+ mm-mmap-map-map_stack-to-vm_nohugepage.patch added to mm-unstable branch

+ mm-mmap-map-map_stack-to-vm_nohugepage.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: mmap: map MAP_STACK to VM_NOHUGEPAGE
has been added to the -mm mm-unstable branch.  Its filename is
     mm-mmap-map-map_stack-to-vm_nohugepage.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-map-map_stack-to-vm_nohugepage.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Yang Shi <yang@os.amperecomputing.com>
Subject: mm: mmap: map MAP_STACK to VM_NOHUGEPAGE
Date: Wed, 20 Dec 2023 22:59:43 -0800

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/202312192310.56367035-oliver.sang@intel.com/

Link: https://lkml.kernel.org/r/20231221065943.2803551-2-shy828301@gmail.com
Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Tested-by: Oliver Sang <oliver.sang@intel.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christopher Lameter <cl@linux.com>
Cc: Huang, Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mman.h |    1 +
 1 file changed, 1 insertion(+)

--- a/include/linux/mman.h~mm-mmap-map-map_stack-to-vm_nohugepage
+++ a/include/linux/mman.h
@@ -156,6 +156,7 @@ calc_vm_flag_bits(unsigned long flags)
 	return _calc_vm_trans(flags, MAP_GROWSDOWN,  VM_GROWSDOWN ) |
 	       _calc_vm_trans(flags, MAP_LOCKED,     VM_LOCKED    ) |
 	       _calc_vm_trans(flags, MAP_SYNC,	     VM_SYNC      ) |
+	       _calc_vm_trans(flags, MAP_STACK,	     VM_NOHUGEPAGE) |
 	       arch_calc_vm_flag_bits(flags);
 }
 
_

Patches currently in -mm which might be from yang@os.amperecomputing.com are

mm-mmap-no-need-to-call-khugepaged_enter_vma-for-stack.patch
mm-mmap-map-map_stack-to-vm_nohugepage.patch