linux-stable.git/mm/memory.c, branch v4.1.2

mm: new pfn_mkwrite same as page_mkwrite for VM_PFNMAP

2015-04-15T23:35:20+00:00

This will allow FS that uses VM_PFNMAP | VM_MIXEDMAP (no page structs) to
get notified when access is a write to a read-only PFN.

This can happen if we mmap() a file then first mmap-read from it to
page-in a read-only PFN, than we mmap-write to the same page.

We need this functionality to fix a DAX bug, where in the scenario above
we fail to set ctime/mtime though we modified the file.  An xfstest is
attached to this patchset that shows the failure and the fix.  (A DAX
patch will follow)

This functionality is extra important for us, because upon dirtying of a
pmem page we also want to RDMA the page to a remote cluster node.

We define a new pfn_mkwrite and do not reuse page_mkwrite because
  1 - The name ;-)
  2 - But mainly because it would take a very long and tedious
      audit of all page_mkwrite functions of VM_MIXEDMAP/VM_PFNMAP
      users. To make sure they do not now CRASH. For example current
      DAX code (which this is for) would crash.
      If we would want to reuse page_mkwrite, We will need to first
      patch all users, so to not-crash-on-no-page. Then enable this
      patch. But even if I did that I would not sleep so well at night.
      Adding a new vector is the safest thing to do, and is not that
      expensive. an extra pointer at a static function vector per driver.
      Also the new vector is better for performance, because else we
      Will call all current Kernel vectors, so to:
        check-ha-no-page-do-nothing and return.

No need to call it from do_shared_fault because do_wp_page is called to
change pte permissions anyway.

Signed-off-by: Yigal Korman 
Signed-off-by: Boaz Harrosh 
Acked-by: Kirill A. Shutemov 
Cc: Matthew Wilcox 
Cc: Jan Kara 
Cc: Hugh Dickins 
Cc: Mel Gorman 
Cc: Dave Chinner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/memory: also print a_ops->readpage in print_bad_pte()

2015-04-15T23:35:20+00:00

A lot of filesystems use generic_file_mmap() and filemap_fault(),
f_op->mmap and vm_ops->fault aren't enough to identify filesystem.

This prints file name, vm_ops->fault, f_op->mmap and a_ops->readpage
(which is almost always implemented and filesystem-specific).

Example:

[   23.676410] BUG: Bad page map in process sh  pte:1b7e6025 pmd:19bbd067
[   23.676887] page:ffffea00006df980 count:4 mapcount:1 mapping:ffff8800196426c0 index:0x97
[   23.677481] flags: 0x10000000000000c(referenced|uptodate)
[   23.677896] page dumped because: bad pte
[   23.678205] addr:00007f52fcb17000 vm_flags:00000075 anon_vma:          (null) mapping:ffff8800196426c0 index:97
[   23.678922] file:libc-2.19.so fault:filemap_fault mmap:generic_file_readonly_mmap readpage:v9fs_vfs_readpage

[akpm@linux-foundation.org: use pr_alert, per Kirill]
Signed-off-by: Konstantin Khlebnikov 
Cc: Sasha Levin 
Acked-by: Kirill A. Shutemov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: remove rest of ACCESS_ONCE() usages

2015-04-15T23:35:18+00:00

We converted some of the usages of ACCESS_ONCE to READ_ONCE in the mm/
tree since it doesn't work reliably on non-scalar types.

This patch removes the rest of the usages of ACCESS_ONCE, and use the new
READ_ONCE API for the read accesses.  This makes things cleaner, instead
of using separate/multiple sets of APIs.

Signed-off-by: Jason Low 
Acked-by: Michal Hocko 
Acked-by: Davidlohr Bueso 
Acked-by: Rik van Riel 
Reviewed-by: Christian Borntraeger 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: refactor do_wp_page handling of shared vma into a function

2015-04-14T23:49:03+00:00

The do_wp_page function is extremely long.  Extract the logic for
handling a page belonging to a shared vma into a function of its own.

This helps the readability of the code, without doing any functional
change in it.

Signed-off-by: Shachar Raindel 
Acked-by: Linus Torvalds 
Acked-by: Kirill A. Shutemov 
Acked-by: Rik van Riel 
Acked-by: Andi Kleen 
Acked-by: Haggai Eran 
Acked-by: Johannes Weiner 
Cc: Mel Gorman 
Cc: Matthew Wilcox 
Cc: Dave Hansen 
Cc: Naoya Horiguchi 
Cc: Andrea Arcangeli 
Cc: Peter Feiner 
Cc: Michel Lespinasse 
Reviewed-by: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: refactor do_wp_page, extract the page copy flow

2015-04-14T23:49:03+00:00

In some cases, do_wp_page had to copy the page suffering a write fault
to a new location.  If the function logic decided that to do this, it
was done by jumping with a "goto" operation to the relevant code block.
This made the code really hard to understand.  It is also against the
kernel coding style guidelines.

This patch extracts the page copy and page table update logic to a
separate function.  It also clean up the naming, from "gotten" to
"wp_page_copy", and adds few comments.

Signed-off-by: Shachar Raindel 
Acked-by: Linus Torvalds 
Acked-by: Kirill A. Shutemov 
Acked-by: Rik van Riel 
Acked-by: Andi Kleen 
Acked-by: Haggai Eran 
Acked-by: Johannes Weiner 
Cc: Mel Gorman 
Cc: Matthew Wilcox 
Cc: Dave Hansen 
Cc: Naoya Horiguchi 
Cc: Andrea Arcangeli 
Cc: Peter Feiner 
Cc: Michel Lespinasse 
Reviewed-by: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: refactor do_wp_page - rewrite the unlock flow

2015-04-14T23:49:03+00:00

When do_wp_page is ending, in several cases it needs to unlock the pages
and ptls it was accessing.

Currently, this logic was "called" by using a goto jump.  This makes
following the control flow of the function harder.  Readability was
further hampered by the unlock case containing large amount of logic
needed only in one of the 3 cases.

Using goto for cleanup is generally allowed.  However, moving the
trivial unlocking flows to the relevant call sites allow deeper
refactoring in the next patch.

Signed-off-by: Shachar Raindel 
Acked-by: Linus Torvalds 
Acked-by: Kirill A. Shutemov 
Acked-by: Rik van Riel 
Acked-by: Andi Kleen 
Acked-by: Haggai Eran 
Acked-by: Johannes Weiner 
Cc: Mel Gorman 
Cc: Matthew Wilcox 
Cc: Dave Hansen 
Cc: Naoya Horiguchi 
Cc: Andrea Arcangeli 
Cc: Peter Feiner 
Cc: Michel Lespinasse 
Reviewed-by: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: refactor do_wp_page, extract the reuse case

2015-04-14T23:49:03+00:00

Currently do_wp_page contains 265 code lines.  It also contains 9 goto
statements, of which 5 are targeting labels which are not cleanup
related.  This makes the function extremely difficult to understand.

The following patches are an attempt at breaking the function to its
basic components, and making it easier to understand.

The patches are straight forward function extractions from do_wp_page.
As we extract functions, we remove unneeded parameters and simplify the
code as much as possible.  However, the functionality is supposed to
remain completely unchanged.  The patches also attempt to document the
functionality of each extracted function.  In patch 2, we split the
unlock logic to the contain logic relevant to specific needs of each use
case, instead of having huge number of conditional decisions in a single
unlock flow.

This patch (of 4):

When do_wp_page is ending, in several cases it needs to reuse the existing
page.  This is achieved by making the page table writable, and possibly
updating the page-cache state.

Currently, this logic was "called" by using a goto jump.  This makes
following the control flow of the function harder.  It is also against the
coding style guidelines for using goto.

As the code can easily be refactored into a specialized function, refactor
it out and simplify the code flow in do_wp_page.

