	 */
-	trace_hugepage_splitting(address, old);
-	if (!(old & _PAGE_SPLITTING)) {
-		/* We need to flush the hpte */
-		if (old & _PAGE_HASHPTE)
-			hpte_do_hugepage_flush(vma->vm_mm, address, pmdp, old);
-	}
-	/*
-	 * This ensures that generic code that rely on IRQ disabling
-	 * to prevent a parallel THP split work as expected.
-	 */
-	kick_all_cpus_sync();
-}
-
-/*
  * We want to put the pgtable in pmd and use pgtable for tracking
  * the base page size hptes
  */
-- 
2.5.0

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#1218371 — [PATCHv10 31/36] thp, mm: split_huge_page(): caller need to lock page

We're going to use migration entries instead of compound_lock() to
stabilize page refcounts. Setup and remove migration entries require
page to be locked.

Some of split_huge_page() callers already have the page locked. Let's
require everybody to lock the page before calling split_huge_page().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/memory-failure.c | 8 +++++++-
 mm/migrate.c        | 8 ++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 39591cce45ca..216f1d4768ec 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1148,7 +1148,9 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	}
 
 	if (!PageHuge(p) && PageTransHuge(hpage)) {
+		lock_page(hpage);
 		if (!PageAnon(hpage) || unlikely(split_huge_page(hpage))) {
+			unlock_page(hpage);
 			if (!PageAnon(hpage))
 				pr_err("MCE: %#lx: non anonymous thp\n", pfn);
 			else
@@ -1158,6 +1160,7 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 			put_hwpoison_page(p);
 			return -EBUSY;
 		}
+		unlock_page(hpage);
 		VM_BUG_ON_PAGE(!page_count(p), p);
 		hpage = compound_head(p);
 	}
@@ -1735,7 +1738,10 @@ int soft_offline_page(struct page *page, int flags)
 		return -EBUSY;
 	}
 	if (!PageHuge(page) && PageTransHuge(hpage)) {
-		if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
+		lock_page(page);
+		ret = split_huge_page(hpage);
+		unlock_page(page);
+		if (unlikely(ret)) {
 			pr_info("soft offline: %#lx: failed to split THP\n",
 				pfn);
 			if (flags & MF_COUNT_INCREASED)
diff --git a/mm/migrate.c b/mm/migrate.c
index d63965e2733d..b8e968fab1d2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -939,9 +939,13 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		goto out;
 	}
 
-	if (unlikely(PageTransHuge(page)))
-		if (unlikely(split_huge_page(page)))
+	if (unlikely(PageTransHuge(page))) {
+		lock_page(page);
+		rc = split_huge_page(page);
+		unlock_page(page);
+		if (rc)
 			goto out;
+	}
 
 	rc = __unmap_and_move(page, newpage, force, mode);
 
-- 
2.5.0

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#1218372 — [PATCHv10 18/36] arm, thp: remove infrastructure for handling splitting PMDs

With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.

pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/arm/include/asm/pgtable-3level.h | 10 ----------
 arch/arm/lib/uaccess_with_memcpy.c    |  5 ++---
 arch/arm/mm/flush.c                   | 15 ---------------
 3 files changed, 2 insertions(+), 28 deletions(-)

diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index 6d6012a320b2..d42f81f13618 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -88,7 +88,6 @@
 
 #define L_PMD_SECT_VALID	(_AT(pmdval_t, 1) << 0)
 #define L_PMD_SECT_DIRTY	(_AT(pmdval_t, 1) << 55)
-#define L_PMD_SECT_SPLITTING	(_AT(pmdval_t, 1) << 56)
 #define L_PMD_SECT_NONE		(_AT(pmdval_t, 1) << 57)
 #define L_PMD_SECT_RDONLY	(_AT(pteval_t, 1) << 58)
 
