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Stoakes wrote: > +cc Matthew > > On Fri, May 02, 2025 at 01:53:15PM -0700, Yang Shi wrote: >> >> On 5/2/25 5:46 AM, Lorenzo Stoakes wrote: >>> +cc Andrew. >>> >>> Ignacio, you should always include Andrew in patch submissions to mm :) >>> >>> +cc Yang Shi who added this in the first place in commit c4608d1bf7c6 ("mm: >>> mmap: map MAP_STACK to VM_NOHUGEPAGE"). >> Thanks for cc'ing me. > No problem! > >>> On Fri, May 02, 2025 at 11:31:41AM +0200, Ignacio Moreno Gonzalez via B4 Relay wrote: >>>> From: Ignacio Moreno Gonzalez >>>> >>>> commit c4608d1bf7c6 ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE") maps >>>> the mmap option MAP_STACK to VM_NOHUGEPAGE. This is also done if >>>> CONFIG_TRANSPARENT_HUGETABLES is not defined. But in that case, the >>>> VM_NOHUGEPAGE does not make sense. For instance, when calling madvise() >>>> with MADV_NOHUGEPAGE, an error is always returned. >>>> >>>> Signed-off-by: Ignacio Moreno Gonzalez >>> I don't see how can this cause a problem, and it fixes one in practice, so >>> LGTM. Though see note below about CRIU :) >>> >>> I also added a nit below, if you address this you can re-use my tag. >>> >>> Reviewed-by: Lorenzo Stoakes >> Yeah, I agree. Looks good to me too. Reviewed-by: Yang Shi >> > Thanks! > > I also believe Matthew's suggestion (see [0]) is very much worth doing > here, in my view doing both is a sensible approach, would your R-b tag > extend to that? Yes. VM_NOHUGEPAGE is a no-op on !THP kernel anyway. It is pointless to fail it. It should be unlikely any real life application rely on this behavior (returning -EINVAL). > > In which case, Ignacio - could you apply both Matthew's change and address > the nit below and send a v2? > > Thanks! > > [0]: https://lore.kernel.org/linux-mm/aBTCtOXBhUK_FLU6@casper.infradead.org/ > >>> Thanks! >>> >>> Do we want to back port this to stable kernels? If so we should have a: >>> >>> Fixes: c4608d1bf7c6 ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE") >>> cc: stable@vger.kernel.org >>> >>> Appended here, and Greg's scripts should automagically backport, assuming >>> no conflicts or such (I don't _think_ there would be...) >>> >>>> --- >>>> I discovered this issue when trying to use the tool CRIU to checkpoint >>>> and restore a container. Our running kernel is compiled without >>>> CONFIG_TRANSPARENT_HUGETABLES. CRIU parses the output of >>>> /proc//smaps and saves the "nh" flag. When trying to restore the >>>> container, CRIU fails to restore the "nh" mappings, since madvise() >>>> MADV_NOHUGEPAGE always returns an error because >>>> CONFIG_TRANSPARENT_HUGETABLES is not defined. >>> Yeah this is really not a stable or valid use of the /proc/$pid/[s]maps >>> interface :P CRIU is sort of a blurry line of relying on internal >>> implementation details so we're kinda not obligated to prevent breakages. >>> >>> CRIU is kinda relying on internal implementation details so debatable as to >>> whether we should be bending over backwards to support. >>> >>> BUT, we also don't want to cause unwanted issues if there's a simple fix >>> and this seems reasonable to me. >>> >>>> --- >>>> include/linux/mman.h | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/include/linux/mman.h b/include/linux/mman.h >>>> index bce214fece16b9af3791a2baaecd6063d0481938..1e83bc0e3db670b04743f5208826e87455a05325 100644 >>>> --- a/include/linux/mman.h >>>> +++ b/include/linux/mman.h >>>> @@ -155,7 +155,9 @@ calc_vm_flag_bits(struct file *file, 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 ) | >>>> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) >>> NIT, but can we use ifdef here for consistency? Thanks. >>> >>>> _calc_vm_trans(flags, MAP_STACK, VM_NOHUGEPAGE) | >>>> +#endif >>>> arch_calc_vm_flag_bits(file, flags); >>>> } >>>> >>>> >>>> --- >>>> base-commit: fc96b232f8e7c0a6c282f47726b2ff6a5fb341d2 >>>> change-id: 20250428-map-map_stack-to-vm_nohugepage-only-if-thp-is-enabled-ce40a1de095d >>>> >>>> Best regards, >>>> -- >>>> Ignacio Moreno Gonzalez >>>> >>>>