From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Subject: mm: enable thp migration for shmem thp My testing for the latest kernel supporting thp migration showed an infinite loop in offlining the memory block that is filled with shmem thps. We can get out of the loop with a signal, but kernel should return with failure in this case. What happens in the loop is that scan_movable_pages() repeats returning the same pfn without any progress. That's because page migration always fails for shmem thps. In memory offline code, memory blocks containing unmovable pages should be prevented from being offline targets by has_unmovable_pages() inside start_isolate_page_range(). So it's possible to change migratability for non-anonymous thps to avoid the issue, but it introduces more complex and thp-specific handling in migration code, so it might not good. So this patch is suggesting to fix the issue by enabling thp migration for shmem thp. Both of anon/shmem thp are migratable so we don't need precheck about the type of thps. Link: http://lkml.kernel.org/r/20180406030706.GA2434@xxxxxxxxxxxxxxxxxxxxxxxxxxxx Fixes: commit 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too early") Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Zi Yan <zi.yan@xxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 5 ++++- mm/migrate.c | 19 ++++++++++++++++--- mm/rmap.c | 3 --- 3 files changed, 20 insertions(+), 7 deletions(-) diff -puN mm/huge_memory.c~mm-enable-thp-migration-for-shmem-thp mm/huge_memory.c --- a/mm/huge_memory.c~mm-enable-thp-migration-for-shmem-thp +++ a/mm/huge_memory.c @@ -2925,7 +2925,10 @@ void remove_migration_pmd(struct page_vm pmde = maybe_pmd_mkwrite(pmde, vma); flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE); - page_add_anon_rmap(new, vma, mmun_start, true); + if (PageAnon(new)) + page_add_anon_rmap(new, vma, mmun_start, true); + else + page_add_file_rmap(new, true); set_pmd_at(mm, mmun_start, pvmw->pmd, pmde); if (vma->vm_flags & VM_LOCKED) mlock_vma_page(new); diff -puN mm/migrate.c~mm-enable-thp-migration-for-shmem-thp mm/migrate.c --- a/mm/migrate.c~mm-enable-thp-migration-for-shmem-thp +++ a/mm/migrate.c @@ -472,7 +472,7 @@ int migrate_page_move_mapping(struct add pslot = radix_tree_lookup_slot(&mapping->i_pages, page_index(page)); - expected_count += 1 + page_has_private(page); + expected_count += hpage_nr_pages(page) + page_has_private(page); if (page_count(page) != expected_count || radix_tree_deref_slot_protected(pslot, &mapping->i_pages.xa_lock) != page) { @@ -505,7 +505,7 @@ int migrate_page_move_mapping(struct add */ newpage->index = page->index; newpage->mapping = page->mapping; - get_page(newpage); /* add cache reference */ + page_ref_add(newpage, hpage_nr_pages(page)); /* add cache reference */ if (PageSwapBacked(page)) { __SetPageSwapBacked(newpage); if (PageSwapCache(page)) { @@ -524,13 +524,26 @@ int migrate_page_move_mapping(struct add } radix_tree_replace_slot(&mapping->i_pages, pslot, newpage); + if (PageTransHuge(page)) { + int i; + int index = page_index(page); + + for (i = 0; i < HPAGE_PMD_NR; i++) { + pslot = radix_tree_lookup_slot(&mapping->i_pages, + index + i); + radix_tree_replace_slot(&mapping->i_pages, pslot, + newpage + i); + } + } else { + radix_tree_replace_slot(&mapping->i_pages, pslot, newpage); + } /* * Drop cache reference from old page by unfreezing * to one less reference. * We know this isn't the last reference. */ - page_ref_unfreeze(page, expected_count - 1); + page_ref_unfreeze(page, expected_count - hpage_nr_pages(page)); xa_unlock(&mapping->i_pages); /* Leave irq disabled to prevent preemption while updating stats */ diff -puN mm/rmap.c~mm-enable-thp-migration-for-shmem-thp mm/rmap.c --- a/mm/rmap.c~mm-enable-thp-migration-for-shmem-thp +++ a/mm/rmap.c @@ -1374,9 +1374,6 @@ static bool try_to_unmap_one(struct page if (!pvmw.pte && (flags & TTU_MIGRATION)) { VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page); - if (!PageAnon(page)) - continue; - set_pmd_migration_entry(&pvmw, page); continue; } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
