[PATCH v5 0/3] mm: Free contiguous order-0 pages efficiently

[PATCH v5 0/3] mm: Free contiguous order-0 pages efficiently

[Muhammad Usama Anjum]

Hi All,

A recent change to vmalloc caused some performance benchmark regressions (see
[1]). I'm attempting to fix that (and at the same time significantly improve
beyond the baseline) by freeing a contiguous set of order-0 pages as a batch.

At the same time I observed that free_contig_range() was essentially doing the
same thing as vfree() so I've fixed it there too. While at it, optimize the
__free_contig_frozen_range() as well.

Check that the contiguous range falls in the same section. If they aren't enabled,
the if conditions get optimized out by the compiler as memdesc_section() returns 0.
See num_pages_contiguous() for more details about it.

[1] https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com

v6.18      - Before the patch causing regression was added
mm-new     - current latest code
this series - v2 series of these patches

(>0 is faster, <0 is slower, (R)/(I) = statistically significant
Regression/Improvement)

v6.18 vs mm-new
+-----------------+----------------------------------------------------------+-------------------+-------------+
| Benchmark       | Result Class                                             |   v6.18    (base) |    mm-new   |
+=================+==========================================================+===================+=============+
| micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |         653643.33 | (R) -50.92% |
|                 | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |         366167.33 | (R) -11.96% |
|                 | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |         489484.00 | (R) -35.21% |
|                 | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |        1011250.33 | (R) -36.45% |
|                 | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |        1086812.33 | (R) -31.83% |
|                 | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |         657940.00 | (R) -38.62% |
|                 | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |         765422.00 | (R) -24.84% |
|                 | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |        2468585.00 | (R) -37.83% |
|                 | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |        2815758.33 | (R) -26.32% |
|                 | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |        4851969.00 | (R) -37.76% |
|                 | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |        4496257.33 | (R) -31.15% |
|                 | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |         570605.00 |      -8.97% |
|                 | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         500866.00 |      -5.88% |
|                 | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         499733.00 |      -6.95% |
|                 | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |        5266237.67 | (R) -40.19% |
|                 | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |         490284.00 |      -2.10% |
|                 | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |         850986.33 | (R) -48.03% |
|                 | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |        2712106.00 | (R) -40.48% |
|                 | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |         111151.33 |       3.52% |
+-----------------+----------------------------------------------------------+-------------------+-------------+

v6.18 vs mm-new with patches
+-----------------+----------------------------------------------------------+-------------------+--------------+
| Benchmark       | Result Class                                             |   v6.18 (base)    |  this series |
+=================+==========================================================+===================+==============+
| micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |         653643.33 |      -14.02% |
|                 | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |         366167.33 |       -7.23% |
|                 | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |         489484.00 |       -1.57% |
|                 | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |        1011250.33 |        1.57% |
|                 | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |        1086812.33 |   (I) 15.75% |
|                 | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |         657940.00 |    (I) 9.05% |
|                 | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |         765422.00 |   (I) 38.45% |
|                 | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |        2468585.00 |   (I) 12.56% |
|                 | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |        2815758.33 |   (I) 38.61% |
|                 | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |        4851969.00 |   (I) 13.43% |
|                 | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |        4496257.33 |   (I) 49.21% |
|                 | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |         570605.00 |       -8.47% |
|                 | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         500866.00 |       -8.17% |
|                 | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         499733.00 |       -5.54% |
|                 | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |        5266237.67 |    (I) 4.63% |
|                 | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |         490284.00 |        1.53% |
|                 | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |         850986.33 |       -0.00% |
|                 | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |        2712106.00 |        1.22% |
|                 | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |         111151.33 |    (I) 4.98% |
+-----------------+----------------------------------------------------------+-------------------+--------------+

mm-new vs vmalloc_2 results are in 2/3 patch.

So this series is mitigating the regression on average as results show -14% to 49% improvement.

Thanks,
Muhammad Usama Anjum

---
Changes since v4: (summary)
- Patch 1: move can_free initialization inside the loop
- Patch 1: Use pfn_to_page() for each pfn instead of page++
- Patch 2: Use num_pages_contiguous() instead of raw loop

Chagnes since v3: (summary)
- Introduce __free_contig_range_common() in first patch  and use it in
  3rd patch as well
- Cosmetic changes related to comments and kerneldoc

Changes since v2: (summary)
- Patch 1 and 3:  Rework the loop to check for memory sections
- Patch 2: Rework by removing the BUG on and add helper free_pages_bulk()

Changes since v1:
- Update description
- Rebase on mm-new and rerun benchmarks/tests
- Patch 1: move FPI_PREPARED check and add todo
- Patch 2: Rework catering newer changes in vfree()
- New Patch 3: optimizes __free_contig_frozen_range()

Muhammad Usama Anjum (1):
  mm/page_alloc: Optimize __free_contig_frozen_range()

Ryan Roberts (2):
  mm/page_alloc: Optimize free_contig_range()
  vmalloc: Optimize vfree

 include/linux/gfp.h |   4 ++
 mm/page_alloc.c     | 141 ++++++++++++++++++++++++++++++++++++++++++--
 mm/vmalloc.c        |  16 ++---
 3 files changed, 144 insertions(+), 17 deletions(-)

-- 
2.47.3

[PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Muhammad Usama Anjum]

From: Ryan Roberts <ryan.roberts@arm.com>

Decompose the range of order-0 pages to be freed into the set of largest
possible power-of-2 size and aligned chunks and free them to the pcp or
buddy. This improves on the previous approach which freed each order-0
page individually in a loop. Testing shows performance to be improved by
more than 10x in some cases.

Since each page is order-0, we must decrement each page's reference
count individually and only consider the page for freeing as part of a
high order chunk if the reference count goes to zero. Additionally
free_pages_prepare() must be called for each individual order-0 page
too, so that the struct page state and global accounting state can be
appropriately managed. But once this is done, the resulting high order
chunks can be freed as a unit to the pcp or buddy.

This significantly speeds up the free operation but also has the side
benefit that high order blocks are added to the pcp instead of each page
ending up on the pcp order-0 list; memory remains more readily available
in high orders.

vmalloc will shortly become a user of this new optimized
free_contig_range() since it aggressively allocates high order
non-compound pages, but then calls split_page() to end up with
contiguous order-0 pages. These can now be freed much more efficiently.

The execution time of the following function was measured in a server
class arm64 machine:

static int page_alloc_high_order_test(void)
{
	unsigned int order = HPAGE_PMD_ORDER;
	struct page *page;
	int i;

	for (i = 0; i < 100000; i++) {
		page = alloc_pages(GFP_KERNEL, order);
		if (!page)
			return -1;
		split_page(page, order);
		free_contig_range(page_to_pfn(page), 1UL << order);
	}

	return 0;
}

Execution time before: 4097358 usec
Execution time after:   729831 usec

Perf trace before:

    99.63%     0.00%  kthreadd         [kernel.kallsyms]      [.] kthread
            |
            ---kthread
               0xffffb33c12a26af8
               |
               |--98.13%--0xffffb33c12a26060
               |          |
               |          |--97.37%--free_contig_range
               |          |          |
               |          |          |--94.93%--___free_pages
               |          |          |          |
               |          |          |          |--55.42%--__free_frozen_pages
               |          |          |          |          |
               |          |          |          |           --43.20%--free_frozen_page_commit
               |          |          |          |                     |
               |          |          |          |                      --35.37%--_raw_spin_unlock_irqrestore
               |          |          |          |
               |          |          |          |--11.53%--_raw_spin_trylock
               |          |          |          |
               |          |          |          |--8.19%--__preempt_count_dec_and_test
               |          |          |          |
               |          |          |          |--5.64%--_raw_spin_unlock
               |          |          |          |
               |          |          |          |--2.37%--__get_pfnblock_flags_mask.isra.0
               |          |          |          |
               |          |          |           --1.07%--free_frozen_page_commit
               |          |          |
               |          |           --1.54%--__free_frozen_pages
               |          |
               |           --0.77%--___free_pages
               |
                --0.98%--0xffffb33c12a26078
                          alloc_pages_noprof

