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

From: Doug Berger
Date: Wed May 25 2022 - 13:41:10 EST

I am seeing some free memory accounting problems with linux-next that I have bisected to this commit (i.e. b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity").

On an arm64 SMP platform with 4GB total memory and the default 16MB default CMA pool, I am seeing the following after boot with a sysrq Show Memory (e.g. 'echo m > /proc/sysrq-trigger'):

[ 16.015906] sysrq: Show Memory
[ 16.019039] Mem-Info:
[ 16.021348] active_anon:14604 inactive_anon:919 isolated_anon:0
[ 16.021348] active_file:0 inactive_file:0 isolated_file:0
[ 16.021348] unevictable:0 dirty:0 writeback:0
[ 16.021348] slab_reclaimable:3662 slab_unreclaimable:3333
[ 16.021348] mapped:928 shmem:15146 pagetables:63 bounce:0
[ 16.021348] kernel_misc_reclaimable:0
[ 16.021348] free:976766 free_pcp:991 free_cma:7017
[ 16.056937] Node 0 active_anon:58416kB inactive_anon:3676kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:3712kB dirty:0kB writeback:0kB shmem:60584kB writeback_tmp:0kB kernel_stack:1200kB pagetables:252kB all_unreclaimable? no
[ 16.081526] DMA free:3041036kB boost:0kB min:6036kB low:9044kB high:12052kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:3145728kB managed:3029992kB mlocked:0kB bounce:0kB free_pcp:636kB local_pcp:0kB free_cma:28068kB
[ 16.108650] lowmem_reserve[]: 0 0 944 944
[ 16.112746] Normal free:866028kB boost:0kB min:1936kB low:2900kB high:3864kB reserved_highatomic:0KB active_anon:58416kB inactive_anon:3676kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:1048576kB managed:967352kB mlocked:0kB bounce:0kB free_pcp:3328kB local_pcp:864kB free_cma:0kB
[ 16.140393] lowmem_reserve[]: 0 0 0 0
[ 16.144133] DMA: 7*4kB (UMC) 4*8kB (M) 3*16kB (M) 3*32kB (MC) 5*64kB (M) 4*128kB (MC) 5*256kB (UMC) 7*512kB (UM) 5*1024kB (UM) 9*2048kB (UMC) 732*4096kB (MC) = 3027724kB
[ 16.159609] Normal: 149*4kB (UM) 95*8kB (UME) 26*16kB (UME) 8*32kB (ME) 2*64kB (UE) 1*128kB (M) 2*256kB (ME) 2*512kB (ME) 2*1024kB (UM) 0*2048kB 210*4096kB (M) = 866028kB
[ 16.175165] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[ 16.183937] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=32768kB
[ 16.192533] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[ 16.201040] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=64kB
[ 16.209374] 15146 total pagecache pages
[ 16.213246] 0 pages in swap cache
[ 16.216595] Swap cache stats: add 0, delete 0, find 0/0
[ 16.221867] Free swap = 0kB
[ 16.224780] Total swap = 0kB
[ 16.227693] 1048576 pages RAM
[ 16.230694] 0 pages HighMem/MovableOnly
[ 16.234564] 49240 pages reserved
[ 16.237825] 4096 pages cma reserved

Some anomolies in the above are:
free_cma:7017 with only 4096 pages cma reserved
DMA free:3041036kB with only managed:3029992kB

I'm not sure what is going on here, but I am suspicious of split_free_page() since del_page_from_free_list doesn't affect migrate_type accounting, but __free_one_page() can.
Also PageBuddy(page) is being checked without zone->lock in isolate_single_pageblock().

Please investigate this as well.

Thanks!
Doug

On 4/29/2022 6:54 AM, Zi Yan wrote:
On 25 Apr 2022, at 10:31, Zi Yan wrote:

From: Zi Yan <ziy@xxxxxxxxxx>

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.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
include/linux/page-isolation.h | 4 +-
mm/internal.h | 6 ++
mm/memory_hotplug.c | 3 +-
mm/page_alloc.c | 54 ++++++++--
mm/page_isolation.c | 184 ++++++++++++++++++++++++++++++++-
5 files changed, 233 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 ce23ac8ad085..70ddd9a0bcf3 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..94b3467e5ba2 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 +279,157 @@ __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 enabled, just fail.
+ */
+ if (PageHuge(page) || PageTransCompound(page)) {
+#if defined CONFIG_COMPACTION || defined CONFIG_CMA
+ 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);
+ 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);
+
+ if (head_pfn + nr_pages < boundary_pfn) {
+ pfn += nr_pages;
+ continue;
+ }
+
+ ret = __alloc_contig_migrate_range(&cc, head_pfn,
+ head_pfn + nr_pages);
+
+ if (ret)
+ goto failed;
+ /*
+ * 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;
+#else
+ goto failed;
+#endif
+ }
+
+ 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 +444,8 @@ __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 +454,10 @@ __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 +478,38 @@ __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 +520,7 @@ 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

Qian hit a bug caused by this series https://lore.kernel.org/linux-mm/20220426201855.GA1014@qian/
and the fix is:

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 75e454f5cf45..b3f074d1682e 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -367,58 +367,67 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
}
/*
* migrate compound pages then let the free page handling code
- * above do the rest. If migration is not enabled, just fail.
+ * above do the rest. If migration is not possible, just fail.
*/
- if (PageHuge(page) || PageTransCompound(page)) {
-#if defined CONFIG_COMPACTION || defined CONFIG_CMA
+ if (PageCompound(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);
- 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);

if (head_pfn + nr_pages < boundary_pfn) {
- pfn += nr_pages;
+ pfn = head_pfn + nr_pages;
continue;
}
-
- ret = __alloc_contig_migrate_range(&cc, head_pfn,
- head_pfn + nr_pages);
-
- if (ret)
- goto failed;
+#if defined CONFIG_COMPACTION || defined CONFIG_CMA
/*
- * 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.
+ * hugetlb, lru compound (THP), and movable compound pages
+ * can be migrated. Otherwise, fail the isolation.
*/
- if (order > MAX_ORDER-1)
+ 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;
- while (!PageBuddy(pfn_to_page(pfn))) {
- order++;
- pfn &= ~0UL << order;
- }
- continue;
-#else
- goto failed;
+ 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++;