mm: make alloc_contig_range work at pageblock granularity

alloc_contig_range() worked at MAX_ORDER-1 granularity to avoid merging
pageblocks with different migratetypes. It might unnecessarily convert
extra pageblocks at the beginning and at the end of the range. Change
alloc_contig_range() to work at pageblock granularity.

Special handling is needed for free pages and in-use pages across the
boundaries of the range specified alloc_contig_range(). Because these
partially isolated pages causes free page accounting issues. The free
pages will be split and freed into separate migratetype lists; the
in-use pages will be migrated then the freed pages will be handled.

Signed-off-by: Zi Yan <ziy@nvidia.com>

include/linux/page-isolation.h

@@ -54,7 +54,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
  */
 int
 start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
-			 unsigned migratetype, int flags);
+			 unsigned migratetype, int flags, gfp_t gfp_flags);
 
 /*
  * Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.

mm/internal.h

@@ -319,6 +319,9 @@ isolate_freepages_range(struct compact_control *cc,
 int
 isolate_migratepages_range(struct compact_control *cc,
 			   unsigned long low_pfn, unsigned long end_pfn);
+
+int
+isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags, int isolate_before_boundary);
 #endif
 int find_suitable_fallback(struct free_area *area, unsigned int order,
 			int migratetype, bool only_stealable, bool *can_steal);

mm/memory_hotplug.c

@@ -1863,7 +1863,8 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 	/* set above range as isolated */
 	ret = start_isolate_page_range(start_pfn, end_pfn,
 				       MIGRATE_MOVABLE,
-				       MEMORY_OFFLINE | REPORT_FAILURE);
+				       MEMORY_OFFLINE | REPORT_FAILURE,
+				       GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL);
 	if (ret) {
 		reason = "failure to isolate range";
 		goto failed_removal_pcplists_disabled;

mm/page_alloc.c

@@ -8985,7 +8985,7 @@ static inline void alloc_contig_dump_pages(struct list_head *page_list)
 #endif
 
 /* [start, end) must belong to a single zone. */
-static int __alloc_contig_migrate_range(struct compact_control *cc,
+int __alloc_contig_migrate_range(struct compact_control *cc,
 					unsigned long start, unsigned long end)
 {
 	/* This function is based on compact_zone() from compaction.c. */
@@ -9043,6 +9043,167 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 	return 0;
 }
 
