"man 2 migrate_pages" says "On success migrate_pages() returns the number
of pages that could not be moved". Although 5.3 and 5.4 commits fixed
mbind(MPOL_MF_STRICT|MPOL_MF_MOVE*) to fail with EIO when not all pages
could be moved (because some could not be isolated for migration),
migrate_pages(2) was left still reporting only those pages failing at the
migration stage, forgetting those failing at the earlier isolation stage.
Fix that by accumulating a long nr_failed count in struct queue_pages,
returned by queue_pages_range() when it's not returning an error, for
adding on to the nr_failed count from migrate_pages() in mm/migrate.c.
A count of pages? It's more a count of folios, but changing it to pages
would entail more work (also in mm/migrate.c): does not seem justified.
queue_pages_range() itself should only return -EIO in the "strictly
unmovable" case (STRICT without any MOVEs): in that case it's best to
break out as soon as nr_failed gets set; but otherwise it should continue
to isolate pages for MOVing even when nr_failed - as the mbind(2) manpage
promises.
There's a case when nr_failed should be incremented when it was missed:
queue_folios_pte_range() and queue_folios_hugetlb() count the transient
migration entries, like queue_folios_pmd() already did. And there's a
case when nr_failed should not be incremented when it would have been:
in meeting later PTEs of the same large folio, which can only be isolated
once: fixed by recording the current large folio in struct queue_pages.
Clean up the affected functions, fixing or updating many comments. Bool
migrate_folio_add(), without -EIO: true if adding, or if skipping shared
(but its arguable folio_estimated_sharers() heuristic left unchanged).
Use MPOL_MF_WRLOCK flag to queue_pages_range(), instead of bool lock_vma.
Use explicit STRICT|MOVE* flags where queue_pages_test_walk() checks for
skipping, instead of hiding them behind MPOL_MF_VALID.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/mempolicy.c | 342 ++++++++++++++++++++++++---------------------------
1 file changed, 161 insertions(+), 181 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 38a47fa33ef4..752d880dcdf8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -111,7 +111,8 @@
/* Internal flags */
#define MPOL_MF_DISCONTIG_OK (MPOL_MF_INTERNAL << 0) /* Skip checks for continuous vmas */
-#define MPOL_MF_INVERT (MPOL_MF_INTERNAL << 1) /* Invert check for nodemask */
+#define MPOL_MF_INVERT (MPOL_MF_INTERNAL << 1) /* Invert check for nodemask */
+#define MPOL_MF_WRLOCK (MPOL_MF_INTERNAL << 2) /* Write-lock walked vmas */
static struct kmem_cache *policy_cache;
static struct kmem_cache *sn_cache;
@@ -416,9 +417,19 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
},
};
-static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
+static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
unsigned long flags);
+static bool strictly_unmovable(unsigned long flags)
+{
+ /*
+ * STRICT without MOVE flags lets do_mbind() fail immediately with -EIO
+ * if any misplaced page is found.
+ */
+ return (flags & (MPOL_MF_STRICT | MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ==
+ MPOL_MF_STRICT;
+}
+
struct queue_pages {
struct list_head *pagelist;
unsigned long flags;
@@ -426,7 +437,8 @@ struct queue_pages {
unsigned long start;
unsigned long end;
struct vm_area_struct *first;
- bool has_unmovable;
+ struct folio *large; /* note last large folio encountered */
+ long nr_failed; /* could not be isolated at this time */
};
/*
@@ -444,61 +456,37 @@ static inline bool queue_folio_required(struct folio *folio,
return node_isset(nid, *qp->nmask) == !(flags & MPOL_MF_INVERT);
}
-/*
- * queue_folios_pmd() has three possible return values:
- * 0 - folios are placed on the right node or queued successfully, or
- * special page is met, i.e. zero page, or unmovable page is found
- * but continue walking (indicated by queue_pages.has_unmovable).
- * -EIO - is migration entry or only MPOL_MF_STRICT was specified and an
- * existing folio was already on a node that does not follow the
- * policy.
