Re: [PATCH v11 3/6] mm: make alloc_contig_range work at pageblock granularity

[Zi Yan <ziy@nvidia.com>]

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>
> From fce466e89e50bcb0ebb56d7809db1b8bbea47628 Mon Sep 17 00:00:00 2001
> From: Zi Yan <ziy@nvidia.com>
> Date: Tue, 26 Apr 2022 23:00:33 -0400
> Subject: [PATCH] mm: make alloc_contig_range work at pageblock granularity
>
> alloc_contig_range() worked at MAX_ORDER_NR_PAGES 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 by 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 in the
> aforementioned way.
>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>  include/linux/page-isolation.h |   4 +-
>  mm/internal.h                  |   6 +
>  mm/memory_hotplug.c            |   3 +-
>  mm/page_alloc.c                |  54 +++++++--
>  mm/page_isolation.c            | 193 ++++++++++++++++++++++++++++++++-
>  5 files changed, 242 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index e14eddf6741a..5456b7be38ae 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -42,7 +42,7 @@ 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);
> +			 int migratetype, int flags, gfp_t gfp_flags);
>
>  /*
>   * Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.
> @@ -50,7 +50,7 @@ start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
>   */
>  void
>  undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> -			unsigned migratetype);
> +			int migratetype);
>
>  /*
>   * Test all pages in [start_pfn, end_pfn) are isolated or not.
> diff --git a/mm/internal.h b/mm/internal.h
> index 919fa07e1031..0667abd57634 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -359,6 +359,9 @@ extern void *memmap_alloc(phys_addr_t size, phys_addr_t align,
>  			  phys_addr_t min_addr,
>  			  int nid, bool exact_nid);
>
> +void split_free_page(struct page *free_page,
> +				int order, unsigned long split_pfn_offset);
> +
>  #if defined CONFIG_COMPACTION || defined CONFIG_CMA
>
>  /*
> @@ -422,6 +425,9 @@ isolate_freepages_range(struct compact_control *cc,
>  int
>  isolate_migratepages_range(struct compact_control *cc,
>  			   unsigned long low_pfn, unsigned long end_pfn);
> +
> +int __alloc_contig_migrate_range(struct compact_control *cc,
> +					unsigned long start, unsigned long end);
>  #endif
>  int find_suitable_fallback(struct free_area *area, unsigned int order,
>  			int migratetype, bool only_stealable, bool *can_steal);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 4c6065e5d274..9f8ae4cb77ee 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1845,7 +1845,8 @@ 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;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 93dbe05a6029..6a0d1746c095 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1094,6 +1094,43 @@ static inline void __free_one_page(struct page *page,
>  		page_reporting_notify_free(order);
>  }
>
> +/**
> + * 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.
> + */
> +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 = ffs(split_pfn_offset) - 1;
> +		__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);
> +}
>  /*
>   * A bad page could be due to a number of fields. Instead of multiple branches,
>   * try and check multiple fields with one check. The caller must do a detailed
> @@ -8919,7 +8956,7 @@ 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. */
> @@ -9002,7 +9039,7 @@ 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;
> +	int order;
>  	int ret = 0;
>
>  	struct compact_control cc = {
> @@ -9021,14 +9058,11 @@ 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
> @@ -9042,9 +9076,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  	 */
>
>  	ret = start_isolate_page_range(pfn_max_align_down(start),
> -				       pfn_max_align_up(end), migratetype, 0);
> +				pfn_max_align_up(end), migratetype, 0, gfp_mask);
>  	if (ret)
> -		return ret;
> +		goto done;
>
>  	drain_all_pages(cc.zone);
>
> @@ -9064,7 +9098,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  	ret = 0;
>
>  	/*
> -	 * Pages from [start, end) are within a MAX_ORDER_NR_PAGES
> +	 * Pages from [start, end) are within a pageblock_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
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index c2f7a8bb634d..8a0f16d2e4c3 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -203,7 +203,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>  	return -EBUSY;
>  }
>
> -static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> +static void unset_migratetype_isolate(struct page *page, int migratetype)
>  {
>  	struct zone *zone;
>  	unsigned long flags, nr_pages;
> @@ -279,6 +279,166 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
>  	return NULL;
>  }
>
> +/**
> + * 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:	isolate the pageblock before 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.
> + */