Perf trace after:

     8.42%     2.90%  kthreadd         [kernel.kallsyms]         [k] __free_contig_range
            |
            |--5.52%--__free_contig_range
            |          |
            |          |--5.00%--free_prepared_contig_range
            |          |          |
            |          |          |--1.43%--__free_frozen_pages
            |          |          |          |
            |          |          |           --0.51%--free_frozen_page_commit
            |          |          |
            |          |          |--1.08%--_raw_spin_trylock
            |          |          |
            |          |           --0.89%--_raw_spin_unlock
            |          |
            |           --0.52%--free_pages_prepare
            |
             --2.90%--ret_from_fork
                       kthread
                       0xffffae1c12abeaf8
                       0xffffae1c12abe7a0
                       |
                        --2.69%--vfree
                                  __free_contig_range

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
---
Changes since v4:
- Move can_free initialization inside the loop
- Make __free_pages_prepare() static on reviewer's request
- Remove export of __free_contig_range
- Use pfn_to_page() for each pfn instead of page++

Changes since v3:
- Move __free_contig_range() to more generic __free_contig_range_common()
  which will used to free frozen pages as well
- Simplify the loop in __free_contig_range_common()
- Rewrite the comment

Changes since v2:
- Handle different possible section boundries in __free_contig_range()
- Drop the TODO
- Remove return value from __free_contig_range()
- Remove non-functional change from __free_pages_ok()

Changes since v1:
- Rebase on mm-new
- Move FPI_PREPARED check inside __free_pages_prepare() now that
  fpi_flags are already being passed.
- Add todo (Zi Yan)
- Rerun benchmarks
- Convert VM_BUG_ON_PAGE() to VM_WARN_ON_ONCE()
- Rework order calculation in free_prepared_contig_range() and use
  MAX_PAGE_ORDER as high limit instead of pageblock_order as it must
  be up to internal __free_frozen_pages() how it frees them
---
 include/linux/gfp.h |   2 +
 mm/page_alloc.c     | 110 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 108 insertions(+), 4 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index f82d74a77cad8..7c1f9da7c8e56 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -467,6 +467,8 @@ void free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages);
 void free_contig_range(unsigned long pfn, unsigned long nr_pages);
 #endif
 
+void __free_contig_range(unsigned long pfn, unsigned long nr_pages);
+
 DEFINE_FREE(free_page, void *, free_page((unsigned long)_T))
 
 #endif /* __LINUX_GFP_H */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 75ee81445640b..6e8c79ea62f1c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -91,6 +91,9 @@ typedef int __bitwise fpi_t;
 /* Free the page without taking locks. Rely on trylock only. */
 #define FPI_TRYLOCK		((__force fpi_t)BIT(2))
 
+/* free_pages_prepare() has already been called for page(s) being freed. */
+#define FPI_PREPARED		((__force fpi_t)BIT(3))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
@@ -1301,8 +1304,8 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
-__always_inline bool __free_pages_prepare(struct page *page,
-					  unsigned int order, fpi_t fpi_flags)
+static __always_inline bool __free_pages_prepare(struct page *page,
+		unsigned int order, fpi_t fpi_flags)
 {
 	int bad = 0;
 	bool skip_kasan_poison = should_skip_kasan_poison(page);
@@ -1310,6 +1313,9 @@ __always_inline bool __free_pages_prepare(struct page *page,
 	bool compound = PageCompound(page);
 	struct folio *folio = page_folio(page);
 
+	if (fpi_flags & FPI_PREPARED)
+		return true;
+
 	VM_BUG_ON_PAGE(PageTail(page), page);
 
 	trace_mm_page_free(page, order);
@@ -6784,6 +6790,103 @@ void __init page_alloc_sysctl_init(void)
 	register_sysctl_init("vm", page_alloc_sysctl_table);
 }
 
+static void free_prepared_contig_range(struct page *page,
+		unsigned long nr_pages)
+{
+	while (nr_pages) {
+		unsigned long pfn = page_to_pfn(page);
+		unsigned int order;
+
+		/* We are limited by the largest buddy order. */
+		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
+		/* Don't exceed the number of pages to free. */
+		order = min_t(unsigned int, order, ilog2(nr_pages));
+		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
+
+		/*
+		 * Free the chunk as a single block. Our caller has already
+		 * called free_pages_prepare() for each order-0 page.
+		 */
+		__free_frozen_pages(page, order, FPI_PREPARED);
+
+		page += 1UL << order;
+		nr_pages -= 1UL << order;
+	}
+}
+
+static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
+		bool is_frozen)
+{
+	struct page *page, *start = NULL;
+	unsigned long nr_start = 0;
+	unsigned long start_sec;
+	unsigned long i;
+
+	for (i = 0; i < nr_pages; i++) {
+		bool can_free = true;
+
+		/*
+		 * Contiguous PFNs might not have contiguous "struct pages"
+		 * in some kernel configs: page++ across a section boundary
+		 * is undefined. Use pfn_to_page() for each PFN.
+		 */
+		page = pfn_to_page(pfn + i);
+
+		VM_WARN_ON_ONCE(PageHead(page));
+		VM_WARN_ON_ONCE(PageTail(page));
+
+		if (!is_frozen)
+			can_free = put_page_testzero(page);
+
+		if (can_free)
+			can_free = free_pages_prepare(page, 0);
+
+		if (!can_free) {
+			if (start) {
+				free_prepared_contig_range(start, i - nr_start);
+				start = NULL;
+			}
+			continue;
+		}
+
+		if (start && memdesc_section(page->flags) != start_sec) {
+			free_prepared_contig_range(start, i - nr_start);
+			start = page;
+			nr_start = i;
+			start_sec = memdesc_section(page->flags);
+		} else if (!start) {
+			start = page;
+			nr_start = i;
+			start_sec = memdesc_section(page->flags);
+		}
+	}
+
+	if (start)
+		free_prepared_contig_range(start, nr_pages - nr_start);
+}
+
+/**
+ * __free_contig_range - Free contiguous range of order-0 pages.
+ * @pfn: Page frame number of the first page in the range.
+ * @nr_pages: Number of pages to free.
+ *
+ * For each order-0 struct page in the physically contiguous range, put a
+ * reference. Free any page who's reference count falls to zero. The
+ * implementation is functionally equivalent to, but significantly faster than
+ * calling __free_page() for each struct page in a loop.
+ *
+ * Memory allocated with alloc_pages(order>=1) then subsequently split to
+ * order-0 with split_page() is an example of appropriate contiguous pages that
+ * can be freed with this API.
+ *
+ * Context: May be called in interrupt context or while holding a normal
+ * spinlock, but not in NMI context or while holding a raw spinlock.
+ */
+void __free_contig_range(unsigned long pfn, unsigned long nr_pages)
+{
+	__free_contig_range_common(pfn, nr_pages, /* is_frozen= */ false);
+}
+
 #ifdef CONFIG_CONTIG_ALLOC
 /* Usage: See admin-guide/dynamic-debug-howto.rst */
 static void alloc_contig_dump_pages(struct list_head *page_list)
@@ -7330,8 +7433,7 @@ void free_contig_range(unsigned long pfn, unsigned long nr_pages)
 	if (WARN_ON_ONCE(PageHead(pfn_to_page(pfn))))
 		return;
 
-	for (; nr_pages--; pfn++)
-		__free_page(pfn_to_page(pfn));
+	__free_contig_range(pfn, nr_pages);
 }
 EXPORT_SYMBOL(free_contig_range);
 #endif /* CONFIG_CONTIG_ALLOC */
-- 
2.47.3

[PATCH v5 2/3] vmalloc: Optimize vfree

[Muhammad Usama Anjum]

From: Ryan Roberts <ryan.roberts@arm.com>

Whenever vmalloc allocates high order pages (e.g. for a huge mapping) it
must immediately split_page() to order-0 so that it remains compatible
with users that want to access the underlying struct page.
Commit a06157804399 ("mm/vmalloc: request large order pages from buddy
allocator") recently made it much more likely for vmalloc to allocate
high order pages which are subsequently split to order-0.