Acked-by: Linus Torvalds 
Acked-by: Kirill A. Shutemov 
Acked-by: Rik van Riel 
Acked-by: Andi Kleen 
Acked-by: Haggai Eran 
Acked-by: Johannes Weiner 
Cc: Mel Gorman 
Cc: Matthew Wilcox 
Cc: Dave Hansen 
Cc: Naoya Horiguchi 
Cc: Andrea Arcangeli 
Cc: Peter Feiner 
Cc: Michel Lespinasse 
Reviewed-by: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: numa: slow PTE scan rate if migration failures occur

2015-03-25T23:20:31+00:00

Dave Chinner reported the following on https://lkml.org/lkml/2015/3/1/226

  Across the board the 4.0-rc1 numbers are much slower, and the degradation
  is far worse when using the large memory footprint configs. Perf points
  straight at the cause - this is from 4.0-rc1 on the "-o bhash=101073" config:

   -   56.07%    56.07%  [kernel]            [k] default_send_IPI_mask_sequence_phys
      - default_send_IPI_mask_sequence_phys
         - 99.99% physflat_send_IPI_mask
            - 99.37% native_send_call_func_ipi
                 smp_call_function_many
               - native_flush_tlb_others
                  - 99.85% flush_tlb_page
                       ptep_clear_flush
                       try_to_unmap_one
                       rmap_walk
                       try_to_unmap
                       migrate_pages
                       migrate_misplaced_page
                     - handle_mm_fault
                        - 99.73% __do_page_fault
                             trace_do_page_fault
                             do_async_page_fault
                           + async_page_fault
              0.63% native_send_call_func_single_ipi
                 generic_exec_single
                 smp_call_function_single

This is showing excessive migration activity even though excessive
migrations are meant to get throttled.  Normally, the scan rate is tuned
on a per-task basis depending on the locality of faults.  However, if
migrations fail for any reason then the PTE scanner may scan faster if
the faults continue to be remote.  This means there is higher system CPU
overhead and fault trapping at exactly the time we know that migrations
cannot happen.  This patch tracks when migration failures occur and
slows the PTE scanner.

Signed-off-by: Mel Gorman 
Reported-by: Dave Chinner 
Tested-by: Dave Chinner 
Cc: Ingo Molnar 
Cc: Aneesh Kumar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: numa: preserve PTE write permissions across a NUMA hinting fault

2015-03-25T23:20:31+00:00

Protecting a PTE to trap a NUMA hinting fault clears the writable bit
and further faults are needed after trapping a NUMA hinting fault to set
the writable bit again.  This patch preserves the writable bit when
trapping NUMA hinting faults.  The impact is obvious from the number of
minor faults trapped during the basis balancing benchmark and the system
CPU usage;

  autonumabench
                                             4.0.0-rc4             4.0.0-rc4
                                              baseline              preserve
  Time System-NUMA01                  107.13 (  0.00%)      103.13 (  3.73%)
  Time System-NUMA01_THEADLOCAL       131.87 (  0.00%)       83.30 ( 36.83%)
  Time System-NUMA02                    8.95 (  0.00%)       10.72 (-19.78%)
  Time System-NUMA02_SMT                4.57 (  0.00%)        3.99 ( 12.69%)
  Time Elapsed-NUMA01                 515.78 (  0.00%)      517.26 ( -0.29%)
  Time Elapsed-NUMA01_THEADLOCAL      384.10 (  0.00%)      384.31 ( -0.05%)
  Time Elapsed-NUMA02                  48.86 (  0.00%)       48.78 (  0.16%)
  Time Elapsed-NUMA02_SMT              47.98 (  0.00%)       48.12 ( -0.29%)

               4.0.0-rc4   4.0.0-rc4
                baseline    preserve
  User          44383.95    43971.89
  System          252.61      201.24
  Elapsed         998.68     1000.94

  Minor Faults   2597249     1981230
  Major Faults       365         364

There is a similar drop in system CPU usage using Dave Chinner's xfsrepair
workload

                                      4.0.0-rc4             4.0.0-rc4
                                       baseline              preserve
  Amean    real-xfsrepair      454.14 (  0.00%)      442.36 (  2.60%)
  Amean    syst-xfsrepair      277.20 (  0.00%)      204.68 ( 26.16%)

The patch looks hacky but the alternatives looked worse.  The tidest was
to rewalk the page tables after a hinting fault but it was more complex
than this approach and the performance was worse.  It's not generally
safe to just mark the page writable during the fault if it's a write
fault as it may have been read-only for COW so that approach was
discarded.