> +static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
> +			bool isolate_before)
> +{
> +	unsigned char saved_mt;
> +	unsigned long start_pfn;
> +	unsigned long isolate_pageblock;
> +	unsigned long pfn;
> +	struct zone *zone;
> +
> +	VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));
> +
> +	if (isolate_before)
> +		isolate_pageblock = boundary_pfn - pageblock_nr_pages;
> +	else
> +		isolate_pageblock = boundary_pfn;
> +
> +	/*
> +	 * scan at the beginning of MAX_ORDER_NR_PAGES aligned range to avoid
> +	 * only isolating a subset of pageblocks from a bigger than pageblock
> +	 * free or in-use page. Also make sure all to-be-isolated pageblocks
> +	 * are within the same zone.
> +	 */
> +	zone  = page_zone(pfn_to_page(isolate_pageblock));
> +	start_pfn  = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES),
> +				      zone->zone_start_pfn);
> +
> +	saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
> +	set_pageblock_migratetype(pfn_to_page(isolate_pageblock), MIGRATE_ISOLATE);
> +
> +	/*
> +	 * Bail out early when the to-be-isolated pageblock does not form
> +	 * a free or in-use page across boundary_pfn:
> +	 *
> +	 * 1. isolate before boundary_pfn: the page after is not online
> +	 * 2. isolate after boundary_pfn: the page before is not online
> +	 *
> +	 * This also ensures correctness. Without it, when isolate after
> +	 * boundary_pfn and [start_pfn, boundary_pfn) are not online,
> +	 * __first_valid_page() will return unexpected NULL in the for loop
> +	 * below.
> +	 */
> +	if (isolate_before) {
> +		if (!pfn_to_online_page(boundary_pfn))
> +			return 0;
> +	} else {
> +		if (!pfn_to_online_page(boundary_pfn - 1))
> +			return 0;
> +	}
> +
> +	for (pfn = start_pfn; pfn < boundary_pfn;) {
> +		struct page *page = __first_valid_page(pfn, boundary_pfn - pfn);
> +
> +		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)
> +				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 migration is not possible, just fail.
> +		 */
> +		if (PageCompound(page)) {
> +			unsigned long nr_pages = compound_nr(page);
> +			struct page *head = compound_head(page);
> +			unsigned long head_pfn = page_to_pfn(head);
> +
> +			if (head_pfn + nr_pages < boundary_pfn) {
> +				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;
> +				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 = gfp_flags,
> +					.alloc_contig = true,
> +				};
> +				INIT_LIST_HEAD(&cc.migratepages);
> +
> +				ret = __alloc_contig_migrate_range(&cc, head_pfn,
> +							head_pfn + nr_pages);
> +
> +				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_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.
> +				 */
> +				order = 0;
> +				outer_pfn = pfn;
> +				while (!PageBuddy(pfn_to_page(outer_pfn))) {
> +					if (++order >= MAX_ORDER) {
> +						outer_pfn = pfn;
> +						break;
> +					}
> +					outer_pfn &= ~0UL << order;
> +				}
> +				pfn = outer_pfn;
> +				continue;
> +			} else
> +#endif
> +				goto failed;
> +		}
> +
> +		pfn++;
> +	}
> +	return 0;
> +failed:
> +	/* restore the original migratetype */
> +	set_pageblock_migratetype(pfn_to_page(isolate_pageblock), saved_mt);
> +	return -EBUSY;
> +}
> +
>  /**
>   * start_isolate_page_range() - make page-allocation-type of range of pages to
>   * be MIGRATE_ISOLATE.
> @@ -293,6 +453,8 @@ __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
> @@ -301,6 +463,10 @@ __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.
> @@ -321,21 +487,38 @@ __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)
> +			     int migratetype, int flags, gfp_t gfp_flags)
>  {
>  	unsigned long pfn;
>  	struct page *page;
> +	int ret;
>
>  	BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
>  	BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));
>
> -	for (pfn = start_pfn;
> -	     pfn < end_pfn;
> +	/* isolate [start_pfn, start_pfn + pageblock_nr_pages) pageblock */
> +	ret = isolate_single_pageblock(start_pfn, gfp_flags, false);
> +	if (ret)
> +		return ret;
> +
> +	/* isolate [end_pfn - pageblock_nr_pages, end_pfn) pageblock */
> +	ret = isolate_single_pageblock(end_pfn, gfp_flags, true);
> +	if (ret) {
> +		unset_migratetype_isolate(pfn_to_page(start_pfn), migratetype);
> +		return ret;
> +	}
> +
> +	/* skip isolated pageblocks at the beginning and end */
> +	for (pfn = start_pfn + pageblock_nr_pages;
> +	     pfn < end_pfn - 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(start_pfn, pfn, migratetype);
> +			unset_migratetype_isolate(
> +				pfn_to_page(end_pfn - pageblock_nr_pages),
> +				migratetype);
>  			return -EBUSY;
>  		}
>  	}
> @@ -346,7 +529,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
>   * Make isolated pages available again.
>   */
>  void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> -			    unsigned migratetype)
> +			    int migratetype)
>  {
>  	unsigned long pfn;
>  	struct page *page;
> -- 
> 2.35.1
>
> --
> Best Regards,
> Yan, Zi

