On Thu, Mar 10, 2022 at 7:56 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 08.03.22 22:34, Zach O'Keefe wrote: > > In madvise collapse context, we optionally want to be able to ignore > > advice from MADV_NOHUGEPAGE-marked regions. > > > > Add a vm_flags_ignore argument to hugepage_vma_revalidate_pmd_count() > > which can be used to ignore vm flags used when considering thp > > eligibility. > > arch/s390/mm/gmap.c:thp_split_mm() sets VM_NOHUGEPAGE to make sure there > are *really* no thp. Being able to bypass that would break KVM horribly. > > Ignoring MADV_NOHUGEPAGE/VM_NOHUGEPAGE feels like the wrong way to go. > > > What about a prctl instead, to disable any khugepagd activity and just > let that process control it manually? > > -- > Thanks, > > David / dhildenb > Hey David - thanks for reviewing and commenting, and certainly thank you for finding this bug. This seems like good motivation for not ignoring VM_NOHUGEPAGE. arch/powerpc also uses this flag for its own purposes (though it's user-directed in that particular case). prctrl(2) sounds very reasonable to me - thanks for the suggestion! Thanks, Zach
