[PATCH v6 12/14] mm/gup: longterm pin migration cleaup

Pavel Tatashin
2021-01-20T01:49:37Z

When pages are longterm pinned, we must migrated them out of movable zone.
The function that migrates them has a hidden loop with goto. The loop is
to retry on isolation failures, and after successful migration.

Make this code better by moving this loop to the caller.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
---
mm/gup.c | 88 +++++++++++++++++++++++---------------------------------
1 file changed, 36 insertions(+), 52 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index c7abd5b37150..9a5d474b39c2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1548,27 +1548,28 @@ struct page *get_dump_page(unsigned long addr)
}
#endif /* CONFIG_ELF_CORE */

-static long check_and_migrate_movable_pages(struct mm_struct *mm,
- unsigned long start,
- unsigned long nr_pages,
+/*
+ * Check whether all pages are pinnable, if so return number of pages. If some
+ * pages are not pinnable, migrate them, and unpin all pages. Return zero if
+ * pages were migrated, or if some pages were not successfully isolated.
+ * Return negative error if migration fails.
+ */
+static long check_and_migrate_movable_pages(unsigned long nr_pages,
struct page **pages,
- struct vm_area_struct **vmas,
unsigned int gup_flags)
{
- unsigned long i, isolation_error_count;
- bool drain_allow;
+ unsigned long i;
+ unsigned long isolation_error_count = 0;
+ bool drain_allow = true;
LIST_HEAD(movable_page_list);
- long ret = nr_pages;
- struct page *prev_head, *head;
+ long ret = 0;
+ struct page *prev_head = NULL;
+ struct page *head;
struct migration_target_control mtc = {
.nid = NUMA_NO_NODE,
.gfp_mask = GFP_USER | __GFP_NOWARN,
};

-check_again:
- prev_head = NULL;
- isolation_error_count = 0;
- drain_allow = true;
for (i = 0; i < nr_pages; i++) {
head = compound_head(pages[i]);
if (head == prev_head)
@@ -1608,40 +1609,23 @@ static long check_and_migrate_movable_pages(struct mm_struct *mm,
* in the correct zone.
*/
if (list_empty(&movable_page_list) && !isolation_error_count)
- return ret;
+ return nr_pages;

+ if (gup_flags & FOLL_PIN) {
+ unpin_user_pages(pages, nr_pages);
+ } else {
+ for (i = 0; i < nr_pages; i++)
+ put_page(pages[i]);
+ }
if (!list_empty(&movable_page_list)) {
- /*
- * drop the above get_user_pages reference.
- */
- if (gup_flags & FOLL_PIN)
- unpin_user_pages(pages, nr_pages);
- else
- for (i = 0; i < nr_pages; i++)
- put_page(pages[i]);
-
ret = migrate_pages(&movable_page_list, alloc_migration_target,
NULL, (unsigned long)&mtc, MIGRATE_SYNC,
MR_LONGTERM_PIN);
- if (ret) {
- if (!list_empty(&movable_page_list))
- putback_movable_pages(&movable_page_list);
- return ret > 0 ? -ENOMEM : ret;
- }
-
- /* We unpinned pages before migration, pin them again */
- ret = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
- NULL, gup_flags);
- if (ret <= 0)
- return ret;
- nr_pages = ret;
+ if (ret && !list_empty(&movable_page_list))
+ putback_movable_pages(&movable_page_list);
}

- /*
- * check again because pages were unpinned, and we also might have
- * had isolation errors and need more pages to migrate.
- */
- goto check_again;
+ return ret > 0 ? -ENOMEM : ret;
}

/*
@@ -1655,22 +1639,22 @@ static long __gup_longterm_locked(struct mm_struct *mm,
struct vm_area_struct **vmas,
unsigned int gup_flags)
{
- unsigned long flags = 0;
+ unsigned int flags;
long rc;

- if (gup_flags & FOLL_LONGTERM)
- flags = memalloc_pin_save();
-
- rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas, NULL,
- gup_flags);
+ if (!(gup_flags & FOLL_LONGTERM))
+ return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
+ NULL, gup_flags);
+ flags = memalloc_pin_save();
+ do {
+ rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
+ NULL, gup_flags);
+ if (rc <= 0)
+ break;
+ rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
+ } while (!rc);
+ memalloc_pin_restore(flags);

- if (gup_flags & FOLL_LONGTERM) {
- if (rc > 0)
- rc = check_and_migrate_movable_pages(mm, start, rc,
- pages, vmas,
- gup_flags);
- memalloc_pin_restore(flags);
- }
return rc;
}

--
2.25.1