mm, memory_hotplug: deobfuscate migration part of offlining

Michal Hocko · torvalds · commit bb8965bd82fd · 2018-12-28T12:11:50.000-08:00
Memory migration might fail during offlining and we keep retrying in that case. This is currently obfuscated by goto retry loop. The code is hard to follow and as a result it is even suboptimal becase each retry round scans the full range from start_pfn even though we have successfully scanned/migrated [start_pfn, pfn] range already. This is all only because check_pages_isolated failure has to rescan the full range again. De-obfuscate the migration retry loop by promoting it to a real for loop. In fact remove the goto altogether by making it a proper double loop (yeah, gotos are nasty in this specific case). In the end we will get a slightly more optimal code which is better readable. [akpm@linux-foundation.org: reflow comments to 80 cols] Link: http://lkml.kernel.org/r/20181211142741.2607-3-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: William Kucharski <william.kucharski@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
@@ -1607,38 +1607,42 @@ static int __ref __offline_pages(unsigned long start_pfn,
 		goto failed_removal_isolated;
 	}
 
-	pfn = start_pfn;
-repeat:
-	/* start memory hot removal */
-	ret = -EINTR;
-	if (signal_pending(current)) {
-		reason = "signal backoff";
-		goto failed_removal_isolated;
-	}
+	do {
+		for (pfn = start_pfn; pfn;) {
+			if (signal_pending(current)) {
+				ret = -EINTR;
+				reason = "signal backoff";
+				goto failed_removal_isolated;
+			}
 
-	cond_resched();
-	lru_add_drain_all();
-	drain_all_pages(zone);
+			cond_resched();
+			lru_add_drain_all();
+			drain_all_pages(zone);
+
+			pfn = scan_movable_pages(pfn, end_pfn);
+			if (pfn) {
+				/*
+				 * TODO: fatal migration failures should bail
+				 * out
+				 */
+				do_migrate_range(pfn, end_pfn);
+			}
+		}
 
-	pfn = scan_movable_pages(start_pfn, end_pfn);
-	if (pfn) { /* We have movable pages */
-		ret = do_migrate_range(pfn, end_pfn);
-		goto repeat;
-	}
+		/*
+		 * Dissolve free hugepages in the memory block before doing
+		 * offlining actually in order to make hugetlbfs's object
+		 * counting consistent.
+		 */
+		ret = dissolve_free_huge_pages(start_pfn, end_pfn);
+		if (ret) {
+			reason = "failure to dissolve huge pages";
+			goto failed_removal_isolated;
+		}
+		/* check again */
+		offlined_pages = check_pages_isolated(start_pfn, end_pfn);
+	} while (offlined_pages < 0);
 
-	/*
-	 * dissolve free hugepages in the memory block before doing offlining
-	 * actually in order to make hugetlbfs's object counting consistent.
-	 */
-	ret = dissolve_free_huge_pages(start_pfn, end_pfn);
-	if (ret) {
-		reason = "failure to dissolve huge pages";
-		goto failed_removal_isolated;
-	}
-	/* check again */
-	offlined_pages = check_pages_isolated(start_pfn, end_pfn);
-	if (offlined_pages < 0)
-		goto repeat;
 	pr_info("Offlined Pages %ld\n", offlined_pages);
 	/* Ok, all of our target is isolated.
 	   We cannot do rollback at this point. */