Signed-off-by: Mel Gorman 
Reported-by: Dave Chinner 
Tested-by: Dave Chinner 
Cc: Ingo Molnar 
Cc: Aneesh Kumar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: numa: group related processes based on VMA flags instead of page table flags

2015-03-25T23:20:31+00:00

These are three follow-on patches based on the xfsrepair workload Dave
Chinner reported was problematic in 4.0-rc1 due to changes in page table
management -- https://lkml.org/lkml/2015/3/1/226.

Much of the problem was reduced by commit 53da3bc2ba9e ("mm: fix up numa
read-only thread grouping logic") and commit ba68bc0115eb ("mm: thp:
Return the correct value for change_huge_pmd").  It was known that the
performance in 3.19 was still better even if is far less safe.  This
series aims to restore the performance without compromising on safety.

For the test of this mail, I'm comparing 3.19 against 4.0-rc4 and the
three patches applied on top

  autonumabench
                                                3.19.0             4.0.0-rc4             4.0.0-rc4             4.0.0-rc4             4.0.0-rc4
                                               vanilla               vanilla          vmwrite-v5r8         preserve-v5r8         slowscan-v5r8
  Time System-NUMA01                  124.00 (  0.00%)      161.86 (-30.53%)      107.13 ( 13.60%)      103.13 ( 16.83%)      145.01 (-16.94%)
  Time System-NUMA01_THEADLOCAL       115.54 (  0.00%)      107.64 (  6.84%)      131.87 (-14.13%)       83.30 ( 27.90%)       92.35 ( 20.07%)
  Time System-NUMA02                    9.35 (  0.00%)       10.44 (-11.66%)        8.95 (  4.28%)       10.72 (-14.65%)        8.16 ( 12.73%)
  Time System-NUMA02_SMT                3.87 (  0.00%)        4.63 (-19.64%)        4.57 (-18.09%)        3.99 ( -3.10%)        3.36 ( 13.18%)
  Time Elapsed-NUMA01                 570.06 (  0.00%)      567.82 (  0.39%)      515.78 (  9.52%)      517.26 (  9.26%)      543.80 (  4.61%)
  Time Elapsed-NUMA01_THEADLOCAL      393.69 (  0.00%)      384.83 (  2.25%)      384.10 (  2.44%)      384.31 (  2.38%)      380.73 (  3.29%)
  Time Elapsed-NUMA02                  49.09 (  0.00%)       49.33 ( -0.49%)       48.86 (  0.47%)       48.78 (  0.63%)       50.94 ( -3.77%)
  Time Elapsed-NUMA02_SMT              47.51 (  0.00%)       47.15 (  0.76%)       47.98 ( -0.99%)       48.12 ( -1.28%)       49.56 ( -4.31%)

                3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
               vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
  User        46334.60    46391.94    44383.95    43971.89    44372.12
  System        252.84      284.66      252.61      201.24      249.00
  Elapsed      1062.14     1050.96      998.68     1000.94     1026.78

Overall the system CPU usage is comparable and the test is naturally a
bit variable.  The slowing of the scanner hurts numa01 but on this
machine it is an adverse workload and patches that dramatically help it
often hurt absolutely everything else.

Due to patch 2, the fault activity is interesting

                                  3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
                                 vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
  Minor Faults                   2097811     2656646     2597249     1981230     1636841
  Major Faults                       362         450         365         364         365

Note the impact preserving the write bit across protection updates and
fault reduces faults.