Unfortunately this had the side effect of causing performance
regressions for tight vmalloc/vfree loops (e.g. test_vmalloc.ko
benchmarks). See Closes: tag. This happens because the high order pages
must be gotten from the buddy but then because they are split to
order-0, when they are freed they are freed to the order-0 pcp.
Previously allocation was for order-0 pages so they were recycled from
the pcp.

It would be preferable if when vmalloc allocates an (e.g.) order-3 page
that it also frees that order-3 page to the order-3 pcp, then the
regression could be removed.

So let's do exactly that; update stats separately first as coalescing is
hard to do correctly without complexity. Use free_pages_bulk() which uses
the new __free_contig_range() API to batch-free contiguous ranges of pfns.
This not only removes the regression, but significantly improves
performance of vfree beyond the baseline.

A selection of test_vmalloc benchmarks running on arm64 server class
system. mm-new is the baseline. Commit a06157804399 ("mm/vmalloc: request
large order pages from buddy allocator") was added in v6.19-rc1 where we
see regressions. Then with this change performance is much better. (>0
is faster, <0 is slower, (R)/(I) = statistically significant
Regression/Improvement):

+-----------------+----------------------------------------------------------+-------------------+--------------------+
| Benchmark       | Result Class                                             |   mm-new          |  this series       |
+=================+==========================================================+===================+====================+
| micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |        1331843.33 |         (I) 67.17% |
|                 | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |         415907.33 |             -5.14% |
|                 | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |         755448.00 |         (I) 53.55% |
|                 | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |        1591331.33 |         (I) 57.26% |
|                 | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |        1594345.67 |         (I) 68.46% |
|                 | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |        1071826.00 |         (I) 79.27% |
|                 | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |        1018385.00 |         (I) 84.17% |
|                 | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |        3970899.67 |         (I) 77.01% |
|                 | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |        3821788.67 |         (I) 89.44% |
|                 | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |        7795968.00 |         (I) 82.67% |
|                 | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |        6530169.67 |        (I) 118.09% |
|                 | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |         626808.33 |             -0.98% |
|                 | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         532145.67 |             -1.68% |
|                 | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         537032.67 |             -0.96% |
|                 | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |        8805069.00 |         (I) 74.58% |
|                 | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |         500824.67 |              4.35% |
|                 | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |        1637554.67 |         (I) 76.99% |
|                 | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |        4556288.67 |         (I) 72.23% |
|                 | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |         107371.00 |             -0.70% |
+-----------------+----------------------------------------------------------+-------------------+--------------------+

Fixes: a06157804399 ("mm/vmalloc: request large order pages from buddy allocator")
Closes: https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com/
Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
---
Changes since v4:
- Use num_pages_contiguous() instead of raw loop

Changes since v3:
- Add kerneldoc comment and update description
- Add tag

Changes since v2:
- Remove BUG_ON in favour of simple implementation as this has never
  been seen to output any bug in the past as well
- Move the free loop to separate function, free_pages_bulk()
- Update stats, lruvec_stat in separate loop

Changes since v1:
- Rebase on mm-new
- Rerun benchmarks
---
 include/linux/gfp.h |  2 ++
 mm/page_alloc.c     | 28 ++++++++++++++++++++++++++++
 mm/vmalloc.c        | 16 +++++-----------
 3 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 7c1f9da7c8e56..71f9097ab99a0 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -239,6 +239,8 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 				struct page **page_array);
 #define __alloc_pages_bulk(...)			alloc_hooks(alloc_pages_bulk_noprof(__VA_ARGS__))
 
+void free_pages_bulk(struct page **page_array, unsigned long nr_pages);
+
 unsigned long alloc_pages_bulk_mempolicy_noprof(gfp_t gfp,
 				unsigned long nr_pages,
 				struct page **page_array);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e8c79ea62f1c..9218fda8842a6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5175,6 +5175,34 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 }
 EXPORT_SYMBOL_GPL(alloc_pages_bulk_noprof);
 
+/*
+ * free_pages_bulk - Free an array of order-0 pages
+ * @page_array: Array of pages to free
+ * @nr_pages: The number of pages in the array
+ *
+ * Free the order-0 pages. Adjacent entries whose PFNs form a contiguous
+ * run are released with a single __free_contig_range() call.
+ *
+ * This assumes page_array is sorted in ascending PFN order. Without that,
+ * the function still frees all pages, but contiguous runs may not be
+ * detected and the freeing pattern can degrade to freeing one page at a
+ * time.
+ *
+ * Context: Sleepable process context only; calls cond_resched()
+ */
+void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
+{
+	while (nr_pages) {
+		unsigned long nr_contig = num_pages_contiguous(page_array, nr_pages);
+
+		__free_contig_range(page_to_pfn(*page_array), nr_contig);
+
+		nr_pages -= nr_contig;
+		page_array += nr_contig;
+		cond_resched();
+	}
+}
+
 /*
  * This is the 'heart' of the zoned buddy allocator.
  */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c607307c657a6..e9b3d6451e48b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3459,19 +3459,13 @@ void vfree(const void *addr)
 
 	if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
 		vm_reset_perms(vm);
-	for (i = 0; i < vm->nr_pages; i++) {
-		struct page *page = vm->pages[i];
 
-		BUG_ON(!page);
-		/*
-		 * High-order allocs for huge vmallocs are split, so
-		 * can be freed as an array of order-0 allocations
-		 */
-		if (!(vm->flags & VM_MAP_PUT_PAGES))
-			mod_lruvec_page_state(page, NR_VMALLOC, -1);
-		__free_page(page);
-		cond_resched();
+	if (!(vm->flags & VM_MAP_PUT_PAGES)) {
+		for (i = 0; i < vm->nr_pages; i++)
+			mod_lruvec_page_state(vm->pages[i], NR_VMALLOC, -1);
 	}
+	free_pages_bulk(vm->pages, vm->nr_pages);
+
 	kvfree(vm->pages);
 	kfree(vm);
 }
-- 
2.47.3

[PATCH v5 3/3] mm/page_alloc: Optimize __free_contig_frozen_range()

[Muhammad Usama Anjum]

Apply the same batch-freeing optimization from free_contig_range() to the
frozen page path. The previous __free_contig_frozen_range() freed each
order-0 page individually via free_frozen_pages(), which is slow for the
same reason the old free_contig_range() was: each page goes to the
order-0 pcp list rather than being coalesced into higher-order blocks.

Rewrite __free_contig_frozen_range() to call free_pages_prepare() for
each order-0 page, then batch the prepared pages into the largest
possible power-of-2 aligned chunks via free_prepared_contig_range().
If free_pages_prepare() fails (e.g. HWPoison, bad page) the page is
deliberately not freed; it should not be returned to the allocator.

I've tested CMA through debugfs. The test allocates 16384 pages per
allocation for several iterations. There is 3.5x improvement.

