Re: [PATCH 2/2] mm: mmap: map MAP_STACK to VM_NOHUGEPAGE

[Yin Fengwei <fengwei.yin@intel.com>]

On 2023/12/21 14:59, Yang Shi wrote:
> From: Yang Shi <yang@os.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@intel.com>
> Tested-by: Oliver Sang <oliver.sang@intel.com>
> Cc: 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: Yang Shi <yang@os.amperecomputing.com>

Reviewed-by: Yin Fengwei <fengwei.yin@intel.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);
>   }
>