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5F3oMLCxZMRaiDIGYTXARtmPBpTq4k+emUclE1i7e4M8onoZdNTcN2MkJq3VyjEstRgYF9VK2DC VVga/GLR96/q7ZikTeA== On Mon, Mar 02, 2026 at 08:05:37PM +0100, David Hildenbrand (Arm) wrote: > On 3/2/26 18:43, Lorenzo Stoakes wrote: > > On Mon, Mar 02, 2026 at 06:35:46PM +0100, David Hildenbrand (Arm) wrote: > >> > >>> > >>> I prefer my version at [0]. > >>> > >>> Cleaner to actually pull out the zero_folio into a local variable, and also we > >>> should mark it special to be consistent with other codepaths. > >> > >> I argued in v1 that we should handle it similar to an ordinary move > >> during mremap()->move_huge_pmd() and not split it over two patches. > >> > >> It's still split over two patches, which doesn't make sense. > > > > Yes, let's not do that, I made the same comment. > > > >> > >> https://lore.kernel.org/linux-mm/0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org/ > >> > >> I don't think there is no need to get the folio involved at all if we > >> know that we have a well-prepared PMD (zero folio, makred as special). > >> > >> The less code we have that has to deal with setting PMDs special (and > >> possible messing it up), the better. > > > > Yup I agree, I replied accordingly. That's a more elegant thing than duplicating > > huge zero installation code. > > > > I had just assumed that there was _some reason_ why we wouldn't want to do that > > given the original patch from Suren didn't just do that, and for the sakes of a > > backport no need to think too deep on it. > > > > But you're right I don't think there's any reason we need to diverge from what > > mremap() would do. > > > > That does have: > > > > if (vma_has_uffd_without_event_remap(vma)) > > pmd = clear_uffd_wp_pmd(pmd); > > > > Though rather than unconditonally invoking clear_uffd_wp_pmd(). > > > > Is that correct? > > My conclusion was that UFFDIO_MOVE will never move uffd-wp information > (just like we currently don't do for any moved PTEs). > > mremap() might sometimes. But it also effectively moves all (most) uffd > VMA properties, so it has slightly different semantics. Ack thanks! > > -- > Cheers, > > David Cheers, Lorenzo