To address the infinite loop issue reported by Qian Cai, the follow fixup should be applied to the commit above, another fixup patch should be applied to Patch 4 in this series (I will reply to Patch 4 email) :


diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0c7252ed14a0..76551933bb1d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1114,13 +1114,16 @@ void split_free_page(struct page *free_page,
 	unsigned long flags;
 	int free_page_order;

+	if (split_pfn_offset == 0)
+		return;
+
 	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 = ffs(split_pfn_offset) - 1;
+		free_page_order = min(pfn ? __ffs(pfn) : order, __fls(split_pfn_offset));
 		__free_one_page(pfn_to_page(pfn), pfn, zone, free_page_order,
 				mt, FPI_NONE);
 		pfn += 1UL << free_page_order;
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 8a0f16d2e4c3..7e45736d6451 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -283,6 +283,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * 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
+ * @flags:			isolation flags
  * @gfp_flags:			GFP flags used for migrating pages
  * @isolate_before:	isolate the pageblock before the boundary_pfn
  *
@@ -298,14 +299,15 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * either. The function handles this by splitting the free page or migrating
  * the in-use page then splitting the free page.
  */
-static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
-			bool isolate_before)
+static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
+			gfp_t gfp_flags, bool isolate_before)
 {
 	unsigned char saved_mt;
 	unsigned long start_pfn;
 	unsigned long isolate_pageblock;
 	unsigned long pfn;
 	struct zone *zone;
+	int ret;

 	VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));

@@ -325,7 +327,11 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
 				      zone->zone_start_pfn);

 	saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
-	set_pageblock_migratetype(pfn_to_page(isolate_pageblock), MIGRATE_ISOLATE);
+	ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
+			isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
+
+	if (ret)
+		return ret;

 	/*
 	 * Bail out early when the to-be-isolated pageblock does not form
@@ -374,7 +380,7 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
 			struct page *head = compound_head(page);
 			unsigned long head_pfn = page_to_pfn(head);

-			if (head_pfn + nr_pages < boundary_pfn) {
+			if (head_pfn + nr_pages <= boundary_pfn) {
 				pfn = head_pfn + nr_pages;
 				continue;
 			}
@@ -386,7 +392,8 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
 			if (PageHuge(page) || PageLRU(page) || __PageMovable(page)) {
 				int order;
 				unsigned long outer_pfn;
-				int ret;
+				int page_mt = get_pageblock_migratetype(page);
+				bool isolate_page = !is_migrate_isolate_page(page);
 				struct compact_control cc = {
 					.nr_migratepages = 0,
 					.order = -1,
@@ -399,9 +406,31 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_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);

+				/*
+				 * 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;
 				/*
@@ -417,10 +446,9 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
 				order = 0;
 				outer_pfn = pfn;
 				while (!PageBuddy(pfn_to_page(outer_pfn))) {
-					if (++order >= MAX_ORDER) {
-						outer_pfn = pfn;
-						break;
-					}
+					/* stop if we cannot find the free page */
+					if (++order >= MAX_ORDER)
+						goto failed;
 					outer_pfn &= ~0UL << order;
 				}
 				pfn = outer_pfn;
@@ -435,7 +463,7 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
 	return 0;
 failed:
 	/* restore the original migratetype */
-	set_pageblock_migratetype(pfn_to_page(isolate_pageblock), saved_mt);
+	unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
 	return -EBUSY;
 }

@@ -497,12 +525,12 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));

 	/* isolate [start_pfn, start_pfn + pageblock_nr_pages) pageblock */
-	ret = isolate_single_pageblock(start_pfn, gfp_flags, false);
+	ret = isolate_single_pageblock(start_pfn, flags, gfp_flags, false);
 	if (ret)
 		return ret;

 	/* isolate [end_pfn - pageblock_nr_pages, end_pfn) pageblock */
-	ret = isolate_single_pageblock(end_pfn, gfp_flags, true);
+	ret = isolate_single_pageblock(end_pfn, flags, gfp_flags, true);
 	if (ret) {
 		unset_migratetype_isolate(pfn_to_page(start_pfn), migratetype);
 		return ret;



The complete commit with the fixup patch applied is:

From 71a4c830ce96d23aacb11ec715cc27d482acdd93 Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@nvidia.com>
Date: Thu, 12 May 2022 20:22:58 -0700
Subject: [PATCH] mm: make alloc_contig_range work at pageblock granularity

alloc_contig_range() worked at MAX_ORDER_NR_PAGES 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 by 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 in the
aforementioned way.

