mm: mmap: map MAP_STACK to VM_NOHUGEPAGE

commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
boundaries") incured regression for stress-ng pthread benchmark [1].  It
is because THP get allocated to pthread's stack area much more possible
than before.  Pthread's stack area is allocated by mmap without
VM_GROWSDOWN or VM_GROWSUP flag, so kernel can't tell whether it is a
stack area or not.

The MAP_STACK flag is used to mark the stack area, but it is a no-op on
Linux.  Mapping MAP_STACK to VM_NOHUGEPAGE to prevent from allocating THP
for such stack area.

With this change the stack area looks like:

fffd18e10000-fffd19610000 rw-p 00000000 00:00 0
Size:               8192 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                  12 kB
Pss:                  12 kB
Pss_Dirty:            12 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:        12 kB
Referenced:           12 kB
Anonymous:            12 kB
KSM:                   0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:           0
VmFlags: rd wr mr mw me ac nh

The "nh" flag is set.

[1] https://lore.kernel.org/linux-mm/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries")
Signed-off-by: Yang Shi <[email protected]>
Reported-by: kernel test robot <[email protected]>
Tested-by: Oliver Sang <[email protected]>
Reviewed-by: Yin Fengwei <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Christopher Lameter <[email protected]>
Cc: Huang, Ying <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions