mm: page_isolation: prepare for hygienic freelists

Page isolation currently sets MIGRATE_ISOLATE on a block, then drops
zone->lock and scans the block for straddling buddies to split up. 
Because this happens non-atomically wrt the page allocator, it's possible
for allocations to get a buddy whose first block is a regular pcp
migratetype but whose tail is isolated.  This means that in certain cases
memory can still be allocated after isolation.  It will also trigger the
freelist type hygiene warnings in subsequent patches.

start_isolate_page_range()
  isolate_single_pageblock()
    set_migratetype_isolate(tail)
      lock zone->lock
      move_freepages_block(tail) // nop
      set_pageblock_migratetype(tail)
      unlock zone->lock
                                                     __rmqueue_smallest()
                                                       del_page_from_freelist(head)
                                                       expand(head, head_mt)
                                                         WARN(head_mt != tail_mt)
    start_pfn = ALIGN_DOWN(MAX_ORDER_NR_PAGES)
    for (pfn = start_pfn, pfn < end_pfn)
      if (PageBuddy())
        split_free_page(head)

Introduce a variant of move_freepages_block() provided by the allocator
specifically for page isolation; it moves free pages, converts the block,
and handles the splitting of straddling buddies while holding zone->lock.

The allocator knows that pageblocks and buddies are always naturally
aligned, which means that buddies can only straddle blocks if they're
actually >pageblock_order.  This means the search-and-split part can be
simplified compared to what page isolation used to do.

Also tighten up the page isolation code around the expectations of which
pages can be large, and how they are freed.

Based on extensive discussions with and invaluable input from Zi Yan.

[hannes@cmpxchg.org: work around older gcc warning]
  Link: https://lkml.kernel.org/r/20240321142426.GB777580@cmpxchg.org
Link: https://lkml.kernel.org/r/20240320180429.678181-10-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 32 insertions, 74 deletions

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f84f0981b2df..042937d5abe4 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -178,16 +178,10 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 	unmovable = has_unmovable_pages(check_unmovable_start, check_unmovable_end,
 			migratetype, isol_flags);
 	if (!unmovable) {
-		int nr_pages;
-		int mt = get_pageblock_migratetype(page);
-
-		nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE);
-		/* Block spans zone boundaries? */
-		if (nr_pages == -1) {
+		if (!move_freepages_block_isolate(zone, page, MIGRATE_ISOLATE)) {
 			spin_unlock_irqrestore(&zone->lock, flags);
 			return -EBUSY;
 		}
-		__mod_zone_freepage_state(zone, -nr_pages, mt);
 		zone->nr_isolate_pageblock++;
 		spin_unlock_irqrestore(&zone->lock, flags);
 		return 0;
@@ -254,13 +248,11 @@ static void unset_migratetype_isolate(struct page *page, int migratetype)
 	 * allocation.
 	 */
 	if (!isolated_page) {
-		int nr_pages = move_freepages_block(zone, page, migratetype);
 		/*
 		 * Isolating this block already succeeded, so this
 		 * should not fail on zone boundaries.
 		 */
-		WARN_ON_ONCE(nr_pages == -1);
-		__mod_zone_freepage_state(zone, nr_pages, migratetype);
+		WARN_ON_ONCE(!move_freepages_block_isolate(zone, page, migratetype));
 	} else {
 		set_pageblock_migratetype(page, migratetype);
 		__putback_isolated_page(page, order, migratetype);
@@ -374,26 +366,29 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 
 		VM_BUG_ON(!page);
 		pfn = page_to_pfn(page);
-		/*
-		 * start_pfn is MAX_ORDER_NR_PAGES aligned, if there is any
-		 * free pages in [start_pfn, boundary_pfn), its head page will
-		 * always be in the range.
-		 */
+
 		if (PageBuddy(page)) {
 			int order = buddy_order(page);
 
