Thanks Yang,
Should this be marked for stable? Given how easily it is for pthreads
to allocate hugepages w/o this change, it can easily cause memory
bloat on larger systems and/or users with high thread counts. I don't
think that will be welcomed, and seems odd that just 6.7 should suffer
this.
Thanks,
Zach
On Tue, Jan 9, 2024 at 5:36 PM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote:
>
>
>
> On 2023/12/21 14:59, Yang Shi wrote:
> > From: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxx/
> >
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Tested-by: Oliver Sang <oliver.sang@xxxxxxxxx>
> > Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> > Cc: Rik van Riel <riel@xxxxxxxxxxx>
> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Cc: Christopher Lameter <cl@xxxxxxxxx>
> > Cc: Huang, Ying <ying.huang@xxxxxxxxx>
> > Signed-off-by: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
>
> Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>
> > ---
> > 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);
> > }
> >
>