@@ -232,21 +231,12 @@ static inline pte_t pte_mkspecial(pte_t pte)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define pmd_trans_huge(pmd)	(pmd_val(pmd) && !pmd_table(pmd))
-#define pmd_trans_splitting(pmd) (pmd_isset((pmd), L_PMD_SECT_SPLITTING))
-
-#ifdef CONFIG_HAVE_RCU_TABLE_FREE
-#define __HAVE_ARCH_PMDP_SPLITTING_FLUSH
-void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
-			  pmd_t *pmdp);
-#endif
-#endif
 
 #define PMD_BIT_FUNC(fn,op) \
 static inline pmd_t pmd_##fn(pmd_t pmd) { pmd_val(pmd) op; return pmd; }
 
 PMD_BIT_FUNC(wrprotect,	|= L_PMD_SECT_RDONLY);
 PMD_BIT_FUNC(mkold,	&= ~PMD_SECT_AF);
-PMD_BIT_FUNC(mksplitting, |= L_PMD_SECT_SPLITTING);
 PMD_BIT_FUNC(mkwrite,   &= ~L_PMD_SECT_RDONLY);
 PMD_BIT_FUNC(mkdirty,   |= L_PMD_SECT_DIRTY);
 PMD_BIT_FUNC(mkclean,   &= ~L_PMD_SECT_DIRTY);
diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index 4b39af2dfda9..e51f6daa9650 100644
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -52,14 +52,13 @@ pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
 	 *
 	 * Lock the page table for the destination and check
 	 * to see that it's still huge and whether or not we will
-	 * need to fault on write, or if we have a splitting THP.
+	 * need to fault on write.
 	 */
 	if (unlikely(pmd_thp_or_huge(*pmd))) {
 		ptl = &current->mm->page_table_lock;
 		spin_lock(ptl);
 		if (unlikely(!pmd_thp_or_huge(*pmd)
-			|| pmd_hugewillfault(*pmd)
-			|| pmd_trans_splitting(*pmd))) {
+			|| pmd_hugewillfault(*pmd))) {
 			spin_unlock(ptl);
 			return 0;
 		}
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 34b66af516ea..77f229302032 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -400,18 +400,3 @@ void __flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned l
 	 */
 	__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
 }
-
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#ifdef CONFIG_HAVE_RCU_TABLE_FREE
-void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
-			  pmd_t *pmdp)
-{
-	pmd_t pmd = pmd_mksplitting(*pmdp);
-	VM_BUG_ON(address & ~PMD_MASK);
-	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
-
-	/* dummy IPI to serialise against fast_gup */
-	kick_all_cpus_sync();
-}
-#endif /* CONFIG_HAVE_RCU_TABLE_FREE */
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
-- 
2.5.0

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#1218373 — [PATCHv10 04/36] mm, thp: adjust conditions when we can reuse the page on WP fault

With new refcounting we will be able map the same compound page with
PTEs and PMDs. It requires adjustment to conditions when we can reuse
the page on write-protection fault.

For PTE fault we can't reuse the page if it's part of huge page.

For PMD we can only reuse the page if nobody else maps the huge page or
it's part. We can do it by checking page_mapcount() on each sub-page,
but it's expensive.

The cheaper way is to check page_count() to be equal 1: every mapcount
takes page reference, so this way we can guarantee, that the PMD is the
only mapping.

This approach can give false negative if somebody pinned the page, but
that doesn't affect correctness.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/swap.h |  3 ++-
 mm/huge_memory.c     | 12 +++++++++++-
 mm/swapfile.c        |  3 +++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 9c7c4b418498..1184fdbd30ba 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -540,7 +540,8 @@ static inline int swp_swapcount(swp_entry_t entry)
 	return 0;
 }
 