+/**
+ * split_free_page() -- split a free page at split_pfn_offset
+ * @free_page:		the original free page
+ * @order:		the order of the page
+ * @split_pfn_offset:	split offset within the page
+ *
+ * It is used when the free page crosses two pageblocks with different migratetypes
+ * at split_pfn_offset within the page. The split free page will be put into
+ * separate migratetype lists afterwards. Otherwise, the function achieves
+ * nothing.
+ */
+static inline void split_free_page(struct page *free_page,
+				int order, unsigned long split_pfn_offset)
+{
+	struct zone *zone = page_zone(free_page);
+	unsigned long free_page_pfn = page_to_pfn(free_page);
+	unsigned long pfn;
+	unsigned long flags;
+	int free_page_order;
+
+	spin_lock_irqsave(&zone->lock, flags);
+	del_page_from_free_list(free_page, zone, order);
+	for (pfn = free_page_pfn;
+	     pfn < free_page_pfn + (1UL << order);) {
+		int mt = get_pfnblock_migratetype(pfn_to_page(pfn), pfn);
+
+		free_page_order = order_base_2(split_pfn_offset);
+		__free_one_page(pfn_to_page(pfn), pfn, zone, free_page_order,
+				mt, FPI_NONE);
+		pfn += 1UL << free_page_order;
+		split_pfn_offset -= (1UL << free_page_order);
+		/* we have done the first part, now switch to second part */
+		if (split_pfn_offset == 0)
+			split_pfn_offset = (1UL << order) - (pfn - free_page_pfn);
+	}
+	spin_unlock_irqrestore(&zone->lock, flags);
+}
+
+/**
+ * isolate_single_pageblock() -- tries to isolate a pageblock that might be
+ * within a free or in-use page.
+ * @boundary_pfn:		pageblock-aligned pfn that a page might cross
+ * @gfp_flags:			GFP flags used for migrating pages
+ * @isolate_before_boundary:	isolate the pageblock before (1) or after (0)
+ *				the boundary_pfn
+ *
+ * Free and in-use pages can be as big as MAX_ORDER-1 and contain more than one
+ * pageblock. When not all pageblocks within a page are isolated at the same
+ * time, free page accounting can go wrong. For example, in the case of
+ * MAX_ORDER-1 = pageblock_order + 1, a MAX_ORDER-1 page has two pagelbocks.
+ * [        MAX_ORDER-1          ]
+ * [  pageblock0  |  pageblock1  ]
+ * When either pageblock is isolated, if it is a free page, the page is not
+ * split into separate migratetype lists, which is supposed to; if it is an
+ * in-use page and freed later, __free_one_page() does not split the free page
+ * either. The function handles this by splitting the free page or migrating
+ * the in-use page then splitting the free page.
+ */
+int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
+			int isolate_before_boundary)
+{
+	unsigned char saved_mt;
+	/*
+	 * scan at max(MAX_ORDER_NR_PAGES, pageblock_nr_pages) aligned range to
+	 * avoid isolate pageblocks belonging to a bigger free or in-use page
+	 */
+	unsigned long start_pfn = pfn_max_align_down(boundary_pfn);
+	unsigned long isolated_pageblock_pfn;
+	unsigned long pfn;
+
+	VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));
+
+	if (isolate_before_boundary)
+		isolated_pageblock_pfn = boundary_pfn - pageblock_nr_pages;
+	else
+		isolated_pageblock_pfn = boundary_pfn;
+
+	saved_mt = get_pageblock_migratetype(pfn_to_page(isolated_pageblock_pfn));
+	set_pageblock_migratetype(pfn_to_page(isolated_pageblock_pfn), MIGRATE_ISOLATE);
+
+	for (pfn = start_pfn; pfn < boundary_pfn;) {
+		struct page *page = pfn_to_page(pfn);
+
+		/*
+		 * start_pfn is max(MAX_ORDER_NR_PAGES, pageblock_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)
+				split_free_page(page, order, boundary_pfn - pfn);
+			pfn += (1UL << order);
+			continue;
+		}
+		/*
+		 * migrate compound pages then let the free page handling code
+		 * above do the rest
+		 */
+		if (PageHuge(page) || PageTransCompound(page)) {
+			unsigned long nr_pages = compound_nr(page);
+			int order = compound_order(page);
+			struct page *head = compound_head(page);
+			unsigned long head_pfn = page_to_pfn(head);
+
+			if (head_pfn + nr_pages >= boundary_pfn) {
+				int ret;
+				struct compact_control cc = {
+					.nr_migratepages = 0,
+					.order = -1,
+					.zone = page_zone(pfn_to_page(head_pfn)),
+					.mode = MIGRATE_SYNC,
+					.ignore_skip_hint = true,
+					.no_set_skip_hint = true,
+					.gfp_mask = current_gfp_context(gfp_flags),
+					.alloc_contig = true,
+				};
+
+				INIT_LIST_HEAD(&cc.migratepages);
+
+				ret = __alloc_contig_migrate_range(&cc, head_pfn,
+							head_pfn + nr_pages);
+
+				if (ret) {
+					/* restore the original migratetype */
+					set_pageblock_migratetype(
+						pfn_to_page(isolated_pageblock_pfn),
+						saved_mt);
+					return -EBUSY;
+				}
+				/*
+				 * reset pfn, let the free page handling code
+				 * above 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_ORDER-1, but
+				 * after it is freed, the free page order is not.
+				 * Use pfn within the range to find the head of
+				 * the free page and reset order to 0 if a hugetlb
+				 * page with >MAX_ORDER-1 order is encountered.
+				 */
+				if (order > MAX_ORDER-1)
+					order = 0;
+				while (!PageBuddy(pfn_to_page(pfn))) {
+					order++;
+					pfn &= ~0UL << order;
+				}
+				continue;
+			}
+			pfn += nr_pages;
+			continue;
+		}
+
+		pfn++;
+	}
+	return 0;
+}
+
+
 /**
  * alloc_contig_range() -- tries to allocate given range of pages
  * @start:	start PFN to allocate
@@ -9067,8 +9228,9 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 int alloc_contig_range(unsigned long start, unsigned long end,
 		       unsigned migratetype, gfp_t gfp_mask)
 {
-	unsigned long outer_start, outer_end;
-	unsigned int order;
+	unsigned long outer_end;
+	unsigned long alloc_start = ALIGN_DOWN(start, pageblock_nr_pages);
+	unsigned long alloc_end = ALIGN(end, pageblock_nr_pages);
 	int ret = 0;
 
