Messages in this thread | | | Date | Wed, 31 Jul 2013 16:24:09 -0400 | From | Naoya Horiguchi <> | Subject | Re: [PATCH 8/8] prepare to remove /proc/sys/vm/hugepages_treat_as_movable |
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On Wed, Jul 31, 2013 at 12:02:30AM +0530, Aneesh Kumar K.V wrote: > Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> writes: > > > Now hugepages are definitely movable. So allocating hugepages from > > ZONE_MOVABLE is natural and we have no reason to keep this parameter. > > In order to allow userspace to prepare for the removal, let's leave > > this sysctl handler as noop for a while. > > I guess you still need to handle architectures for which pmd_huge is > > int pmd_huge(pmd_t pmd) > { > return 0; > } > > embedded powerpc is one. They don't store pte information at the PMD > level. Instead pmd contains a pointer to hugepage directory which > contain huge pte.
It seems that this comment is for the whole series, not just for this patch, right?
Some users of hugepage migration (mbind, move_pages, migrate_pages) walk over page tables to collect hugepages to be migrated, where hugepages are just ignored in such architectures due to pmd_huge. So no problem for these users.
But the other users (softoffline, memory hotremove) choose hugepages to be migrated based on pfn, where they don't check pmd_huge. As you wrote, this can be problematic for such architectures. So I think of adding pmd_huge() check somewhere (in unmap_and_move_huge_page for example) to make it fail for such architectures.
Thanks, Naoya Horiguchi
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