- */
-static int queue_folios_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr,
- unsigned long end, struct mm_walk *walk)
- __releases(ptl)
+static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
{
- int ret = 0;
struct folio *folio;
struct queue_pages *qp = walk->private;
- unsigned long flags;
if (unlikely(is_pmd_migration_entry(*pmd))) {
- ret = -EIO;
- goto unlock;
+ qp->nr_failed++;
+ return;
}
folio = pfn_folio(pmd_pfn(*pmd));
if (is_huge_zero_page(&folio->page)) {
walk->action = ACTION_CONTINUE;
- goto unlock;
+ return;
}
if (!queue_folio_required(folio, qp))
- goto unlock;
-
- flags = qp->flags;
- /* go to folio migration */
- if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
- if (!vma_migratable(walk->vma) ||
- migrate_folio_add(folio, qp->pagelist, flags)) {
- qp->has_unmovable = true;
- goto unlock;
- }
- } else
- ret = -EIO;
-unlock:
- spin_unlock(ptl);
- return ret;
+ return;
+ if (!(qp->flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ||
+ !vma_migratable(walk->vma) ||
+ !migrate_folio_add(folio, qp->pagelist, qp->flags))
+ qp->nr_failed++;
}
/*
- * Scan through pages checking if pages follow certain conditions,
- * and move them to the pagelist if they do.
+ * Scan through folios, checking if they satisfy the required conditions,
+ * moving them from LRU to local pagelist for migration if they do (or not).
*
- * queue_folios_pte_range() has three possible return values:
- * 0 - folios are placed on the right node or queued successfully, or
- * special page is met, i.e. zero page, or unmovable page is found
- * but continue walking (indicated by queue_pages.has_unmovable).
- * -EIO - only MPOL_MF_STRICT was specified and an existing folio was already
- * on a node that does not follow the policy.
+ * queue_folios_pte_range() has two possible return values:
+ * 0 - continue walking to scan for more, even if an existing folio on the
+ * wrong node could not be isolated and queued for migration.
+ * -EIO - only MPOL_MF_STRICT was specified, without MPOL_MF_MOVE or ..._ALL,
+ * and an existing folio was on a node that does not follow the policy.
*/
static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end, struct mm_walk *walk)
@@ -512,8 +500,11 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
spinlock_t *ptl;
ptl = pmd_trans_huge_lock(pmd, vma);
- if (ptl)
- return queue_folios_pmd(pmd, ptl, addr, end, walk);
+ if (ptl) {
+ queue_folios_pmd(pmd, walk);
+ spin_unlock(ptl);
+ goto out;
+ }
mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
if (!pte) {
@@ -522,8 +513,13 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
}
for (; addr != end; pte++, addr += PAGE_SIZE) {
ptent = ptep_get(pte);
- if (!pte_present(ptent))
+ if (pte_none(ptent))
continue;
+ if (!pte_present(ptent)) {
+ if (is_migration_entry(pte_to_swp_entry(ptent)))
+ qp->nr_failed++;
+ continue;
+ }
folio = vm_normal_folio(vma, addr, ptent);
if (!folio || folio_is_zone_device(folio))
continue;
@@ -535,95 +531,87 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
continue;
if (!queue_folio_required(folio, qp))
continue;
- if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
+ if (folio_test_large(folio)) {
/*
- * MPOL_MF_STRICT must be specified if we get here.
- * Continue walking vmas due to MPOL_MF_MOVE* flags.
+ * A large folio can only be isolated from LRU once,
+ * but may be mapped by many PTEs (and Copy-On-Write may
+ * intersperse PTEs of other, order 0, folios). This is
+ * a common case, so don't mistake it for failure (but
+ * there can be other cases of multi-mapped pages which
+ * this quick check does not help to filter out - and a
+ * search of the pagelist might grow to be prohibitive).
+ *
+ * migrate_pages(&pagelist) returns nr_failed folios, so
+ * check "large" now so that queue_pages_range() returns
+ * a comparable nr_failed folios. This does imply that
+ * if folio could not be isolated for some racy reason
+ * at its first PTE, later PTEs will not give it another
+ * chance of isolation; but keeps the accounting simple.
*/
- if (!vma_migratable(vma))
- qp->has_unmovable = true;
-
- /*
- * Do not abort immediately since there may be
- * temporary off LRU pages in the range. Still
- * need migrate other LRU pages.