-			if (pfn + (1UL << order) > boundary_pfn) {
-				/* free page changed before split, check it again */
-				if (split_free_page(page, order, boundary_pfn - pfn))
-					continue;
-			}
+			/* move_freepages_block_isolate() handled this */
+			VM_WARN_ON_ONCE(pfn + (1 << order) > boundary_pfn);
 
 			pfn += 1UL << order;
 			continue;
 		}
+
 		/*
-		 * migrate compound pages then let the free page handling code
-		 * above do the rest. If migration is not possible, just fail.
+		 * If a compound page is straddling our block, attempt
+		 * to migrate it out of the way.
+		 *
+		 * We don't have to worry about this creating a large
+		 * free page that straddles into our block: gigantic
+		 * pages are freed as order-0 chunks, and LRU pages
+		 * (currently) do not exceed pageblock_order.
+		 *
+		 * The block of interest has already been marked
+		 * MIGRATE_ISOLATE above, so when migration is done it
+		 * will free its pages onto the correct freelists.
 		 */
 		if (PageCompound(page)) {
 			struct page *head = compound_head(page);
@@ -404,16 +399,10 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 				pfn = head_pfn + nr_pages;
 				continue;
 			}
+
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
-			/*
-			 * hugetlb, lru compound (THP), and movable compound pages
-			 * can be migrated. Otherwise, fail the isolation.
-			 */
-			if (PageHuge(page) || PageLRU(page) || __PageMovable(page)) {
-				int order;
-				unsigned long outer_pfn;
+			if (PageHuge(page)) {
 				int page_mt = get_pageblock_migratetype(page);
-				bool isolate_page = !is_migrate_isolate_page(page);
 				struct compact_control cc = {
 					.nr_migratepages = 0,
 					.order = -1,
@@ -426,56 +415,25 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 				};
 				INIT_LIST_HEAD(&cc.migratepages);
 
-				/*
-				 * XXX: mark the page as MIGRATE_ISOLATE so that
-				 * no one else can grab the freed page after migration.
-				 * Ideally, the page should be freed as two separate
-				 * pages to be added into separate migratetype free
-				 * lists.
-				 */
-				if (isolate_page) {
-					ret = set_migratetype_isolate(page, page_mt,
-						flags, head_pfn, head_pfn + nr_pages);
-					if (ret)
-						goto failed;
-				}
-
 				ret = __alloc_contig_migrate_range(&cc, head_pfn,
 							head_pfn + nr_pages, page_mt);
-
-				/*
-				 * restore the page's migratetype so that it can
-				 * be split into separate migratetype free lists
-				 * later.
-				 */
-				if (isolate_page)
-					unset_migratetype_isolate(page, page_mt);
-
 				if (ret)
 					goto failed;
-				/*
-				 * reset pfn to the head of the free page, so
-				 * that the free page handling code above can split
-				 * the free page to the right migratetype list.
-				 *
-				 * head_pfn is not used here as a hugetlb page order
-				 * can be bigger than MAX_PAGE_ORDER, but after it is
-				 * freed, the free page order is not. Use pfn within
-				 * the range to find the head of the free page.
-				 */
-				order = 0;
-				outer_pfn = pfn;
-				while (!PageBuddy(pfn_to_page(outer_pfn))) {
-					/* stop if we cannot find the free page */
-					if (++order > MAX_PAGE_ORDER)
-						goto failed;
-					outer_pfn &= ~0UL << order;
-				}
-				pfn = outer_pfn;
+				pfn = head_pfn + nr_pages;
 				continue;
-			} else
+			}
+
+			/*
+			 * These pages are movable too, but they're
+			 * not expected to exceed pageblock_order.
+			 *
+			 * Let us know when they do, so we can add
+			 * proper free and split handling for them.
+			 */
+			VM_WARN_ON_ONCE_PAGE(PageLRU(page), page);
+			VM_WARN_ON_ONCE_PAGE(__PageMovable(page), page);
 #endif
-				goto failed;
+			goto failed;
 		}
 
 		pfn++;