On Thu, Aug 01, 2013 at 11:29:39AM +0530, Aneesh Kumar K.V wrote: > Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> writes: > > > On Wed, Jul 31, 2013 at 12:02:30AM +0530, Aneesh Kumar K.V wrote: > >> Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> 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. > > Considering that we have architectures that won't support migrating > explicit hugepages with this patch series, is it ok to use > GFP_HIGHUSER_MOVABLE for hugepage allocation ? Originally this parameter was introduced to make hugepage pool on ZONE_MOVABLE. The benefit is that we can extend the hugepage pool more easily, because external fragmentation less likely happens than other zone type by rearranging fragmented pages with page migration/reclaim. So I think using ZONE_MOVABLE for hugepage allocation by default makes sense even on the architectures which don't support hugepage migration. Thanks, Naoya Horiguchi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>