  NUMA alloc hit                 1229008     1217015     1191660     1178322     1199681
  NUMA alloc miss                      0           0           0           0           0
  NUMA interleave hit                  0           0           0           0           0
  NUMA alloc local               1228514     1216317     1190871     1177448     1199021
  NUMA base PTE updates        245706197   240041607   238195516   244704842   115012800
  NUMA huge PMD updates           479530      468448      464868      477573      224487
  NUMA page range updates      491225557   479886983   476207932   489222218   229950144
  NUMA hint faults                659753      656503      641678      656926      294842
  NUMA hint local faults          381604      373963      360478      337585      186249
  NUMA hint local percent             57          56          56          51          63
  NUMA pages migrated            5412140     6374899     6266530     5277468     5755096
  AutoNUMA cost                    5121%       5083%       4994%       5097%       2388%

Here the impact of slowing the PTE scanner on migratrion failures is
obvious as "NUMA base PTE updates" and "NUMA huge PMD updates" are
massively reduced even though the headline performance is very similar.

As xfsrepair was the reported workload here is the impact of the series
on it.

  xfsrepair
                                         3.19.0             4.0.0-rc4             4.0.0-rc4             4.0.0-rc4             4.0.0-rc4
                                        vanilla               vanilla          vmwrite-v5r8         preserve-v5r8         slowscan-v5r8
  Min      real-fsmark        1183.29 (  0.00%)     1165.73 (  1.48%)     1152.78 (  2.58%)     1153.64 (  2.51%)     1177.62 (  0.48%)
  Min      syst-fsmark        4107.85 (  0.00%)     4027.75 (  1.95%)     3986.74 (  2.95%)     3979.16 (  3.13%)     4048.76 (  1.44%)
  Min      real-xfsrepair      441.51 (  0.00%)      463.96 ( -5.08%)      449.50 ( -1.81%)      440.08 (  0.32%)      439.87 (  0.37%)
  Min      syst-xfsrepair      195.76 (  0.00%)      278.47 (-42.25%)      262.34 (-34.01%)      203.70 ( -4.06%)      143.64 ( 26.62%)
  Amean    real-fsmark        1188.30 (  0.00%)     1177.34 (  0.92%)     1157.97 (  2.55%)     1158.21 (  2.53%)     1182.22 (  0.51%)
  Amean    syst-fsmark        4111.37 (  0.00%)     4055.70 (  1.35%)     3987.19 (  3.02%)     3998.72 (  2.74%)     4061.69 (  1.21%)
  Amean    real-xfsrepair      450.88 (  0.00%)      468.32 ( -3.87%)      454.14 ( -0.72%)      442.36 (  1.89%)      440.59 (  2.28%)
  Amean    syst-xfsrepair      199.66 (  0.00%)      290.60 (-45.55%)      277.20 (-38.84%)      204.68 ( -2.51%)      150.55 ( 24.60%)
  Stddev   real-fsmark           4.12 (  0.00%)       10.82 (-162.29%)       4.14 ( -0.28%)        5.98 (-45.05%)        4.60 (-11.53%)
  Stddev   syst-fsmark           2.63 (  0.00%)       20.32 (-671.82%)       0.37 ( 85.89%)       16.47 (-525.59%)      15.05 (-471.79%)
  Stddev   real-xfsrepair        6.87 (  0.00%)        4.55 ( 33.75%)        3.46 ( 49.58%)        1.78 ( 74.12%)        0.52 ( 92.50%)
  Stddev   syst-xfsrepair        3.02 (  0.00%)       10.30 (-241.37%)      13.17 (-336.37%)       0.71 ( 76.63%)        5.00 (-65.61%)
  CoeffVar real-fsmark           0.35 (  0.00%)        0.92 (-164.73%)       0.36 ( -2.91%)        0.52 (-48.82%)        0.39 (-12.10%)
  CoeffVar syst-fsmark           0.06 (  0.00%)        0.50 (-682.41%)       0.01 ( 85.45%)        0.41 (-543.22%)       0.37 (-478.78%)
  CoeffVar real-xfsrepair        1.52 (  0.00%)        0.97 ( 36.21%)        0.76 ( 49.94%)        0.40 ( 73.62%)        0.12 ( 92.33%)
  CoeffVar syst-xfsrepair        1.51 (  0.00%)        3.54 (-134.54%)       4.75 (-214.31%)       0.34 ( 77.20%)        3.32 (-119.63%)
  Max      real-fsmark        1193.39 (  0.00%)     1191.77 (  0.14%)     1162.90 (  2.55%)     1166.66 (  2.24%)     1188.50 (  0.41%)
  Max      syst-fsmark        4114.18 (  0.00%)     4075.45 (  0.94%)     3987.65 (  3.08%)     4019.45 (  2.30%)     4082.80 (  0.76%)
  Max      real-xfsrepair      457.80 (  0.00%)      474.60 ( -3.67%)      457.82 ( -0.00%)      444.42 (  2.92%)      441.03 (  3.66%)
  Max      syst-xfsrepair      203.11 (  0.00%)      303.65 (-49.50%)      294.35 (-44.92%)      205.33 ( -1.09%)      155.28 ( 23.55%)