[ziy@nvidia.com: fix deadlock/crash]
  Link: https://lkml.kernel.org/r/23A7297E-6C84-4138-A9FE-3598234004E6@nvidia.com
Link: https://lkml.kernel.org/r/20220425143118.2850746-4-zi.yan@sent.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Eric Ren <renzhengeek@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/page-isolation.h |   4 +-
 mm/internal.h                  |   6 +
 mm/memory_hotplug.c            |   3 +-
 mm/page_alloc.c                |  57 +++++++--
 mm/page_isolation.c            | 221 ++++++++++++++++++++++++++++++++-
 5 files changed, 273 insertions(+), 18 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index e14eddf6741a..5456b7be38ae 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -42,7 +42,7 @@ 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);
+			 int migratetype, int flags, gfp_t gfp_flags);

 /*
  * Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.
@@ -50,7 +50,7 @@ start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
  */
 void
 undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
-			unsigned migratetype);
+			int migratetype);

 /*
  * Test all pages in [start_pfn, end_pfn) are isolated or not.
diff --git a/mm/internal.h b/mm/internal.h
index ddd09245a6db..a770029beb08 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -359,6 +359,9 @@ extern void *memmap_alloc(phys_addr_t size, phys_addr_t align,
 			  phys_addr_t min_addr,
 			  int nid, bool exact_nid);

+void split_free_page(struct page *free_page,
+				int order, unsigned long split_pfn_offset);
+
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA

 /*
@@ -422,6 +425,9 @@ isolate_freepages_range(struct compact_control *cc,
 int
 isolate_migratepages_range(struct compact_control *cc,
 			   unsigned long low_pfn, unsigned long end_pfn);
+
+int __alloc_contig_migrate_range(struct compact_control *cc,
+					unsigned long start, unsigned long end);
 #endif
 int find_suitable_fallback(struct free_area *area, unsigned int order,
 			int migratetype, bool only_stealable, bool *can_steal);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e99fd60548f5..945191708ef6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1837,7 +1837,8 @@ 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;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0756f046b644..76551933bb1d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1094,6 +1094,46 @@ static inline void __free_one_page(struct page *page,
 		page_reporting_notify_free(order);
 }

+/**
+ * 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.
+ */
+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;
+
+	if (split_pfn_offset == 0)
+		return;
+
+	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 = min(pfn ? __ffs(pfn) : order, __fls(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);
+}
 /*
  * A bad page could be due to a number of fields. Instead of multiple branches,
  * try and check multiple fields with one check. The caller must do a detailed
@@ -8951,7 +8991,7 @@ 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. */
@@ -9034,7 +9074,7 @@ 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;
+	int order;
 	int ret = 0;

 	struct compact_control cc = {
@@ -9053,14 +9093,11 @@ 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
@@ -9074,9 +9111,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	 */

 	ret = start_isolate_page_range(pfn_max_align_down(start),
-				       pfn_max_align_up(end), migratetype, 0);
+				pfn_max_align_up(end), migratetype, 0, gfp_mask);
 	if (ret)
-		return ret;
+		goto done;

 	drain_all_pages(cc.zone);

@@ -9096,7 +9133,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	ret = 0;

 	/*
-	 * Pages from [start, end) are within a MAX_ORDER_NR_PAGES
+	 * Pages from [start, end) are within a pageblock_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
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c2f7a8bb634d..6b47acaf51f3 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -203,7 +203,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 	return -EBUSY;
 }

-static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
+static void unset_migratetype_isolate(struct page *page, int migratetype)
 {
 	struct zone *zone;
 	unsigned long flags, nr_pages;
@@ -279,6 +279,194 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
 	return NULL;
 }