 	struct compact_control cc = {
@@ -9087,14 +9249,11 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	 * What we do here is we mark all pageblocks in range as
 	 * MIGRATE_ISOLATE.  Because pageblock and max order pages may
 	 * have different sizes, and due to the way page allocator
-	 * work, we align the range to biggest of the two pages so
-	 * that page allocator won't try to merge buddies from
-	 * different pageblocks and change MIGRATE_ISOLATE to some
-	 * other migration type.
+	 * work, start_isolate_page_range() has special handlings for this.
 	 *
 	 * Once the pageblocks are marked as MIGRATE_ISOLATE, we
 	 * migrate the pages from an unaligned range (ie. pages that
-	 * we are interested in).  This will put all the pages in
+	 * we are interested in). This will put all the pages in
 	 * range back to page allocator as MIGRATE_ISOLATE.
 	 *
 	 * When this is done, we take the pages in range from page
@@ -9107,9 +9266,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	 * put back to page allocator so that buddy can use them.
 	 */
 
-	ret = start_isolate_page_range(start, end, migratetype, 0);
+	ret = start_isolate_page_range(start, end, migratetype, 0, gfp_mask);
 	if (ret)
-		return ret;
+		goto done;
 
 	drain_all_pages(cc.zone);
 
@@ -9128,68 +9287,28 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 		goto done;
 	ret = 0;
 
-	/*
-	 * Pages from [start, end) are within a MAX_ORDER_NR_PAGES
-	 * aligned blocks that are marked as MIGRATE_ISOLATE.  What's
-	 * more, all pages in [start, end) are free in page allocator.
-	 * What we are going to do is to allocate all pages from
-	 * [start, end) (that is remove them from page allocator).
-	 *
-	 * The only problem is that pages at the beginning and at the
-	 * end of interesting range may be not aligned with pages that
-	 * page allocator holds, ie. they can be part of higher order
-	 * pages.  Because of this, we reserve the bigger range and
-	 * once this is done free the pages we are not interested in.
-	 *
-	 * We don't have to hold zone->lock here because the pages are
-	 * isolated thus they won't get removed from buddy.
-	 */
-
-	order = 0;
-	outer_start = start;
-	while (!PageBuddy(pfn_to_page(outer_start))) {
-		if (++order >= MAX_ORDER) {
-			outer_start = start;
-			break;
-		}
-		outer_start &= ~0UL << order;
-	}
-
-	if (outer_start != start) {
-		order = buddy_order(pfn_to_page(outer_start));
-
-		/*
-		 * outer_start page could be small order buddy page and
-		 * it doesn't include start page. Adjust outer_start
-		 * in this case to report failed page properly
-		 * on tracepoint in test_pages_isolated()
-		 */
-		if (outer_start + (1UL << order) <= start)
-			outer_start = start;
-	}
-
 	/* Make sure the range is really isolated. */
-	if (test_pages_isolated(outer_start, end, 0)) {
+	if (test_pages_isolated(alloc_start, alloc_end, 0)) {
 		ret = -EBUSY;
 		goto done;
 	}
 