- */
- if (migrate_folio_add(folio, qp->pagelist, flags))
- qp->has_unmovable = true;
- } else
- break;
+ if (folio == qp->large)
+ continue;
+ qp->large = folio;
+ }
+ if (!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ||
+ !vma_migratable(vma) ||
+ !migrate_folio_add(folio, qp->pagelist, flags)) {
+ qp->nr_failed++;
+ if (strictly_unmovable(flags))
+ break;
+ }
}
pte_unmap_unlock(mapped_pte, ptl);
cond_resched();
-
- return addr != end ? -EIO : 0;
+out:
+ if (qp->nr_failed && strictly_unmovable(flags))
+ return -EIO;
+ return 0;
}
static int queue_folios_hugetlb(pte_t *pte, unsigned long hmask,
unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
- int ret = 0;
#ifdef CONFIG_HUGETLB_PAGE
struct queue_pages *qp = walk->private;
- unsigned long flags = (qp->flags & MPOL_MF_VALID);
+ unsigned long flags = qp->flags;
struct folio *folio;
spinlock_t *ptl;
pte_t entry;
ptl = huge_pte_lock(hstate_vma(walk->vma), walk->mm, pte);
entry = huge_ptep_get(pte);
- if (!pte_present(entry))
+ if (!pte_present(entry)) {
+ if (unlikely(is_hugetlb_entry_migration(entry)))
+ qp->nr_failed++;
goto unlock;
+ }
folio = pfn_folio(pte_pfn(entry));
if (!queue_folio_required(folio, qp))
goto unlock;
-
- if (flags == MPOL_MF_STRICT) {
- /*
- * STRICT alone means only detecting misplaced folio and no
- * need to further check other vma.
- */
- ret = -EIO;
+ if (!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ||
+ !vma_migratable(walk->vma)) {
+ qp->nr_failed++;
goto unlock;
}
-
- if (!vma_migratable(walk->vma)) {
- /*
- * Must be STRICT with MOVE*, otherwise .test_walk() have
- * stopped walking current vma.
- * Detecting misplaced folio but allow migrating folios which
- * have been queued.
- */
- qp->has_unmovable = true;
- goto unlock;
- }
-
/*
- * With MPOL_MF_MOVE, we try to migrate only unshared folios. If it
- * is shared it is likely not worth migrating.
+ * Unless MPOL_MF_MOVE_ALL, we try to avoid migrating a shared folio.
+ * Choosing not to migrate a shared folio is not counted as a failure.
*
* To check if the folio is shared, ideally we want to make sure
* every page is mapped to the same process. Doing that is very
- * expensive, so check the estimated mapcount of the folio instead.
+ * expensive, so check the estimated sharers of the folio instead.
*/
- if (flags & (MPOL_MF_MOVE_ALL) ||
- (flags & MPOL_MF_MOVE && folio_estimated_sharers(folio) == 1 &&
- !hugetlb_pmd_shared(pte))) {
- if (!isolate_hugetlb(folio, qp->pagelist) &&
- (flags & MPOL_MF_STRICT))
- /*
- * Failed to isolate folio but allow migrating pages
- * which have been queued.
- */
- qp->has_unmovable = true;
- }
+ if ((flags & MPOL_MF_MOVE_ALL) ||
+ (folio_estimated_sharers(folio) == 1 && !hugetlb_pmd_shared(pte)))
+ if (!isolate_hugetlb(folio, qp->pagelist))
+ qp->nr_failed++;
unlock:
spin_unlock(ptl);
-#else
- BUG();
+ if (qp->nr_failed && strictly_unmovable(flags))
+ return -EIO;
#endif
- return ret;
+ return 0;
}
#ifdef CONFIG_NUMA_BALANCING
@@ -704,8 +692,11 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
return 1;
}
- /* queue pages from current vma */
- if (flags & MPOL_MF_VALID)
+ /*
+ * Check page nodes, and queue pages to move, in the current vma.
+ * But if no moving, and no strict checking, the scan can be skipped.
+ */
+ if (flags & (MPOL_MF_STRICT | MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
return 0;
return 1;
}
@@ -727,22 +718,21 @@ static const struct mm_walk_ops queue_pages_lock_vma_walk_ops = {
/*
* Walk through page tables and collect pages to be migrated.
*
- * If pages found in a given range are on a set of nodes (determined by
- * @nodes and @flags,) it's isolated and queued to the pagelist which is
- * passed via @private.
+ * If pages found in a given range are not on the required set of @nodes,
+ * and migration is allowed, they are isolated and queued to @pagelist.
*
- * queue_pages_range() has three possible return values:
- * 1 - there is unmovable page, but MPOL_MF_MOVE* & MPOL_MF_STRICT were
- * specified.
