mm/gup: longterm pin migration cleanup

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.

Link: https://lkml.kernel.org/r/20210215161349.246722-13-pasha.tatashin@soleen.com
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index 91629b5b0636707fc2eb07767da768faecdab651..aa09535cf4d47b439f86c947fba63b14dd819425 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1602,27 +1602,28 @@ struct page *get_dump_page(unsigned long addr)
 #endif /* CONFIG_ELF_CORE */
 
 #ifdef CONFIG_MIGRATION
-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)
@@ -1660,47 +1661,27 @@ check_again:
         * 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;
 }
 #else
-static long check_and_migrate_movable_pages(struct mm_struct *mm,
-                                           unsigned long start,
-                                           unsigned long nr_pages,
+static long check_and_migrate_movable_pages(unsigned long nr_pages,
                                            struct page **pages,
-                                           struct vm_area_struct **vmas,
                                            unsigned int gup_flags)
 {
        return nr_pages;
@@ -1718,22 +1699,22 @@ 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;
 }