-#define reuse_swap_page(page)	(page_mapcount(page) == 1)
+#define reuse_swap_page(page) \
+	(!PageTransCompound(page) && page_mapcount(page) == 1)
 
 static inline int try_to_free_swap(struct page *page)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ad7c378e1f8c..18931b8ef1e7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1172,7 +1172,17 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	page = pmd_page(orig_pmd);
 	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
-	if (page_mapcount(page) == 1) {
+	/*
+	 * We can only reuse the page if nobody else maps the huge page or it's
+	 * part. We can do it by checking page_mapcount() on each sub-page, but
+	 * it's expensive.
+	 * The cheaper way is to check page_count() to be equal 1: every
+	 * mapcount takes page reference reference, so this way we can
+	 * guarantee, that the PMD is the only mapping.
+	 * This can give false negative if somebody pinned the page, but that's
+	 * fine.
+	 */
+	if (page_mapcount(page) == 1 && page_count(page) == 1) {
 		pmd_t entry;
 		entry = pmd_mkyoung(orig_pmd);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f131bc1838d3..c6aec93c8c0b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -929,6 +929,9 @@ int reuse_swap_page(struct page *page)
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	if (unlikely(PageKsm(page)))
 		return 0;
+	/* The page is part of THP and cannot be reused */
+	if (PageTransCompound(page))
+		return 0;
 	count = page_mapcount(page);
 	if (count <= 1 && PageSwapCache(page)) {
 		count += page_swapcount(page);
-- 
2.5.0

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#1218374 — [PATCHv10 16/36] mm, thp: remove compound_lock

We are going to use migration entries to stabilize page counts. It means
we don't need compound_lock() for that.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 include/linux/mm.h         | 35 -----------------------------------
 include/linux/page-flags.h | 12 +-----------
 mm/debug.c                 |  3 ---
 mm/memcontrol.c            | 11 +++--------
 4 files changed, 4 insertions(+), 57 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c3a1fd44cd0a..9fc4367eb591 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -384,41 +384,6 @@ static inline int is_vmalloc_or_module_addr(const void *x)
 
 extern void kvfree(const void *addr);
 
-static inline void compound_lock(struct page *page)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	VM_BUG_ON_PAGE(PageSlab(page), page);
-	bit_spin_lock(PG_compound_lock, &page->flags);
-#endif
-}
-
-static inline void compound_unlock(struct page *page)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	VM_BUG_ON_PAGE(PageSlab(page), page);
-	bit_spin_unlock(PG_compound_lock, &page->flags);
-#endif
-}
-
-static inline unsigned long compound_lock_irqsave(struct page *page)
-{
-	unsigned long uninitialized_var(flags);
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	local_irq_save(flags);
-	compound_lock(page);
-#endif
-	return flags;
-}
-
-static inline void compound_unlock_irqrestore(struct page *page,
-					      unsigned long flags)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	compound_unlock(page);
-	local_irq_restore(flags);
-#endif
-}
-
 /*
  * The atomic page->_mapcount, starts from -1: so that transitions
  * both from it and to it can be tracked, using atomic_inc_and_test
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ab1a0e9c5087..125f8cbf2c9a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -101,9 +101,6 @@ enum pageflags {
 #ifdef CONFIG_MEMORY_FAILURE
 	PG_hwpoison,		/* hardware poisoned page. Don't touch */
 #endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	PG_compound_lock,
-#endif
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
 	PG_young,
 	PG_idle,
@@ -611,12 +608,6 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
 #define __PG_MLOCKED		0
 #endif
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define __PG_COMPOUND_LOCK		(1 << PG_compound_lock)
-#else
-#define __PG_COMPOUND_LOCK		0
-#endif
-
 /*
  * Flags checked when a page is freed.  Pages being freed should not have
  * these flags set.  It they are, there is a problem.
@@ -626,8 +617,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
 	 1 << PG_private | 1 << PG_private_2 | \
 	 1 << PG_writeback | 1 << PG_reserved | \
 	 1 << PG_slab	 | 1 << PG_swapcache | 1 << PG_active | \
-	 1 << PG_unevictable | __PG_MLOCKED | \
-	 __PG_COMPOUND_LOCK)
+	 1 << PG_unevictable | __PG_MLOCKED)
 