- * 0 - queue pages successfully or no misplaced page.
- * errno - i.e. misplaced pages with MPOL_MF_STRICT specified (-EIO) or
- * memory range specified by nodemask and maxnode points outside
- * your accessible address space (-EFAULT)
+ * queue_pages_range() may return:
+ * 0 - all pages already on the right node, or successfully queued for moving
+ * (or neither strict checking nor moving requested: only range checking).
+ * >0 - this number of misplaced folios could not be queued for moving
+ * (a hugetlbfs page or a transparent huge page being counted as 1).
+ * -EIO - a misplaced page found, when MPOL_MF_STRICT specified without MOVEs.
+ * -EFAULT - a hole in the memory range, when MPOL_MF_DISCONTIG_OK unspecified.
*/
-static int
+static long
queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
nodemask_t *nodes, unsigned long flags,
- struct list_head *pagelist, bool lock_vma)
+ struct list_head *pagelist)
{
int err;
struct queue_pages qp = {
@@ -752,20 +742,17 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
.start = start,
.end = end,
.first = NULL,
- .has_unmovable = false,
};
- const struct mm_walk_ops *ops = lock_vma ?
+ const struct mm_walk_ops *ops = (flags & MPOL_MF_WRLOCK) ?
&queue_pages_lock_vma_walk_ops : &queue_pages_walk_ops;
err = walk_page_range(mm, start, end, ops, &qp);
- if (qp.has_unmovable)
- err = 1;
if (!qp.first)
/* whole range in hole */
err = -EFAULT;
- return err;
+ return err ? : qp.nr_failed;
}
/*
@@ -1028,16 +1015,16 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
}
#ifdef CONFIG_MIGRATION
-static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
+static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
unsigned long flags)
{
/*
- * We try to migrate only unshared folios. If it is shared it
- * is likely not worth migrating.
+ * Unless MPOL_MF_MOVE_ALL, we try to avoid migrating a shared folio.
+ * Choosing not to migrate a shared folio is not counted as a failure.
*
* To check if the folio is shared, ideally we want to make sure
* every page is mapped to the same process. Doing that is very
- * expensive, so check the estimated mapcount of the folio instead.
+ * expensive, so check the estimated sharers of the folio instead.
*/
if ((flags & MPOL_MF_MOVE_ALL) || folio_estimated_sharers(folio) == 1) {
if (folio_isolate_lru(folio)) {
@@ -1045,32 +1032,31 @@ static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
node_stat_mod_folio(folio,
NR_ISOLATED_ANON + folio_is_file_lru(folio),
folio_nr_pages(folio));
- } else if (flags & MPOL_MF_STRICT) {
+ } else {
/*
* Non-movable folio may reach here. And, there may be
* temporary off LRU folios or non-LRU movable folios.
* Treat them as unmovable folios since they can't be
- * isolated, so they can't be moved at the moment. It
- * should return -EIO for this case too.
+ * isolated, so they can't be moved at the moment.
*/
- return -EIO;
+ return false;
}
}
-
- return 0;
+ return true;
}
/*
* Migrate pages from one node to a target node.
* Returns error or the number of pages not migrated.
*/
-static int migrate_to_node(struct mm_struct *mm, int source, int dest,
- int flags)
+static long migrate_to_node(struct mm_struct *mm, int source, int dest,
+ int flags)
{
nodemask_t nmask;
struct vm_area_struct *vma;
LIST_HEAD(pagelist);
- int err = 0;
+ long nr_failed;
+ long err = 0;
struct migration_target_control mtc = {
.nid = dest,
.gfp_mask = GFP_HIGHUSER_MOVABLE | __GFP_THISNODE,
@@ -1079,23 +1065,27 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
nodes_clear(nmask);
node_set(source, nmask);
- /*
- * This does not "check" the range but isolates all pages that
- * need migration. Between passing in the full user address
- * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
- */
- vma = find_vma(mm, 0);
VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
- queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
- flags | MPOL_MF_DISCONTIG_OK, &pagelist, false);
+ vma = find_vma(mm, 0);
+
+ /*
+ * This does not migrate the range, but isolates all pages that
+ * need migration. Between passing in the full user address
+ * space range and MPOL_MF_DISCONTIG_OK, this call cannot fail,
+ * but passes back the count of pages which could not be isolated.
