• Alex Thorlton's avatar
    mm: revert "thp: make MADV_HUGEPAGE check for mm->def_flags" · 1e1836e8
    Alex Thorlton authored
    The main motivation behind this patch is to provide a way to disable THP
    for jobs where the code cannot be modified, and using a malloc hook with
    madvise is not an option (i.e.  statically allocated data).  This patch
    allows us to do just that, without affecting other jobs running on the
    We need to do this sort of thing for jobs where THP hurts performance,
    due to the possibility of increased remote memory accesses that can be
    created by situations such as the following:
    When you touch 1 byte of an untouched, contiguous 2MB chunk, a THP will
    be handed out, and the THP will be stuck on whatever node the chunk was
    originally referenced from.  If many remote nodes need to do work on
    that same chunk, they'll be making remote accesses.
    With THP disabled, 4K pages can be handed out to separate nodes as
    they're needed, greatly reducing the amount of remote accesses to
    This patch is based on some of my work combined with some
    suggestions/patches given by Oleg Nesterov.  The main goal here is to
    add a prctl switch to allow us to disable to THP on a per mm_struct
    Here's a bit of test data with the new patch in place...
    First with the flag unset:
      # perf stat -a ./prctl_wrapper_mmv3 0 ./thp_pthread -C 0 -m 0 -c 512 -b 256g
      Setting thp_disabled for this task...
      thp_disable: 0
      Set thp_disabled state to 0
      Process pid = 18027
                                      MAX        MIN                                  TOTCPU/      TOT_PF/   TOT_PF/     WSEC/
      TYPE:               CPUS       WALL       WALL        SYS     USER     TOTCPU       CPU     WALL_SEC   SYS_SEC       CPU   NODES
       512      1.120      0.060      0.000    0.110      0.110     0.000    28571428864 -9223372036854775808  55803572      23
       Performance counter stats for './prctl_wrapper_mmv3_hack 0 ./thp_pthread -C 0 -m 0 -c 512 -b 256g':
        273719072.841402 task-clock                #  641.026 CPUs utilized           [100.00%]
               1,008,986 context-switches          #    0.000 M/sec                   [100.00%]
                   7,717 CPU-migrations            #    0.000 M/sec                   [100.00%]
               1,698,932 page-faults               #    0.000 M/sec
      355,222,544,890,379 cycles                   #    1.298 GHz                     [100.00%]
      536,445,412,234,588 stalled-cycles-frontend  #  151.02% frontend cycles idle    [100.00%]
      409,110,531,310,223 stalled-cycles-backend   #  115.17% backend  cycles idle    [100.00%]
      148,286,797,266,411 instructions             #    0.42  insns per cycle
                                                   #    3.62  stalled cycles per insn [100.00%]
      27,061,793,159,503 branches                  #   98.867 M/sec                   [100.00%]
           1,188,655,196 branch-misses             #    0.00% of all branches
           427.001706337 seconds time elapsed
    Now with the flag set:
      # perf stat -a ./prctl_wrapper_mmv3 1 ./thp_pthread -C 0 -m 0 -c 512 -b 256g
      Setting thp_disabled for this task...
      thp_disable: 1
      Set thp_disabled state to 1
      Process pid = 144957
                                      MAX        MIN                                  TOTCPU/      TOT_PF/   TOT_PF/     WSEC/
      TYPE:               CPUS       WALL       WALL        SYS     USER     TOTCPU       CPU     WALL_SEC   SYS_SEC       CPU   NODES
       512      0.620      0.260      0.250    0.320      0.570     0.001    51612901376 128000000000 100806448      23
       Performance counter stats for './prctl_wrapper_mmv3_hack 1 ./thp_pthread -C 0 -m 0 -c 512 -b 256g':
        138789390.540183 task-clock                #  641.959 CPUs utilized           [100.00%]
                 534,205 context-switches          #    0.000 M/sec                   [100.00%]
                   4,595 CPU-migrations            #    0.000 M/sec                   [100.00%]
              63,133,119 page-faults               #    0.000 M/sec
      147,977,747,269,768 cycles                   #    1.066 GHz                     [100.00%]
      200,524,196,493,108 stalled-cycles-frontend  #  135.51% frontend cycles idle    [100.00%]
      105,175,163,716,388 stalled-cycles-backend   #   71.07% backend  cycles idle    [100.00%]
      180,916,213,503,160 instructions             #    1.22  insns per cycle
                                                   #    1.11  stalled cycles per insn [100.00%]
      26,999,511,005,868 branches                  #  194.536 M/sec                   [100.00%]
             714,066,351 branch-misses             #    0.00% of all branches
           216.196778807 seconds time elapsed
    As with previous versions of the patch, We're getting about a 2x
    performance increase here.  Here's a link to the test case I used, along
    with the little wrapper to activate the flag:
    This patch (of 3):
    Revert commit 8e72033f and add in code to fix up any issues caused
    by the revert.
    The revert is necessary because hugepage_madvise would return -EINVAL
    when VM_NOHUGEPAGE is set, which will break subsequent chunks of this
    patch set.
    Here's a snip of an e-mail from Gerald detailing the original purpose of
    this code, and providing justification for the revert:
      "The intent of commit 8e72033f was to guard against any future
       programming errors that may result in an madvice(MADV_HUGEPAGE) on
       guest mappings, which would crash the kernel.
       Martin suggested adding the bit to arch/s390/mm/pgtable.c, if
       8e72033f was to be reverted, because that check will also prevent
       a kernel crash in the case described above, it will now send a
       SIGSEGV instead.
       This would now also allow to do the madvise on other parts, if
       needed, so it is a more flexible approach.  One could also say that
       it would have been better to do it this way right from the
    Signed-off-by: default avatarAlex Thorlton <athorlton@sgi.com>
    Suggested-by: default avatarOleg Nesterov <oleg@redhat.com>
    Tested-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
    Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
huge_memory.c 76 KB