 /*
  * Flags checked when a page is prepped for return by the page allocator.
diff --git a/mm/debug.c b/mm/debug.c
index 668aa35191ca..afe95cf61456 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -40,9 +40,6 @@ static const struct trace_print_flags pageflag_names[] = {
 #ifdef CONFIG_MEMORY_FAILURE
 	{1UL << PG_hwpoison,		"hwpoison"	},
 #endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	{1UL << PG_compound_lock,	"compound_lock"	},
-#endif
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
 	{1UL << PG_young,		"young"		},
 	{1UL << PG_idle,		"idle"		},
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8d7392fac80e..f0efdf89b495 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2463,9 +2463,7 @@ struct mem_cgroup *__mem_cgroup_from_kmem(void *ptr)
 
 /*
  * Because tail pages are not marked as "used", set it. We're under
- * zone->lru_lock, 'splitting on pmd' and compound_lock.
- * charge/uncharge will be never happen and move_account() is done under
- * compound_lock(), so we don't have to take care of races.
+ * zone->lru_lock and migration entries setup in all page mappings.
  */
 void mem_cgroup_split_huge_fixup(struct page *head)
 {
@@ -4548,9 +4546,7 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
  * @from: mem_cgroup which the page is moved from.
  * @to:	mem_cgroup which the page is moved to. @from != @to.
  *
- * The caller must confirm following.
- * - page is not on LRU (isolate_page() is useful.)
- * - compound_lock is held when nr_pages > 1
+ * The caller must make sure the page is not on LRU (isolate_page() is useful.)
  *
  * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
  * from old cgroup.
@@ -4893,8 +4889,7 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
 	struct page *page;
 
 	/*
-	 * We don't take compound_lock() here but no race with splitting thp
-	 * happens because:
+	 * No race with splitting thp happens because:
 	 *  - if pmd_trans_huge_lock() returns 1, the relevant thp is not
 	 *    under splitting, which means there's no concurrent thp split,
 	 *  - if another thread runs into split_huge_page() just after we
-- 
2.5.0

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#1218375 — [PATCHv10 24/36] x86, thp: remove infrastructure for handling splitting PMDs

With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 arch/x86/include/asm/pgtable.h       |  9 ---------
 arch/x86/include/asm/pgtable_types.h |  2 --
 arch/x86/mm/gup.c                    | 13 +------------
 arch/x86/mm/pgtable.c                | 14 --------------
 4 files changed, 1 insertion(+), 37 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index b964d54300e1..a8fdfe0d7277 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -158,11 +158,6 @@ static inline int pmd_large(pmd_t pte)
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static inline int pmd_trans_splitting(pmd_t pmd)
-{
-	return pmd_val(pmd) & _PAGE_SPLITTING;
-}
-
 static inline int pmd_trans_huge(pmd_t pmd)
 {
 	return pmd_val(pmd) & _PAGE_PSE;
@@ -800,10 +795,6 @@ extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
 				  unsigned long address, pmd_t *pmdp);
 
 
-#define __HAVE_ARCH_PMDP_SPLITTING_FLUSH
-extern void pmdp_splitting_flush(struct vm_area_struct *vma,
-				 unsigned long addr, pmd_t *pmdp);
-
 #define __HAVE_ARCH_PMD_WRITE
 static inline int pmd_write(pmd_t pmd)
 {
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 13f310bfc09a..d173197cfd9e 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -22,7 +22,6 @@
 #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
 #define _PAGE_BIT_SPECIAL	_PAGE_BIT_SOFTW1
 #define _PAGE_BIT_CPA_TEST	_PAGE_BIT_SOFTW1
-#define _PAGE_BIT_SPLITTING	_PAGE_BIT_SOFTW2 /* only valid on a PSE pmd */
 #define _PAGE_BIT_HIDDEN	_PAGE_BIT_SOFTW3 /* hidden by kmemcheck */
 #define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_SOFTW3 /* software dirty tracking */
 #define _PAGE_BIT_NX           63       /* No execute: only valid after cpuid check */
@@ -46,7 +45,6 @@
 #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
 #define _PAGE_SPECIAL	(_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL)
 #define _PAGE_CPA_TEST	(_AT(pteval_t, 1) << _PAGE_BIT_CPA_TEST)
-#define _PAGE_SPLITTING	(_AT(pteval_t, 1) << _PAGE_BIT_SPLITTING)
 #define __HAVE_ARCH_PTE_SPECIAL
 