Before: 1406 usec per iteration
After:   402 usec per iteration

Before:

    70.89%     0.69%  cma              [kernel.kallsyms]      [.] free_contig_frozen_range
            |
            |--70.20%--free_contig_frozen_range
            |          |
            |          |--46.41%--__free_frozen_pages
            |          |          |
            |          |           --36.18%--free_frozen_page_commit
            |          |                     |
            |          |                      --29.63%--_raw_spin_unlock_irqrestore
            |          |
            |          |--8.76%--_raw_spin_trylock
            |          |
            |          |--7.03%--__preempt_count_dec_and_test
            |          |
            |          |--4.57%--_raw_spin_unlock
            |          |
            |          |--1.96%--__get_pfnblock_flags_mask.isra.0
            |          |
            |           --1.15%--free_frozen_page_commit
            |
             --0.69%--el0t_64_sync

After:

    23.57%     0.00%  cma              [kernel.kallsyms]      [.] free_contig_frozen_range
            |
            ---free_contig_frozen_range
               |
               |--20.45%--__free_contig_frozen_range
               |          |
               |          |--17.77%--free_pages_prepare
               |          |
               |           --0.72%--free_prepared_contig_range
               |                     |
               |                      --0.55%--__free_frozen_pages
               |
                --3.12%--free_pages_prepare

Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
---
Changes since v4:
- Use /* */ style comment with boolean variable

Changes since v3:
- Use newly introduced __free_contig_range_common() as the pattern was
  very similar to __free_contig_range()

Changes since v2:
- Rework the loop to check for memory sections just like __free_contig_range()
- Didn't add reviewed-by tags because of rework
---
 mm/page_alloc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9218fda8842a6..b043b56f65c57 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7052,8 +7052,7 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
 
 static void __free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages)
 {
-	for (; nr_pages--; pfn++)
-		free_frozen_pages(pfn_to_page(pfn), 0);
+	__free_contig_range_common(pfn, nr_pages, /* is_frozen= */ true);
 }
 
 /**
-- 
2.47.3

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Zi Yan]

On 31 Mar 2026, at 11:21, Muhammad Usama Anjum wrote:

> From: Ryan Roberts <ryan.roberts@arm.com>
>
> Decompose the range of order-0 pages to be freed into the set of largest
> possible power-of-2 size and aligned chunks and free them to the pcp or
> buddy. This improves on the previous approach which freed each order-0
> page individually in a loop. Testing shows performance to be improved by
> more than 10x in some cases.
>
> Since each page is order-0, we must decrement each page's reference
> count individually and only consider the page for freeing as part of a
> high order chunk if the reference count goes to zero. Additionally
> free_pages_prepare() must be called for each individual order-0 page
> too, so that the struct page state and global accounting state can be
> appropriately managed. But once this is done, the resulting high order
> chunks can be freed as a unit to the pcp or buddy.
>
> This significantly speeds up the free operation but also has the side
> benefit that high order blocks are added to the pcp instead of each page
> ending up on the pcp order-0 list; memory remains more readily available
> in high orders.
>
> vmalloc will shortly become a user of this new optimized
> free_contig_range() since it aggressively allocates high order
> non-compound pages, but then calls split_page() to end up with
> contiguous order-0 pages. These can now be freed much more efficiently.
>
> The execution time of the following function was measured in a server
> class arm64 machine:
>
> static int page_alloc_high_order_test(void)
> {
> 	unsigned int order = HPAGE_PMD_ORDER;
> 	struct page *page;
> 	int i;
>
> 	for (i = 0; i < 100000; i++) {
> 		page = alloc_pages(GFP_KERNEL, order);
> 		if (!page)
> 			return -1;
> 		split_page(page, order);
> 		free_contig_range(page_to_pfn(page), 1UL << order);
> 	}
>
> 	return 0;
> }
>
> Execution time before: 4097358 usec
> Execution time after:   729831 usec
>
> Perf trace before:
>
>     99.63%     0.00%  kthreadd         [kernel.kallsyms]      [.] kthread
>             |
>             ---kthread
>                0xffffb33c12a26af8
>                |
>                |--98.13%--0xffffb33c12a26060
>                |          |
>                |          |--97.37%--free_contig_range
>                |          |          |
>                |          |          |--94.93%--___free_pages
>                |          |          |          |
>                |          |          |          |--55.42%--__free_frozen_pages
>                |          |          |          |          |
>                |          |          |          |           --43.20%--free_frozen_page_commit
>                |          |          |          |                     |
>                |          |          |          |                      --35.37%--_raw_spin_unlock_irqrestore
>                |          |          |          |
>                |          |          |          |--11.53%--_raw_spin_trylock
>                |          |          |          |
>                |          |          |          |--8.19%--__preempt_count_dec_and_test
>                |          |          |          |
>                |          |          |          |--5.64%--_raw_spin_unlock
>                |          |          |          |
>                |          |          |          |--2.37%--__get_pfnblock_flags_mask.isra.0
>                |          |          |          |
>                |          |          |           --1.07%--free_frozen_page_commit
>                |          |          |
>                |          |           --1.54%--__free_frozen_pages
>                |          |
>                |           --0.77%--___free_pages
>                |
>                 --0.98%--0xffffb33c12a26078
>                           alloc_pages_noprof
>
> Perf trace after:
>
>      8.42%     2.90%  kthreadd         [kernel.kallsyms]         [k] __free_contig_range
>             |
>             |--5.52%--__free_contig_range
>             |          |
>             |          |--5.00%--free_prepared_contig_range
>             |          |          |
>             |          |          |--1.43%--__free_frozen_pages
>             |          |          |          |
>             |          |          |           --0.51%--free_frozen_page_commit
>             |          |          |
>             |          |          |--1.08%--_raw_spin_trylock
>             |          |          |
>             |          |           --0.89%--_raw_spin_unlock
>             |          |
>             |           --0.52%--free_pages_prepare
>             |
>              --2.90%--ret_from_fork
>                        kthread
>                        0xffffae1c12abeaf8
>                        0xffffae1c12abe7a0
>                        |
>                         --2.69%--vfree
>                                   __free_contig_range
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> ---
> Changes since v4:
> - Move can_free initialization inside the loop
> - Make __free_pages_prepare() static on reviewer's request
> - Remove export of __free_contig_range
> - Use pfn_to_page() for each pfn instead of page++
>
> Changes since v3:
> - Move __free_contig_range() to more generic __free_contig_range_common()
>   which will used to free frozen pages as well
> - Simplify the loop in __free_contig_range_common()
> - Rewrite the comment
>
> Changes since v2:
> - Handle different possible section boundries in __free_contig_range()
> - Drop the TODO
> - Remove return value from __free_contig_range()
> - Remove non-functional change from __free_pages_ok()
>
> Changes since v1:
> - Rebase on mm-new
> - Move FPI_PREPARED check inside __free_pages_prepare() now that
>   fpi_flags are already being passed.
> - Add todo (Zi Yan)
> - Rerun benchmarks
> - Convert VM_BUG_ON_PAGE() to VM_WARN_ON_ONCE()
> - Rework order calculation in free_prepared_contig_range() and use
>   MAX_PAGE_ORDER as high limit instead of pageblock_order as it must
>   be up to internal __free_frozen_pages() how it frees them
> ---
>  include/linux/gfp.h |   2 +
>  mm/page_alloc.c     | 110 ++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 108 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index f82d74a77cad8..7c1f9da7c8e56 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -467,6 +467,8 @@ void free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages);
>  void free_contig_range(unsigned long pfn, unsigned long nr_pages);
>  #endif
>
> +void __free_contig_range(unsigned long pfn, unsigned long nr_pages);
> +
>  DEFINE_FREE(free_page, void *, free_page((unsigned long)_T))
>
>  #endif /* __LINUX_GFP_H */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 75ee81445640b..6e8c79ea62f1c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -91,6 +91,9 @@ typedef int __bitwise fpi_t;
>  /* Free the page without taking locks. Rely on trylock only. */
>  #define FPI_TRYLOCK		((__force fpi_t)BIT(2))
>
> +/* free_pages_prepare() has already been called for page(s) being freed. */
> +#define FPI_PREPARED		((__force fpi_t)BIT(3))
> +
>  /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
>  static DEFINE_MUTEX(pcp_batch_high_lock);
>  #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
> @@ -1301,8 +1304,8 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
>
>  #endif /* CONFIG_MEM_ALLOC_PROFILING */
>
> -__always_inline bool __free_pages_prepare(struct page *page,
> -					  unsigned int order, fpi_t fpi_flags)
> +static __always_inline bool __free_pages_prepare(struct page *page,
> +		unsigned int order, fpi_t fpi_flags)
>  {
>  	int bad = 0;
>  	bool skip_kasan_poison = should_skip_kasan_poison(page);
> @@ -1310,6 +1313,9 @@ __always_inline bool __free_pages_prepare(struct page *page,
>  	bool compound = PageCompound(page);
>  	struct folio *folio = page_folio(page);
>
> +	if (fpi_flags & FPI_PREPARED)
> +		return true;
> +
>  	VM_BUG_ON_PAGE(PageTail(page), page);
>
>  	trace_mm_page_free(page, order);
> @@ -6784,6 +6790,103 @@ void __init page_alloc_sysctl_init(void)
>  	register_sysctl_init("vm", page_alloc_sysctl_table);
>  }
>
> +static void free_prepared_contig_range(struct page *page,
> +		unsigned long nr_pages)
> +{
> +	while (nr_pages) {
> +		unsigned long pfn = page_to_pfn(page);