The really relevant lines as syst-xfsrepair which is the system CPU
usage when running xfsrepair.  Note that on my machine the overhead was
45% higher on 4.0-rc4 which may be part of what Dave is seeing.  Once we
preserve the write bit across faults, it's only 2.51% higher on average.
With the full series applied, system CPU usage is 24.6% lower on
average.

Again, the impact of preserving the write bit on minor faults is obvious
and the impact of slowing scanning after migration failures is obvious
on the PTE updates.  Note also that the number of pages migrated is much
reduced even though the headline performance is comparable.

                                  3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
                                 vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
  Minor Faults                 153466827   254507978   249163829   153501373   105737890
  Major Faults                       610         702         690         649         724
  NUMA base PTE updates        217735049   210756527   217729596   216937111   144344993
  NUMA huge PMD updates           129294       85044      106921      127246       79887
  NUMA pages migrated           21938995    29705270    28594162    22687324    16258075

                        3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
                       vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
  Mean sdb-avgqusz       13.47        2.54        2.55        2.47        2.49
  Mean sdb-avgrqsz      202.32      140.22      139.50      139.02      138.12
  Mean sdb-await         25.92        5.09        5.33        5.02        5.22
  Mean sdb-r_await        4.71        0.19        0.83        0.51        0.11
  Mean sdb-w_await      104.13        5.21        5.38        5.05        5.32
  Mean sdb-svctm          0.59        0.13        0.14        0.13        0.14
  Mean sdb-rrqm           0.16        0.00        0.00        0.00        0.00
  Mean sdb-wrqm           3.59     1799.43     1826.84     1812.21     1785.67
  Max  sdb-avgqusz      111.06       12.13       14.05       11.66       15.60
  Max  sdb-avgrqsz      255.60      190.34      190.01      187.33      191.78
  Max  sdb-await        168.24       39.28       49.22       44.64       65.62
  Max  sdb-r_await      660.00       52.00      280.00       76.00       12.00
  Max  sdb-w_await     7804.00       39.28       49.22       44.64       65.62
  Max  sdb-svctm          4.00        2.82        2.86        1.98        2.84
  Max  sdb-rrqm           8.30        0.00        0.00        0.00        0.00
  Max  sdb-wrqm          34.20     5372.80     5278.60     5386.60     5546.15

FWIW, I also checked SPECjbb in different configurations but it's
similar observations -- minor faults lower, PTE update activity lower
and performance is roughly comparable against 3.19.

This patch (of 3):

Threads that share writable data within pages are grouped together as
related tasks.  This decision is based on whether the PTE is marked
dirty which is subject to timing races between the PTE scanner update
and when the application writes the page.  If the page is file-backed,
then background flushes and sync also affect placement.  This is
unpredictable behaviour which is impossible to reason about so this
patch makes grouping decisions based on the VMA flags.

Signed-off-by: Mel Gorman 
Reported-by: Dave Chinner 
Tested-by: Dave Chinner 
Cc: Ingo Molnar 
Cc: Aneesh Kumar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds