linux-kernel - [PATCH 2/2] mm: mmap: map MAP_STACK to VM

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Date: Wed, 20 Dec 2023 22:59:43 -0800
From: Yang Shi <shy828301@...il.com>
To: oliver.sang@...el.com,
	riel@...riel.com,
	fengwei.yin@...el.com,
	willy@...radead.org,
	cl@...ux.com,
	ying.huang@...el.com,
	akpm@...ux-foundation.org
Cc: shy828301@...il.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH 2/2] mm: mmap: map MAP_STACK to VM_NOHUGEPAGE

From: Yang Shi <yang@...amperecomputing.com>

The 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/

Reported-by: kernel test robot <oliver.sang@...el.com>
Tested-by: Oliver Sang <oliver.sang@...el.com>
Cc: Yin Fengwei <fengwei.yin@...el.com>
Cc: Rik van Riel <riel@...riel.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Christopher Lameter <cl@...ux.com>
Cc: Huang, Ying <ying.huang@...el.com>
Signed-off-by: Yang Shi <yang@...amperecomputing.com>
---
 include/linux/mman.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index 40d94411d492..dc7048824be8 100644
--- a/include/linux/mman.h
+++ b/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);
 }
 
-- 
2.41.0