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WrmuSo491tdOCb0FieecIdWg4U5bHfbfvD5UkK2dispLBn3jA6jGjYXoIcQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. > > 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! > > 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 >> >>