+ */
+ nr_failed = queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
+ flags | MPOL_MF_DISCONTIG_OK, &pagelist);
if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, alloc_migration_target, NULL,
- (unsigned long)&mtc, MIGRATE_SYNC, MR_SYSCALL, NULL);
+ (unsigned long)&mtc, MIGRATE_SYNC, MR_SYSCALL, NULL);
if (err)
putback_movable_pages(&pagelist);
}
+ if (err >= 0)
+ err += nr_failed;
return err;
}
@@ -1108,8 +1098,8 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
const nodemask_t *to, int flags)
{
- int busy = 0;
- int err = 0;
+ long nr_failed = 0;
+ long err = 0;
nodemask_t tmp;
lru_cache_disable();
@@ -1191,7 +1181,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
node_clear(source, tmp);
err = migrate_to_node(mm, source, dest, flags);
if (err > 0)
- busy += err;
+ nr_failed += err;
if (err < 0)
break;
}
@@ -1200,8 +1190,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
lru_cache_enable();
if (err < 0)
return err;
- return busy;
-
+ return (nr_failed < INT_MAX) ? nr_failed : INT_MAX;
}
/*
@@ -1240,10 +1229,10 @@ static struct folio *new_folio(struct folio *src, unsigned long start)
}
#else
-static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
+static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
unsigned long flags)
{
- return -EIO;
+ return false;
}
int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
@@ -1267,8 +1256,8 @@ static long do_mbind(unsigned long start, unsigned long len,
struct vma_iterator vmi;
struct mempolicy *new;
unsigned long end;
- int err;
- int ret;
+ long err;
+ long nr_failed;
LIST_HEAD(pagelist);
if (flags & ~(unsigned long)MPOL_MF_VALID)
@@ -1308,10 +1297,8 @@ static long do_mbind(unsigned long start, unsigned long len,
start, start + len, mode, mode_flags,
nmask ? nodes_addr(*nmask)[0] : NUMA_NO_NODE);
- if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
-
+ if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
lru_cache_disable();
- }
{
NODEMASK_SCRATCH(scratch);
if (scratch) {
@@ -1327,44 +1314,37 @@ static long do_mbind(unsigned long start, unsigned long len,
goto mpol_out;
/*
- * Lock the VMAs before scanning for pages to migrate, to ensure we don't
- * miss a concurrently inserted page.
+ * Lock the VMAs before scanning for pages to migrate,
+ * to ensure we don't miss a concurrently inserted page.
*/
- ret = queue_pages_range(mm, start, end, nmask,
- flags | MPOL_MF_INVERT, &pagelist, true);
+ nr_failed = queue_pages_range(mm, start, end, nmask,
+ flags | MPOL_MF_INVERT | MPOL_MF_WRLOCK, &pagelist);
- if (ret < 0) {
- err = ret;
- goto up_out;
- }
-
- vma_iter_init(&vmi, mm, start);
- prev = vma_prev(&vmi);
- for_each_vma_range(vmi, vma, end) {
- err = mbind_range(&vmi, vma, &prev, start, end, new);
- if (err)
- break;
+ if (nr_failed < 0) {
+ err = nr_failed;
+ } else {
+ vma_iter_init(&vmi, mm, start);
+ prev = vma_prev(&vmi);
+ for_each_vma_range(vmi, vma, end) {
+ err = mbind_range(&vmi, vma, &prev, start, end, new);
+ if (err)
+ break;
+ }
}
if (!err) {
- int nr_failed = 0;
-
if (!list_empty(&pagelist)) {
WARN_ON_ONCE(flags & MPOL_MF_LAZY);
- nr_failed = migrate_pages(&pagelist, new_folio, NULL,
+ nr_failed |= migrate_pages(&pagelist, new_folio, NULL,
start, MIGRATE_SYNC, MR_MEMPOLICY_MBIND, NULL);
- if (nr_failed)
- putback_movable_pages(&pagelist);
}
-
- if (((ret > 0) || nr_failed) && (flags & MPOL_MF_STRICT))
+ if (nr_failed && (flags & MPOL_MF_STRICT))
err = -EIO;
- } else {
-up_out:
- if (!list_empty(&pagelist))
- putback_movable_pages(&pagelist);
}
+ if (!list_empty(&pagelist))
+ putback_movable_pages(&pagelist);
+
mmap_write_unlock(mm);
mpol_out:
mpol_put(new);
--
2.35.3