 	/* Grab isolated pages from freelists. */
-	outer_end = isolate_freepages_range(&cc, outer_start, end);
+	outer_end = isolate_freepages_range(&cc, alloc_start, alloc_end);
 	if (!outer_end) {
 		ret = -EBUSY;
 		goto done;
 	}
 
 	/* Free head and tail (if any) */
-	if (start != outer_start)
-		free_contig_range(outer_start, start - outer_start);
-	if (end != outer_end)
-		free_contig_range(end, outer_end - end);
+	if (start != alloc_start)
+		free_contig_range(alloc_start, start - alloc_start);
+	if (end != alloc_end)
+		free_contig_range(end, alloc_end - end);
 
 done:
-	undo_isolate_page_range(pfn_max_align_down(start),
-				pfn_max_align_up(end), migratetype);
+	undo_isolate_page_range(alloc_start,
+				alloc_end, migratetype);
 	return ret;
 }
 EXPORT_SYMBOL(alloc_contig_range);

mm/page_isolation.c

@@ -285,6 +285,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  *					 and PageOffline() pages.
  *			REPORT_FAILURE - report details about the failure to
  *			isolate the range
+ * @gfp_flags:		GFP flags used for migrating pages that sit across the
+ *			range boundaries.
  *
  * Making page-allocation-type to be MIGRATE_ISOLATE means free pages in
  * the range will never be allocated. Any free pages and pages freed in the
@@ -293,6 +295,10 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * pages in the range finally, the caller have to free all pages in the range.
  * test_page_isolated() can be used for test it.
  *
+ * The function first tries to isolate the pageblocks at the beginning and end
+ * of the range, since there might be pages across the range boundaries.
+ * Afterwards, it isolates the rest of the range.
+ *
  * There is no high level synchronization mechanism that prevents two threads
  * from trying to isolate overlapping ranges. If this happens, one thread
  * will notice pageblocks in the overlapping range already set to isolate.
@@ -313,21 +319,38 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * Return: 0 on success and -EBUSY if any part of range cannot be isolated.
  */
 int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
-			     unsigned migratetype, int flags)
+			     unsigned migratetype, int flags, gfp_t gfp_flags)
 {
 	unsigned long pfn;
 	struct page *page;
+	/* isolation is done at page block granularity */
+	unsigned long isolate_start = ALIGN_DOWN(start_pfn, pageblock_nr_pages);
+	unsigned long isolate_end = ALIGN(end_pfn, pageblock_nr_pages);
+	int ret;
 
-	unsigned long isolate_start = pfn_max_align_down(start_pfn);
-	unsigned long isolate_end = pfn_max_align_up(end_pfn);
+	/* isolate [isolate_start, isolate_start + pageblock_nr_pages] pageblock */
+	ret = isolate_single_pageblock(isolate_start, gfp_flags, 0);
+	if (ret)
+		return ret;
+
+	/* isolate [isolate_end - pageblock_nr_pages, isolate_end] pageblock */
+	ret = isolate_single_pageblock(isolate_end, gfp_flags, 1);
+	if (ret) {
+		unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
+		return ret;
+	}
 
-	for (pfn = isolate_start;
-	     pfn < isolate_end;
+	/* skip isolated pageblocks at the beginning and end */
+	for (pfn = isolate_start + pageblock_nr_pages;
+	     pfn < isolate_end - pageblock_nr_pages;
 	     pfn += pageblock_nr_pages) {
 		page = __first_valid_page(pfn, pageblock_nr_pages);
 		if (page && set_migratetype_isolate(page, migratetype, flags,
 					start_pfn, end_pfn)) {
 			undo_isolate_page_range(isolate_start, pfn, migratetype);
+			unset_migratetype_isolate(
+				pfn_to_page(isolate_end - pageblock_nr_pages),
+				migratetype);
 			return -EBUSY;
 		}
 	}