From: Michal Hocko <mhocko@xxxxxxxx> Subject: mm: unclutter THP migration THP migration is hacked into the generic migration with rather surprising semantic. The migration allocation callback is supposed to check whether the THP can be migrated at once and if that is not the case then it allocates a simple page to migrate. unmap_and_move then fixes that up by spliting the THP into small pages while moving the head page to the newly allocated order-0 page. Remaning pages are moved to the LRU list by split_huge_page. The same happens if the THP allocation fails. This is really ugly and error prone [1]. I also believe that split_huge_page to the LRU lists is inherently wrong because all tail pages are not migrated. Some callers will just work around that by retrying (e.g. memory hotplug). There are other pfn walkers which are simply broken though. e.g. madvise_inject_error will migrate head and then advances next pfn by the huge page size. do_move_page_to_node_array, queue_pages_range (migrate_pages, mbind), will simply split the THP before migration if the THP migration is not supported then falls back to single page migration but it doesn't handle tail pages if the THP migration path is not able to allocate a fresh THP so we end up with ENOMEM and fail the whole migration which is a questionable behavior. Page compaction doesn't try to migrate large pages so it should be immune. This patch tries to unclutter the situation by moving the special THP handling up to the migrate_pages layer where it actually belongs. We simply split the THP page into the existing list if unmap_and_move fails with ENOMEM and retry. So we will _always_ migrate all THP subpages and specific migrate_pages users do not have to deal with this case in a special way. [1] http://lkml.kernel.org/r/20171121021855.50525-1-zi.yan@xxxxxxxx Link: http://lkml.kernel.org/r/20180103082555.14592-4-mhocko@xxxxxxxxxx Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx> Cc: Andrea Reale <ar@xxxxxxxxxxxxxxxxxx> Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/migrate.h | 4 ++-- mm/huge_memory.c | 6 ++++++ mm/memory_hotplug.c | 2 +- mm/mempolicy.c | 31 +++---------------------------- mm/migrate.c | 34 ++++++++++++++++++++++++---------- 5 files changed, 36 insertions(+), 41 deletions(-) diff -puN include/linux/migrate.h~mm-unclutter-thp-migration include/linux/migrate.h --- a/include/linux/migrate.h~mm-unclutter-thp-migration +++ a/include/linux/migrate.h @@ -42,9 +42,9 @@ static inline struct page *new_page_node return alloc_huge_page_nodemask(page_hstate(compound_head(page)), preferred_nid, nodemask); - if (thp_migration_supported() && PageTransHuge(page)) { - order = HPAGE_PMD_ORDER; + if (PageTransHuge(page)) { gfp_mask |= GFP_TRANSHUGE; + order = HPAGE_PMD_ORDER; } if (PageHighMem(page) || (zone_idx(page_zone(page)) == ZONE_MOVABLE)) diff -puN mm/huge_memory.c~mm-unclutter-thp-migration mm/huge_memory.c --- a/mm/huge_memory.c~mm-unclutter-thp-migration +++ a/mm/huge_memory.c @@ -2401,6 +2401,12 @@ static void __split_huge_page_tail(struc page_tail->index = head->index + tail; page_cpupid_xchg_last(page_tail, page_cpupid_last(head)); + + /* + * always add to the tail because some iterators expect new + * pages to show after the currently processed elements - e.g. + * migrate_pages + */ lru_add_page_tail(head, page_tail, lruvec, list); } diff -puN mm/memory_hotplug.c~mm-unclutter-thp-migration mm/memory_hotplug.c --- a/mm/memory_hotplug.c~mm-unclutter-thp-migration +++ a/mm/memory_hotplug.c @@ -1372,7 +1372,7 @@ do_migrate_range(unsigned long start_pfn if (isolate_huge_page(page, &source)) move_pages -= 1 << compound_order(head); continue; - } else if (thp_migration_supported() && PageTransHuge(page)) + } else if (PageTransHuge(page)) pfn = page_to_pfn(compound_head(page)) + hpage_nr_pages(page) - 