pfn does not change after this assignment. That is why David suggested
prefixing a const. You can send a fixup to this patch to change this
if there is no substantial change needed for this series.

> +		unsigned int order;
> +
> +		/* We are limited by the largest buddy order. */
> +		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
> +		/* Don't exceed the number of pages to free. */
> +		order = min_t(unsigned int, order, ilog2(nr_pages));
> +		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
> +
> +		/*
> +		 * Free the chunk as a single block. Our caller has already
> +		 * called free_pages_prepare() for each order-0 page.
> +		 */
> +		__free_frozen_pages(page, order, FPI_PREPARED);
> +
> +		page += 1UL << order;
> +		nr_pages -= 1UL << order;
> +	}
> +}
> +
> +static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
> +		bool is_frozen)
> +{
> +	struct page *page, *start = NULL;
> +	unsigned long nr_start = 0;
> +	unsigned long start_sec;
> +	unsigned long i;
> +
> +	for (i = 0; i < nr_pages; i++) {
> +		bool can_free = true;
> +
> +		/*
> +		 * Contiguous PFNs might not have contiguous "struct pages"
> +		 * in some kernel configs: page++ across a section boundary
> +		 * is undefined. Use pfn_to_page() for each PFN.
> +		 */
> +		page = pfn_to_page(pfn + i);

page is local to this loop. You probably can move its declaration here.
But feel free to ignore this suggestion.

I was about to suggest make it const, but put_page_test_zero()
and free_pages_prepare() do not accept const struct page yet.

> +
> +		VM_WARN_ON_ONCE(PageHead(page));
> +		VM_WARN_ON_ONCE(PageTail(page));
> +
> +		if (!is_frozen)
> +			can_free = put_page_testzero(page);
> +
> +		if (can_free)
> +			can_free = free_pages_prepare(page, 0);
> +
> +		if (!can_free) {
> +			if (start) {
> +				free_prepared_contig_range(start, i - nr_start);
> +				start = NULL;
> +			}
> +			continue;
> +		}
> +
> +		if (start && memdesc_section(page->flags) != start_sec) {
> +			free_prepared_contig_range(start, i - nr_start);
> +			start = page;
> +			nr_start = i;
> +			start_sec = memdesc_section(page->flags);
> +		} else if (!start) {
> +			start = page;
> +			nr_start = i;
> +			start_sec = memdesc_section(page->flags);
> +		}
> +	}
> +
> +	if (start)
> +		free_prepared_contig_range(start, nr_pages - nr_start);
> +}
> +

Otherwise, LGTM. Thanks.

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

Best Regards,
Yan, Zi

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Vlastimil Babka (SUSE)]

On 3/31/26 17:21, Muhammad Usama Anjum wrote:
> From: Ryan Roberts <ryan.roberts@arm.com>
> 
> Decompose the range of order-0 pages to be freed into the set of largest
> possible power-of-2 size and aligned chunks and free them to the pcp or
> buddy. This improves on the previous approach which freed each order-0
> page individually in a loop. Testing shows performance to be improved by
> more than 10x in some cases.
> 
> Since each page is order-0, we must decrement each page's reference
> count individually and only consider the page for freeing as part of a
> high order chunk if the reference count goes to zero. Additionally
> free_pages_prepare() must be called for each individual order-0 page
> too, so that the struct page state and global accounting state can be
> appropriately managed. But once this is done, the resulting high order
> chunks can be freed as a unit to the pcp or buddy.
> 
> This significantly speeds up the free operation but also has the side
> benefit that high order blocks are added to the pcp instead of each page
> ending up on the pcp order-0 list; memory remains more readily available
> in high orders.
> 
> vmalloc will shortly become a user of this new optimized
> free_contig_range() since it aggressively allocates high order
> non-compound pages, but then calls split_page() to end up with
> contiguous order-0 pages. These can now be freed much more efficiently.
> 
> The execution time of the following function was measured in a server
> class arm64 machine:
> 
> static int page_alloc_high_order_test(void)
> {
> 	unsigned int order = HPAGE_PMD_ORDER;
> 	struct page *page;
> 	int i;
> 
> 	for (i = 0; i < 100000; i++) {
> 		page = alloc_pages(GFP_KERNEL, order);
> 		if (!page)
> 			return -1;
> 		split_page(page, order);
> 		free_contig_range(page_to_pfn(page), 1UL << order);
> 	}
> 
> 	return 0;
> }
> 
> Execution time before: 4097358 usec
> Execution time after:   729831 usec
> 
> Perf trace before:
> 
>     99.63%     0.00%  kthreadd         [kernel.kallsyms]      [.] kthread
>             |
>             ---kthread
>                0xffffb33c12a26af8
>                |
>                |--98.13%--0xffffb33c12a26060
>                |          |
>                |          |--97.37%--free_contig_range
>                |          |          |
>                |          |          |--94.93%--___free_pages
>                |          |          |          |
>                |          |          |          |--55.42%--__free_frozen_pages
>                |          |          |          |          |
>                |          |          |          |           --43.20%--free_frozen_page_commit
>                |          |          |          |                     |
>                |          |          |          |                      --35.37%--_raw_spin_unlock_irqrestore
>                |          |          |          |
>                |          |          |          |--11.53%--_raw_spin_trylock
>                |          |          |          |
>                |          |          |          |--8.19%--__preempt_count_dec_and_test
>                |          |          |          |
>                |          |          |          |--5.64%--_raw_spin_unlock
>                |          |          |          |
>                |          |          |          |--2.37%--__get_pfnblock_flags_mask.isra.0
>                |          |          |          |
>                |          |          |           --1.07%--free_frozen_page_commit
>                |          |          |
>                |          |           --1.54%--__free_frozen_pages
>                |          |
>                |           --0.77%--___free_pages
>                |
>                 --0.98%--0xffffb33c12a26078
>                           alloc_pages_noprof
> 
> Perf trace after:
> 
>      8.42%     2.90%  kthreadd         [kernel.kallsyms]         [k] __free_contig_range
>             |
>             |--5.52%--__free_contig_range
>             |          |
>             |          |--5.00%--free_prepared_contig_range
>             |          |          |
>             |          |          |--1.43%--__free_frozen_pages
>             |          |          |          |
>             |          |          |           --0.51%--free_frozen_page_commit
>             |          |          |
>             |          |          |--1.08%--_raw_spin_trylock
>             |          |          |
>             |          |           --0.89%--_raw_spin_unlock
>             |          |
>             |           --0.52%--free_pages_prepare
>             |
>              --2.90%--ret_from_fork
>                        kthread
>                        0xffffae1c12abeaf8
>                        0xffffae1c12abe7a0
>                        |
>                         --2.69%--vfree
>                                   __free_contig_range
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Nit below:

> @@ -6784,6 +6790,103 @@ void __init page_alloc_sysctl_init(void)
>  	register_sysctl_init("vm", page_alloc_sysctl_table);
>  }
>  
> +static void free_prepared_contig_range(struct page *page,
> +		unsigned long nr_pages)
> +{
> +	while (nr_pages) {
> +		unsigned long pfn = page_to_pfn(page);

Sorry for not noticing earlier. I now realized that because here we are
guaranteed to be restricted to the same section, we can do page_to_pfn()
just once outside the loop and then "pfn += 1UL << order;" below?

> +		unsigned int order;
> +
> +		/* We are limited by the largest buddy order. */
> +		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
> +		/* Don't exceed the number of pages to free. */
> +		order = min_t(unsigned int, order, ilog2(nr_pages));
> +		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
> +
> +		/*
> +		 * Free the chunk as a single block. Our caller has already
> +		 * called free_pages_prepare() for each order-0 page.
> +		 */
> +		__free_frozen_pages(page, order, FPI_PREPARED);
> +
> +		page += 1UL << order;
> +		nr_pages -= 1UL << order;
> +	}
> +}
> +
> +static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
> +		bool is_frozen)
> +{
> +	struct page *page, *start = NULL;
> +	unsigned long nr_start = 0;
> +	unsigned long start_sec;
> +	unsigned long i;
> +
> +	for (i = 0; i < nr_pages; i++) {
> +		bool can_free = true;
> +
> +		/*
> +		 * Contiguous PFNs might not have contiguous "struct pages"
> +		 * in some kernel configs: page++ across a section boundary
> +		 * is undefined. Use pfn_to_page() for each PFN.
> +		 */
> +		page = pfn_to_page(pfn + i);

Hm ideally we'd have some pfn+page iterator thingy that would just do a
page++ on configs where it's contiguous and this more expensive operation
otherwise. Wonder why we don't have it yet. But that's for a possible
followup, not required now.

> +
> +		VM_WARN_ON_ONCE(PageHead(page));
> +		VM_WARN_ON_ONCE(PageTail(page));
> +
> +		if (!is_frozen)
> +			can_free = put_page_testzero(page);
> +
> +		if (can_free)
> +			can_free = free_pages_prepare(page, 0);
> +
> +		if (!can_free) {
> +			if (start) {
> +				free_prepared_contig_range(start, i - nr_start);
> +				start = NULL;
> +			}
> +			continue;
> +		}
> +
> +		if (start && memdesc_section(page->flags) != start_sec) {
> +			free_prepared_contig_range(start, i - nr_start);
> +			start = page;
> +			nr_start = i;
> +			start_sec = memdesc_section(page->flags);
> +		} else if (!start) {
> +			start = page;
> +			nr_start = i;
> +			start_sec = memdesc_section(page->flags);
> +		}
> +	}
> +
> +	if (start)
> +		free_prepared_contig_range(start, nr_pages - nr_start);
> +}
> +

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Muhammad Usama Anjum]

