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SubjectRe: [PATCH v1] mm: consider non-anonymous thp as unmovable page
On Thu, Apr 05, 2018 at 02:48:30PM +0200, Michal Hocko wrote:
> On Thu 05-04-18 15:28:38, Kirill A. Shutemov wrote:
> > On Thu, Apr 05, 2018 at 10:59:27AM +0200, Michal Hocko wrote:
> > > On Tue 03-04-18 13:54:11, Kirill A. Shutemov wrote:
> > > > On Tue, Apr 03, 2018 at 10:34:51AM +0200, Michal Hocko wrote:
> > > > > On Tue 03-04-18 08:24:06, Naoya Horiguchi wrote:
> > > > > > On Tue, Apr 03, 2018 at 09:59:28AM +0200, Michal Hocko wrote:
> > > > > > > On Tue 03-04-18 13:46:28, Naoya Horiguchi wrote:
> > > > > > > > My testing for the latest kernel supporting thp migration found out 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.
> > > > > > >
> > > > > > > Why does it fail? Shmem pages should be movable without any issues.
> > > > > >
> > > > > > .. because try_to_unmap_one() explicitly skips unmapping for migration.
> > > > > >
> > > > > > #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> > > > > > /* PMD-mapped THP migration entry */
> > > > > > 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;
> > > > > > }
> > > > > > #endif
> > > > > >
> > > > > > When I implemented this code, I felt hard to work on both of anon thp
> > > > > > and shmem thp at one time, so I separated the proposal into smaller steps.
> > > > > > Shmem uses pagecache so we need some non-trivial effort (including testing)
> > > > > > to extend thp migration for shmem. But I think it's a reasonable next step.
> > > > >
> > > > > OK, I see. I have forgot about this part. Please be explicit about that
> > > > > in the changelog. Also the proper fix is to not use movable zone for
> > > > > shmem page THP rather than hack around it in the hotplug specific code
> > > > > IMHO.
> > > >
> > > > No. We should just split the page before running
> > > > try_to_unmap(TTU_MIGRATION) on the page.
> > >
> > > Something like this or it is completely broken. I completely forgot the
> > > whole page_vma_mapped_walk business.
> >
> > No, this wouldn't work. We need to split page, not pmd to make migration
> > work.
>
> RIght, I confused the two. What is the proper layer to fix that then?
> rmap_walk_file?

Maybe something like this? Totally untested.

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index a8a126259bc4..9da8fbd1eb6b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -359,4 +359,22 @@ static inline bool thp_migration_supported(void)
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

+static inline bool PageTransHugeMigratable(struct page *page)
+{
+ return thp_migration_supported() &&
+ PageTransHuge(page) && PageAnon(page);
+}
+
+static inline bool PageTransMigratable(struct page *page)
+{
+ return thp_migration_supported() &&
+ PageTransCompound(page) && PageAnon(page);
+}
+
+static inline bool PageTransNonMigratable(struct page *page)
+{
+ return thp_migration_supported() &&
+ PageTransCompound(page) && !PageAnon(page);
+}
+
#endif /* _LINUX_HUGE_MM_H */
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a2246cf670ba..dd66dfe6d198 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -43,7 +43,7 @@ static inline struct page *new_page_nodemask(struct page *page,
return alloc_huge_page_nodemask(page_hstate(compound_head(page)),
preferred_nid, nodemask);

- if (thp_migration_supported() && PageTransHuge(page)) {
+ if (PageTransHugeMigratable(page)) {
order = HPAGE_PMD_ORDER;
gfp_mask |= GFP_TRANSHUGE;
}
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b2bd52ff7605..0672938abf44 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1381,9 +1381,10 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
if (isolate_huge_page(page, &source))
move_pages -= 1 << compound_order(head);
continue;
- } else if (thp_migration_supported() && PageTransHuge(page))
+ } else if (PageTransHugeMigratable(page)) {
pfn = page_to_pfn(compound_head(page))
+ hpage_nr_pages(page) - 1;
+ }

if (!get_page_unless_zero(page))
continue;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 01cbb7078d6c..482e3f482f1b 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -446,7 +446,7 @@ static int queue_pages_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr,
__split_huge_pmd(walk->vma, pmd, addr, false, NULL);
goto out;
}
- if (!thp_migration_supported()) {
+ if (PageTransNonMigratable(page)) {
get_page(page);
spin_unlock(ptl);
lock_page(page);
@@ -511,7 +511,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
continue;
if (!queue_pages_required(page, qp))
continue;
- if (PageTransCompound(page) && !thp_migration_supported()) {
+ if (PageTransNonMigratable(page)) {
get_page(page);
pte_unmap_unlock(pte, ptl);
lock_page(page);
@@ -947,7 +947,7 @@ static struct page *new_node_page(struct page *page, unsigned long node, int **x
if (PageHuge(page))
return alloc_huge_page_node(page_hstate(compound_head(page)),
node);
- else if (thp_migration_supported() && PageTransHuge(page)) {
+ else if (PageTransHugeMigratable(page)) {
struct page *thp;

thp = alloc_pages_node(node,
@@ -1123,7 +1123,7 @@ static struct page *new_page(struct page *page, unsigned long start, int **x)
if (PageHuge(page)) {
return alloc_huge_page_vma(page_hstate(compound_head(page)),
vma, address);
- } else if (thp_migration_supported() && PageTransHuge(page)) {
+ } else if (PageTransHugeMigratable(page)) {
struct page *thp;

thp = alloc_hugepage_vma(GFP_TRANSHUGE, vma, address,
diff --git a/mm/migrate.c b/mm/migrate.c
index 003886606a22..6d654fecddde 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1470,7 +1470,7 @@ static struct page *new_page_node(struct page *p, unsigned long private,
if (PageHuge(p))
return alloc_huge_page_node(page_hstate(compound_head(p)),
pm->node);
- else if (thp_migration_supported() && PageTransHuge(p)) {
+ else if (PageTransHugeMigratable(p)) {
struct page *thp;

thp = alloc_pages_node(pm->node,
@@ -1537,6 +1537,14 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
*/
goto put_and_set;

+ if (PageTransNonMigratable(page)) {
+ lock_page(page);
+ err = split_huge_page(page);
+ unlock_page(page);
+ if (err)
+ goto put_and_set;
+ }
+
err = -EACCES;
if (page_mapcount(page) > 1 &&
!migrate_all)
--
Kirill A. Shutemov
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