From: Zi Yan <z...@nvidia.com>

Pages are grouped in unit of pageblock_order for mobility. cma and
alloc_contig_range() uses pageblock for isolation and migration, so
aligning PFNs to pageblock_order is necessary. But the PFNs used in cma
and alloc_contig_range() were aligned to max(pageblock_order, MAX_ORDER-1).
This makes no difference than aligning only to pageblock_order, since
if pageblock_order > MAX_ORDER, the PFN is pageblock aligned,
otherwise, the PFN is still pageblock aligned. Drop MAX_ORDER alignment
requirement.

When commit 47118af076f6 ("mm: mmzone: MIGRATE_CMA migration type added")
introduced MIGRATE_CMA, __free_one_page() did not prevent merging
freepages on isolate pagelbock and normal pageblock, thus it required
max(pageblock_order, MAX_ORDER-1) alignment. __free_one_page() has
changed and does prevent such merges.

Signed-off-by: Zi Yan <z...@nvidia.com>
---
 include/linux/mmzone.h  |  5 +----
 kernel/dma/contiguous.c |  2 +-
 mm/cma.c                |  6 ++----
 mm/page_alloc.c         | 12 +++++-------
 4 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 58e744b78c2c..6c61aa41a779 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -54,10 +54,7 @@ enum migratetype {
         *
         * The way to use it is to change migratetype of a range of
         * pageblocks to MIGRATE_CMA which can be done by
-        * __free_pageblock_cma() function.  What is important though
-        * is that a range of pageblocks must be aligned to
-        * MAX_ORDER_NR_PAGES should biggest page be bigger than
-        * a single pageblock.
+        * __free_pageblock_cma() function.
         */
        MIGRATE_CMA,
 #endif
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 3d63d91cba5c..ac35b14b0786 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -399,7 +399,7 @@ static const struct reserved_mem_ops rmem_cma_ops = {
 
 static int __init rmem_cma_setup(struct reserved_mem *rmem)
 {
-       phys_addr_t align = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
+       phys_addr_t align = PAGE_SIZE << pageblock_order;
        phys_addr_t mask = align - 1;
        unsigned long node = rmem->fdt_node;
        bool default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
diff --git a/mm/cma.c b/mm/cma.c
index bc9ca8f3c487..d171158bd418 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -180,8 +180,7 @@ int __init cma_init_reserved_mem(phys_addr_t base, 
phys_addr_t size,
                return -EINVAL;
 
        /* ensure minimal alignment required by mm core */
-       alignment = PAGE_SIZE <<
-                       max_t(unsigned long, MAX_ORDER - 1, pageblock_order);
+       alignment = PAGE_SIZE << pageblock_order;
 
        /* alignment should be aligned with order_per_bit */
        if (!IS_ALIGNED(alignment >> PAGE_SHIFT, 1 << order_per_bit))
@@ -268,8 +267,7 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
         * migratetype page by page allocator's buddy algorithm. In the case,
         * you couldn't get a contiguous memory, which is not what we want.
         */
-       alignment = max(alignment,  (phys_addr_t)PAGE_SIZE <<
-                         max_t(unsigned long, MAX_ORDER - 1, pageblock_order));
+       alignment = max(alignment,  (phys_addr_t)PAGE_SIZE << pageblock_order);
        if (fixed && base & (alignment - 1)) {
                ret = -EINVAL;
                pr_err("Region at %pa must be aligned to %pa bytes\n",
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c5952749ad40..5700f5502d59 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8922,14 +8922,12 @@ struct page *has_unmovable_pages(struct zone *zone, 
struct page *page,
 #ifdef CONFIG_CONTIG_ALLOC
 static unsigned long pfn_max_align_down(unsigned long pfn)
 {
-       return pfn & ~(max_t(unsigned long, MAX_ORDER_NR_PAGES,
-                            pageblock_nr_pages) - 1);
+       return pfn & ~(pageblock_nr_pages - 1);
 }
 
 static unsigned long pfn_max_align_up(unsigned long pfn)
 {
-       return ALIGN(pfn, max_t(unsigned long, MAX_ORDER_NR_PAGES,
-                               pageblock_nr_pages));
+       return ALIGN(pfn, pageblock_nr_pages);
 }
 
 #if defined(CONFIG_DYNAMIC_DEBUG) || \
@@ -9022,8 +9020,8 @@ static int __alloc_contig_migrate_range(struct 
compact_control *cc,
  *                     be either of the two.
  * @gfp_mask:  GFP mask to use during compaction
  *
- * The PFN range does not have to be pageblock or MAX_ORDER_NR_PAGES
- * aligned.  The PFN range must belong to a single zone.
+ * The PFN range does not have to be pageblock aligned. The PFN range must
+ * belong to a single zone.
  *
  * The first thing this routine does is attempt to MIGRATE_ISOLATE all
  * pageblocks in the range.  Once isolated, the pageblocks should not
@@ -9099,7 +9097,7 @@ 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
-- 
2.33.0

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