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

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Date:   Tue, 19 Jan 2021 20:43:31 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, vbabka@...e.cz,
        mhocko@...e.com, david@...hat.com, osalvador@...e.de,
        dan.j.williams@...el.com, sashal@...nel.org,
        tyhicks@...ux.microsoft.com, iamjoonsoo.kim@....com,
        mike.kravetz@...cle.com, rostedt@...dmis.org, mingo@...hat.com,
        jgg@...pe.ca, peterz@...radead.org, mgorman@...e.de,
        willy@...radead.org, rientjes@...gle.com, jhubbard@...dia.com,
        linux-doc@...r.kernel.org, ira.weiny@...el.com,
        linux-kselftest@...r.kernel.org
Subject: [PATCH v6 12/14] mm/gup: longterm pin migration cleaup

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@...een.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