+/**
+ * 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
+ * @flags:			isolation flags
+ * @gfp_flags:			GFP flags used for migrating pages
+ * @isolate_before:	isolate the pageblock before 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.
+ */
+static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
+			gfp_t gfp_flags, bool isolate_before)
+{
+	unsigned char saved_mt;
+	unsigned long start_pfn;
+	unsigned long isolate_pageblock;
+	unsigned long pfn;
+	struct zone *zone;
+	int ret;
+
+	VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));
+
+	if (isolate_before)
+		isolate_pageblock = boundary_pfn - pageblock_nr_pages;
+	else
+		isolate_pageblock = boundary_pfn;
+
+	/*
+	 * scan at the beginning of MAX_ORDER_NR_PAGES aligned range to avoid
+	 * only isolating a subset of pageblocks from a bigger than pageblock
+	 * free or in-use page. Also make sure all to-be-isolated pageblocks
+	 * are within the same zone.
+	 */
+	zone  = page_zone(pfn_to_page(isolate_pageblock));
+	start_pfn  = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES),
+				      zone->zone_start_pfn);
+
+	saved_mt = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));
+	ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt, flags,
+			isolate_pageblock, isolate_pageblock + pageblock_nr_pages);
+
+	if (ret)
+		return ret;
+
+	/*
+	 * Bail out early when the to-be-isolated pageblock does not form
+	 * a free or in-use page across boundary_pfn:
+	 *
+	 * 1. isolate before boundary_pfn: the page after is not online
+	 * 2. isolate after boundary_pfn: the page before is not online
+	 *
+	 * This also ensures correctness. Without it, when isolate after
+	 * boundary_pfn and [start_pfn, boundary_pfn) are not online,
+	 * __first_valid_page() will return unexpected NULL in the for loop
+	 * below.
+	 */
+	if (isolate_before) {
+		if (!pfn_to_online_page(boundary_pfn))
+			return 0;
+	} else {
+		if (!pfn_to_online_page(boundary_pfn - 1))
+			return 0;
+	}
+
+	for (pfn = start_pfn; pfn < boundary_pfn;) {
+		struct page *page = __first_valid_page(pfn, boundary_pfn - pfn);
+
+		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)
+				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 migration is not possible, just fail.
+		 */
+		if (PageCompound(page)) {
+			unsigned long nr_pages = compound_nr(page);
+			struct page *head = compound_head(page);
+			unsigned long head_pfn = page_to_pfn(head);
+
+			if (head_pfn + nr_pages <= boundary_pfn) {
+				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;
+				int page_mt = get_pageblock_migratetype(page);
+				bool isolate_page = !is_migrate_isolate_page(page);
+				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 = gfp_flags,
+					.alloc_contig = true,
+				};
+				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, boundary_pfn - 1);
+					if (ret)
+						goto failed;
+				}
+
+				ret = __alloc_contig_migrate_range(&cc, head_pfn,
+							head_pfn + nr_pages);
+
+				/*
+				 * 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_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.
+				 */
+				order = 0;
+				outer_pfn = pfn;
+				while (!PageBuddy(pfn_to_page(outer_pfn))) {
+					/* stop if we cannot find the free page */
+					if (++order >= MAX_ORDER)
+						goto failed;
+					outer_pfn &= ~0UL << order;
+				}
+				pfn = outer_pfn;
+				continue;
+			} else
+#endif
+				goto failed;
+		}
+
+		pfn++;
+	}
+	return 0;
+failed:
+	/* restore the original migratetype */
+	unset_migratetype_isolate(pfn_to_page(isolate_pageblock), saved_mt);
+	return -EBUSY;
+}
+
 /**
  * start_isolate_page_range() - make page-allocation-type of range of pages to
  * be MIGRATE_ISOLATE.
@@ -293,6 +481,8 @@ __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
@@ -301,6 +491,10 @@ __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.
@@ -321,21 +515,38 @@ __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)
+			     int migratetype, int flags, gfp_t gfp_flags)
 {
 	unsigned long pfn;
 	struct page *page;
+	int ret;

 	BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
 	BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));

-	for (pfn = start_pfn;
-	     pfn < end_pfn;
+	/* isolate [start_pfn, start_pfn + pageblock_nr_pages) pageblock */
+	ret = isolate_single_pageblock(start_pfn, flags, gfp_flags, false);
+	if (ret)
+		return ret;
+
+	/* isolate [end_pfn - pageblock_nr_pages, end_pfn) pageblock */
+	ret = isolate_single_pageblock(end_pfn, flags, gfp_flags, true);
+	if (ret) {
+		unset_migratetype_isolate(pfn_to_page(start_pfn), migratetype);
+		return ret;
+	}
+
+	/* skip isolated pageblocks at the beginning and end */
+	for (pfn = start_pfn + pageblock_nr_pages;
+	     pfn < end_pfn - 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(start_pfn, pfn, migratetype);
+			unset_migratetype_isolate(
+				pfn_to_page(end_pfn - pageblock_nr_pages),
+				migratetype);
 			return -EBUSY;
 		}
 	}
@@ -346,7 +557,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
  * Make isolated pages available again.
  */
 void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
-			    unsigned migratetype)
+			    int migratetype)
 {
 	unsigned long pfn;
 	struct page *page;
-- 
2.35.1



--
Best Regards,
Yan, Zi

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