1; diff -puN mm/mempolicy.c~mm-unclutter-thp-migration mm/mempolicy.c --- a/mm/mempolicy.c~mm-unclutter-thp-migration +++ a/mm/mempolicy.c @@ -446,15 +446,6 @@ static int queue_pages_pmd(pmd_t *pmd, s __split_huge_pmd(walk->vma, pmd, addr, false, NULL); goto out; } - if (!thp_migration_supported()) { - get_page(page); - spin_unlock(ptl); - lock_page(page); - ret = split_huge_page(page); - unlock_page(page); - put_page(page); - goto out; - } if (!queue_pages_required(page, qp)) { ret = 1; goto unlock; @@ -495,7 +486,7 @@ static int queue_pages_pte_range(pmd_t * if (pmd_trans_unstable(pmd)) return 0; -retry: + pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); for (; addr != end; pte++, addr += PAGE_SIZE) { if (!pte_present(*pte)) @@ -511,22 +502,6 @@ retry: continue; if (!queue_pages_required(page, qp)) continue; - if (PageTransCompound(page) && !thp_migration_supported()) { - get_page(page); - pte_unmap_unlock(pte, ptl); - lock_page(page); - ret = split_huge_page(page); - unlock_page(page); - put_page(page); - /* Failed to split -- skip. */ - if (ret) { - pte = pte_offset_map_lock(walk->mm, pmd, - addr, &ptl); - continue; - } - goto retry; - } - migrate_page_add(page, qp->pagelist, flags); } pte_unmap_unlock(pte - 1, ptl); @@ -948,7 +923,7 @@ struct page *alloc_new_node_page(struct if (PageHuge(page)) return alloc_huge_page_node(page_hstate(compound_head(page)), node); - else if (thp_migration_supported() && PageTransHuge(page)) { + else if (PageTransHuge(page)) { struct page *thp; thp = alloc_pages_node(node, @@ -1124,7 +1099,7 @@ static struct page *new_page(struct page if (PageHuge(page)) { return alloc_huge_page_vma(page_hstate(compound_head(page)), vma, address); - } else if (thp_migration_supported() && PageTransHuge(page)) { + } else if (PageTransHuge(page)) { struct page *thp; thp = alloc_hugepage_vma(GFP_TRANSHUGE, vma, address, diff -puN mm/migrate.c~mm-unclutter-thp-migration mm/migrate.c --- a/mm/migrate.c~mm-unclutter-thp-migration +++ a/mm/migrate.c @@ -1139,6 +1139,9 @@ static ICE_noinline int unmap_and_move(n int rc = MIGRATEPAGE_SUCCESS; struct page *newpage; + if (!thp_migration_supported() && PageTransHuge(page)) + return -ENOMEM; + newpage = get_new_page(page, private); if (!newpage) return -ENOMEM; @@ -1160,14 +1163,6 @@ static ICE_noinline int unmap_and_move(n goto out; } - if (unlikely(PageTransHuge(page) && !PageTransHuge(newpage))) { - lock_page(page); - rc = split_huge_page(page); - unlock_page(page); - if (rc) - goto out; - } - rc = __unmap_and_move(page, newpage, force, mode); if (rc == MIGRATEPAGE_SUCCESS) set_page_owner_migrate_reason(newpage, reason); @@ -1381,6 +1376,7 @@ int migrate_pages(struct list_head *from retry = 0; list_for_each_entry_safe(page, page2, from, lru) { +retry: cond_resched(); if (PageHuge(page)) @@ -1394,6 +1390,26 @@ int migrate_pages(struct list_head *from switch(rc) { case -ENOMEM: + /* + * THP migration might be unsupported or the + * allocation could've failed so we should + * retry on the same page with the THP split + * to base pages. + * + * Head page is retried immediately and tail + * pages are added to the tail of the list so + * we encounter them after the rest of the list + * is processed. + */ + if (PageTransHuge(page)) { + lock_page(page); + rc = split_huge_page_to_list(page, from); + unlock_page(page); + if (!rc) { + list_safe_reset_next(page, page2, lru); + goto retry; + } + } nr_failed++; goto out; case -EAGAIN: @@ -1480,8 +1496,6 @@ static int add_page_for_migration(struct /* FOLL_DUMP to ignore special (like zero) pages */ follflags = FOLL_GET | FOLL_DUMP; - if (!thp_migration_supported()) - follflags |= FOLL_SPLIT; page = follow_page(vma, addr, follflags); err = PTR_ERR(page); _ -- 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