On 31/03/2026 5:09 pm, Zi Yan wrote:
> On 31 Mar 2026, at 11:21, Muhammad Usama Anjum wrote:
> 
>> From: Ryan Roberts <ryan.roberts@arm.com>
>>
>> Decompose the range of order-0 pages to be freed into the set of largest
>> possible power-of-2 size and aligned chunks and free them to the pcp or
>> buddy. This improves on the previous approach which freed each order-0
>> page individually in a loop. Testing shows performance to be improved by
>> more than 10x in some cases.
>>
>> Since each page is order-0, we must decrement each page's reference
>> count individually and only consider the page for freeing as part of a
>> high order chunk if the reference count goes to zero. Additionally
>> free_pages_prepare() must be called for each individual order-0 page
>> too, so that the struct page state and global accounting state can be
>> appropriately managed. But once this is done, the resulting high order
>> chunks can be freed as a unit to the pcp or buddy.
>>
>> This significantly speeds up the free operation but also has the side
>> benefit that high order blocks are added to the pcp instead of each page
>> ending up on the pcp order-0 list; memory remains more readily available
>> in high orders.
>>
>> vmalloc will shortly become a user of this new optimized
>> free_contig_range() since it aggressively allocates high order
>> non-compound pages, but then calls split_page() to end up with
>> contiguous order-0 pages. These can now be freed much more efficiently.
>>
>> The execution time of the following function was measured in a server
>> class arm64 machine:
>>
>> static int page_alloc_high_order_test(void)
>> {
>> 	unsigned int order = HPAGE_PMD_ORDER;
>> 	struct page *page;
>> 	int i;
>>
>> 	for (i = 0; i < 100000; i++) {
>> 		page = alloc_pages(GFP_KERNEL, order);
>> 		if (!page)
>> 			return -1;
>> 		split_page(page, order);
>> 		free_contig_range(page_to_pfn(page), 1UL << order);
>> 	}
>>
>> 	return 0;
>> }
>>
>> Execution time before: 4097358 usec
>> Execution time after:   729831 usec
>>
>> Perf trace before:
>>
>>     99.63%     0.00%  kthreadd         [kernel.kallsyms]      [.] kthread
>>             |
>>             ---kthread
>>                0xffffb33c12a26af8
>>                |
>>                |--98.13%--0xffffb33c12a26060
>>                |          |
>>                |          |--97.37%--free_contig_range
>>                |          |          |
>>                |          |          |--94.93%--___free_pages
>>                |          |          |          |
>>                |          |          |          |--55.42%--__free_frozen_pages
>>                |          |          |          |          |
>>                |          |          |          |           --43.20%--free_frozen_page_commit
>>                |          |          |          |                     |
>>                |          |          |          |                      --35.37%--_raw_spin_unlock_irqrestore
>>                |          |          |          |
>>                |          |          |          |--11.53%--_raw_spin_trylock
>>                |          |          |          |
>>                |          |          |          |--8.19%--__preempt_count_dec_and_test
>>                |          |          |          |
>>                |          |          |          |--5.64%--_raw_spin_unlock
>>                |          |          |          |
>>                |          |          |          |--2.37%--__get_pfnblock_flags_mask.isra.0
>>                |          |          |          |
>>                |          |          |           --1.07%--free_frozen_page_commit
>>                |          |          |
>>                |          |           --1.54%--__free_frozen_pages
>>                |          |
>>                |           --0.77%--___free_pages
>>                |
>>                 --0.98%--0xffffb33c12a26078
>>                           alloc_pages_noprof
>>
>> Perf trace after:
>>
>>      8.42%     2.90%  kthreadd         [kernel.kallsyms]         [k] __free_contig_range
>>             |
>>             |--5.52%--__free_contig_range
>>             |          |
>>             |          |--5.00%--free_prepared_contig_range
>>             |          |          |
>>             |          |          |--1.43%--__free_frozen_pages
>>             |          |          |          |
>>             |          |          |           --0.51%--free_frozen_page_commit
>>             |          |          |
>>             |          |          |--1.08%--_raw_spin_trylock
>>             |          |          |
>>             |          |           --0.89%--_raw_spin_unlock
>>             |          |
>>             |           --0.52%--free_pages_prepare
>>             |
>>              --2.90%--ret_from_fork
>>                        kthread
>>                        0xffffae1c12abeaf8
>>                        0xffffae1c12abe7a0
>>                        |
>>                         --2.69%--vfree
>>                                   __free_contig_range
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
>> ---
>> Changes since v4:
>> - Move can_free initialization inside the loop
>> - Make __free_pages_prepare() static on reviewer's request
>> - Remove export of __free_contig_range
>> - Use pfn_to_page() for each pfn instead of page++
>>
>> Changes since v3:
>> - Move __free_contig_range() to more generic __free_contig_range_common()
>>   which will used to free frozen pages as well
>> - Simplify the loop in __free_contig_range_common()
>> - Rewrite the comment
>>
>> Changes since v2:
>> - Handle different possible section boundries in __free_contig_range()
>> - Drop the TODO
>> - Remove return value from __free_contig_range()
>> - Remove non-functional change from __free_pages_ok()
>>
>> Changes since v1:
>> - Rebase on mm-new
>> - Move FPI_PREPARED check inside __free_pages_prepare() now that
>>   fpi_flags are already being passed.
>> - Add todo (Zi Yan)
>> - Rerun benchmarks
>> - Convert VM_BUG_ON_PAGE() to VM_WARN_ON_ONCE()
>> - Rework order calculation in free_prepared_contig_range() and use
>>   MAX_PAGE_ORDER as high limit instead of pageblock_order as it must
>>   be up to internal __free_frozen_pages() how it frees them
>> ---
>>  include/linux/gfp.h |   2 +
>>  mm/page_alloc.c     | 110 ++++++++++++++++++++++++++++++++++++++++++--
>>  2 files changed, 108 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>> index f82d74a77cad8..7c1f9da7c8e56 100644
>> --- a/include/linux/gfp.h
>> +++ b/include/linux/gfp.h
>> @@ -467,6 +467,8 @@ void free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages);
>>  void free_contig_range(unsigned long pfn, unsigned long nr_pages);
>>  #endif
>>
>> +void __free_contig_range(unsigned long pfn, unsigned long nr_pages);
>> +
>>  DEFINE_FREE(free_page, void *, free_page((unsigned long)_T))
>>
>>  #endif /* __LINUX_GFP_H */
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 75ee81445640b..6e8c79ea62f1c 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -91,6 +91,9 @@ typedef int __bitwise fpi_t;
>>  /* Free the page without taking locks. Rely on trylock only. */
>>  #define FPI_TRYLOCK		((__force fpi_t)BIT(2))
>>
>> +/* free_pages_prepare() has already been called for page(s) being freed. */
>> +#define FPI_PREPARED		((__force fpi_t)BIT(3))
>> +
>>  /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
>>  static DEFINE_MUTEX(pcp_batch_high_lock);
>>  #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
>> @@ -1301,8 +1304,8 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
>>
>>  #endif /* CONFIG_MEM_ALLOC_PROFILING */
>>
>> -__always_inline bool __free_pages_prepare(struct page *page,
>> -					  unsigned int order, fpi_t fpi_flags)
>> +static __always_inline bool __free_pages_prepare(struct page *page,
>> +		unsigned int order, fpi_t fpi_flags)
>>  {
>>  	int bad = 0;
>>  	bool skip_kasan_poison = should_skip_kasan_poison(page);
>> @@ -1310,6 +1313,9 @@ __always_inline bool __free_pages_prepare(struct page *page,
>>  	bool compound = PageCompound(page);
>>  	struct folio *folio = page_folio(page);
>>
>> +	if (fpi_flags & FPI_PREPARED)
>> +		return true;
>> +
>>  	VM_BUG_ON_PAGE(PageTail(page), page);
>>
>>  	trace_mm_page_free(page, order);
>> @@ -6784,6 +6790,103 @@ void __init page_alloc_sysctl_init(void)
>>  	register_sysctl_init("vm", page_alloc_sysctl_table);
>>  }
>>
>> +static void free_prepared_contig_range(struct page *page,
>> +		unsigned long nr_pages)
>> +{
>> +	while (nr_pages) {
>> +		unsigned long pfn = page_to_pfn(page);
> 
> pfn does not change after this assignment. That is why David suggested
> prefixing a const. You can send a fixup to this patch to change this
> if there is no substantial change needed for this series.
I'm going to move page_to_pfn() out of this loop as now its guaranteed
that they are from the same section. The page++ would be safe here.

> 
>> +		unsigned int order;
>> +
>> +		/* We are limited by the largest buddy order. */
>> +		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
>> +		/* Don't exceed the number of pages to free. */
>> +		order = min_t(unsigned int, order, ilog2(nr_pages));
>> +		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
>> +
>> +		/*
>> +		 * Free the chunk as a single block. Our caller has already
>> +		 * called free_pages_prepare() for each order-0 page.
>> +		 */
>> +		__free_frozen_pages(page, order, FPI_PREPARED);
>> +
>> +		page += 1UL << order;
>> +		nr_pages -= 1UL << order;
>> +	}
>> +}
>> +
>> +static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
>> +		bool is_frozen)
>> +{
>> +	struct page *page, *start = NULL;
>> +	unsigned long nr_start = 0;
>> +	unsigned long start_sec;
>> +	unsigned long i;
>> +
>> +	for (i = 0; i < nr_pages; i++) {
>> +		bool can_free = true;
>> +
>> +		/*
>> +		 * Contiguous PFNs might not have contiguous "struct pages"
>> +		 * in some kernel configs: page++ across a section boundary
>> +		 * is undefined. Use pfn_to_page() for each PFN.
>> +		 */
>> +		page = pfn_to_page(pfn + i);
> 
> page is local to this loop. You probably can move its declaration here.
> But feel free to ignore this suggestion.
I'll make this change.

> 
> I was about to suggest make it const, but put_page_test_zero()
> and free_pages_prepare() do not accept const struct page yet.
> 
>> +
>> +		VM_WARN_ON_ONCE(PageHead(page));
>> +		VM_WARN_ON_ONCE(PageTail(page));
>> +
>> +		if (!is_frozen)
>> +			can_free = put_page_testzero(page);
>> +
>> +		if (can_free)
>> +			can_free = free_pages_prepare(page, 0);
>> +
>> +		if (!can_free) {
>> +			if (start) {
>> +				free_prepared_contig_range(start, i - nr_start);
>> +				start = NULL;
>> +			}
>> +			continue;
>> +		}
>> +
>> +		if (start && memdesc_section(page->flags) != start_sec) {
>> +			free_prepared_contig_range(start, i - nr_start);
>> +			start = page;
>> +			nr_start = i;
>> +			start_sec = memdesc_section(page->flags);
>> +		} else if (!start) {
>> +			start = page;
>> +			nr_start = i;
>> +			start_sec = memdesc_section(page->flags);
>> +		}
>> +	}
>> +
>> +	if (start)
>> +		free_prepared_contig_range(start, nr_pages - nr_start);
>> +}
>> +
> 
> Otherwise, LGTM. Thanks.
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>
Thank you so much!