 #ifdef CONFIG_KMEMCHECK
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 62a887a3cf50..49bbbc57603b 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -157,18 +157,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 		pmd_t pmd = *pmdp;
 
 		next = pmd_addr_end(addr, end);
-		/*
-		 * The pmd_trans_splitting() check below explains why
-		 * pmdp_splitting_flush has to flush the tlb, to stop
-		 * this gup-fast code from running while we set the
-		 * splitting bit in the pmd. Returning zero will take
-		 * the slow path that will call wait_split_huge_page()
-		 * if the pmd is still in splitting state. gup-fast
-		 * can't because it has irq disabled and
-		 * wait_split_huge_page() would never return as the
-		 * tlb flush IPI wouldn't run.
-		 */
-		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
+		if (pmd_none(pmd))
 			return 0;
 		if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
 			/*
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index fb0a9dd1d6e4..f52caf9c519b 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -509,20 +509,6 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 
 	return young;
 }
-
-void pmdp_splitting_flush(struct vm_area_struct *vma,
-			  unsigned long address, pmd_t *pmdp)
-{
-	int set;
-	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
-	set = !test_and_set_bit(_PAGE_BIT_SPLITTING,
-				(unsigned long *)pmdp);
-	if (set) {
-		pmd_update(vma->vm_mm, address, pmdp);
-		/* need tlb flush only to serialize against gup-fast */
-		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
-	}
-}
 #endif
 
 /**
-- 
2.5.0

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#1218376 — [PATCHv10 22/36] sparc, thp: remove infrastructure for handling splitting PMDs

With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/sparc/include/asm/pgtable_64.h | 16 ----------------
 arch/sparc/mm/fault_64.c            |  3 ---
 arch/sparc/mm/gup.c                 |  2 +-
 3 files changed, 1 insertion(+), 20 deletions(-)

diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 5833dc5ee7d7..7a38d6a576c5 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -681,13 +681,6 @@ static inline unsigned long pmd_trans_huge(pmd_t pmd)
 	return pte_val(pte) & _PAGE_PMD_HUGE;
 }
 
-static inline unsigned long pmd_trans_splitting(pmd_t pmd)
-{
-	pte_t pte = __pte(pmd_val(pmd));
-
-	return pmd_trans_huge(pmd) && pte_special(pte);
-}
-
 #define has_transparent_hugepage() 1
 
 static inline pmd_t pmd_mkold(pmd_t pmd)
@@ -744,15 +737,6 @@ static inline pmd_t pmd_mkwrite(pmd_t pmd)
 	return __pmd(pte_val(pte));
 }
 
-static inline pmd_t pmd_mksplitting(pmd_t pmd)
-{
-	pte_t pte = __pte(pmd_val(pmd));
-
-	pte = pte_mkspecial(pte);
-
-	return __pmd(pte_val(pte));
-}
-
 static inline pgprot_t pmd_pgprot(pmd_t entry)
 {
 	unsigned long val = pmd_val(entry);
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index dbabe5713a15..cb841a33da59 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -113,9 +113,6 @@ static unsigned int get_user_insn(unsigned long tpc)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (pmd_trans_huge(*pmdp)) {
-		if (pmd_trans_splitting(*pmdp))
-			goto out_irq_enable;
-
 		pa  = pmd_pfn(*pmdp) << PAGE_SHIFT;
 		pa += tpc & ~HPAGE_MASK;
 
diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index 9091c5daa2e1..eb3d8e8ebc6b 100644
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -114,7 +114,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 		pmd_t pmd = *pmdp;
 
 		next = pmd_addr_end(addr, end);
-		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
+		if (pmd_none(pmd))
 			return 0;
 		if (unlikely(pmd_large(pmd))) {
 			if (!gup_huge_pmd(pmdp, pmd, addr, next,
-- 
2.5.0

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