> 
> Best Regards,
> Yan, Zi

-- 
---
Thanks,
Usama

Re: [PATCH v5 2/3] vmalloc: Optimize vfree

[Vlastimil Babka (SUSE)]

Nit: the subject could be more specific, e.g. like this?

vmalloc: Optimize vfree with free_pages_bulk()

On 3/31/26 17:22, Muhammad Usama Anjum wrote:
> From: Ryan Roberts <ryan.roberts@arm.com>
> 
> Whenever vmalloc allocates high order pages (e.g. for a huge mapping) it
> must immediately split_page() to order-0 so that it remains compatible
> with users that want to access the underlying struct page.
> Commit a06157804399 ("mm/vmalloc: request large order pages from buddy
> allocator") recently made it much more likely for vmalloc to allocate
> high order pages which are subsequently split to order-0.
> 
> Unfortunately this had the side effect of causing performance
> regressions for tight vmalloc/vfree loops (e.g. test_vmalloc.ko
> benchmarks). See Closes: tag. This happens because the high order pages
> must be gotten from the buddy but then because they are split to
> order-0, when they are freed they are freed to the order-0 pcp.
> Previously allocation was for order-0 pages so they were recycled from
> the pcp.
> 
> It would be preferable if when vmalloc allocates an (e.g.) order-3 page
> that it also frees that order-3 page to the order-3 pcp, then the
> regression could be removed.
> 
> So let's do exactly that; update stats separately first as coalescing is
> hard to do correctly without complexity. Use free_pages_bulk() which uses
> the new __free_contig_range() API to batch-free contiguous ranges of pfns.
> This not only removes the regression, but significantly improves
> performance of vfree beyond the baseline.
> 
> A selection of test_vmalloc benchmarks running on arm64 server class
> system. mm-new is the baseline. Commit a06157804399 ("mm/vmalloc: request
> large order pages from buddy allocator") was added in v6.19-rc1 where we
> see regressions. Then with this change performance is much better. (>0
> is faster, <0 is slower, (R)/(I) = statistically significant
> Regression/Improvement):
> 
> +-----------------+----------------------------------------------------------+-------------------+--------------------+
> | Benchmark       | Result Class                                             |   mm-new          |  this series       |
> +=================+==========================================================+===================+====================+
> | micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |        1331843.33 |         (I) 67.17% |
> |                 | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |         415907.33 |             -5.14% |
> |                 | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |         755448.00 |         (I) 53.55% |
> |                 | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |        1591331.33 |         (I) 57.26% |
> |                 | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |        1594345.67 |         (I) 68.46% |
> |                 | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |        1071826.00 |         (I) 79.27% |
> |                 | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |        1018385.00 |         (I) 84.17% |
> |                 | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |        3970899.67 |         (I) 77.01% |
> |                 | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |        3821788.67 |         (I) 89.44% |
> |                 | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |        7795968.00 |         (I) 82.67% |
> |                 | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |        6530169.67 |        (I) 118.09% |
> |                 | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |         626808.33 |             -0.98% |
> |                 | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         532145.67 |             -1.68% |
> |                 | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         537032.67 |             -0.96% |
> |                 | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |        8805069.00 |         (I) 74.58% |
> |                 | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |         500824.67 |              4.35% |
> |                 | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |        1637554.67 |         (I) 76.99% |
> |                 | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |        4556288.67 |         (I) 72.23% |
> |                 | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |         107371.00 |             -0.70% |
> +-----------------+----------------------------------------------------------+-------------------+--------------------+
> 
> Fixes: a06157804399 ("mm/vmalloc: request large order pages from buddy allocator")
> Closes: https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com/
> Acked-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

> +void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
> +{
> +	while (nr_pages) {
> +		unsigned long nr_contig = num_pages_contiguous(page_array, nr_pages);
> +
> +		__free_contig_range(page_to_pfn(*page_array), nr_contig);

I'll note that num_pages_contiguous() already handled crossing the section
boundaries and __free_contig_range() checks them again. But that's fine I
think, we don't have to optimize for !SPARSEMEM_VMEMMAP architectures and on
SPARSEMEM_VMEMMAP the checks should be compiled out, right.
It would complicate the API otherwise.

> +
> +		nr_pages -= nr_contig;
> +		page_array += nr_contig;
> +		cond_resched();
> +	}
> +}
> +
>  /*
>   * This is the 'heart' of the zoned buddy allocator.
>   */

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Muhammad Usama Anjum]

Hi,

Thank you for the suggestion. I think I'll send the updated
series today as I don't see any outstanding item now.

On 01/04/2026 10:07 am, Vlastimil Babka (SUSE) wrote:
> On 3/31/26 17:21, Muhammad Usama Anjum wrote:
>> From: Ryan Roberts <ryan.roberts@arm.com>
>>
>> Decompose the range of order-0 pages to be freed into the set of largest
>> possible power-of-2 size and aligned chunks and free them to the pcp or
>> buddy. This improves on the previous approach which freed each order-0
>> page individually in a loop. Testing shows performance to be improved by
>> more than 10x in some cases.
>>
>> Since each page is order-0, we must decrement each page's reference
>> count individually and only consider the page for freeing as part of a
>> high order chunk if the reference count goes to zero. Additionally
>> free_pages_prepare() must be called for each individual order-0 page
>> too, so that the struct page state and global accounting state can be
>> appropriately managed. But once this is done, the resulting high order
>> chunks can be freed as a unit to the pcp or buddy.
>>
>> This significantly speeds up the free operation but also has the side
>> benefit that high order blocks are added to the pcp instead of each page
>> ending up on the pcp order-0 list; memory remains more readily available
>> in high orders.
>>
>> vmalloc will shortly become a user of this new optimized
>> free_contig_range() since it aggressively allocates high order
>> non-compound pages, but then calls split_page() to end up with
>> contiguous order-0 pages. These can now be freed much more efficiently.
>>
>> The execution time of the following function was measured in a server
>> class arm64 machine:
>>
>> static int page_alloc_high_order_test(void)
>> {
>> 	unsigned int order = HPAGE_PMD_ORDER;
>> 	struct page *page;
>> 	int i;
>>
>> 	for (i = 0; i < 100000; i++) {
>> 		page = alloc_pages(GFP_KERNEL, order);
>> 		if (!page)
>> 			return -1;
>> 		split_page(page, order);
>> 		free_contig_range(page_to_pfn(page), 1UL << order);
>> 	}
>>
>> 	return 0;
>> }
>>
>> Execution time before: 4097358 usec
>> Execution time after:   729831 usec
>>
>> Perf trace before:
>>
>>     99.63%     0.00%  kthreadd         [kernel.kallsyms]      [.] kthread
>>             |
>>             ---kthread
>>                0xffffb33c12a26af8
>>                |
>>                |--98.13%--0xffffb33c12a26060
>>                |          |
>>                |          |--97.37%--free_contig_range
>>                |          |          |
>>                |          |          |--94.93%--___free_pages
>>                |          |          |          |
>>                |          |          |          |--55.42%--__free_frozen_pages
>>                |          |          |          |          |
>>                |          |          |          |           --43.20%--free_frozen_page_commit
>>                |          |          |          |                     |
>>                |          |          |          |                      --35.37%--_raw_spin_unlock_irqrestore
>>                |          |          |          |
>>                |          |          |          |--11.53%--_raw_spin_trylock
>>                |          |          |          |
>>                |          |          |          |--8.19%--__preempt_count_dec_and_test
>>                |          |          |          |
>>                |          |          |          |--5.64%--_raw_spin_unlock
>>                |          |          |          |
>>                |          |          |          |--2.37%--__get_pfnblock_flags_mask.isra.0
>>                |          |          |          |
>>                |          |          |           --1.07%--free_frozen_page_commit
>>                |          |          |
>>                |          |           --1.54%--__free_frozen_pages
>>                |          |
>>                |           --0.77%--___free_pages
>>                |
>>                 --0.98%--0xffffb33c12a26078
>>                           alloc_pages_noprof
>>
>> Perf trace after:
>>
>>      8.42%     2.90%  kthreadd         [kernel.kallsyms]         [k] __free_contig_range
>>             |
>>             |--5.52%--__free_contig_range
>>             |          |
>>             |          |--5.00%--free_prepared_contig_range
>>             |          |          |
>>             |          |          |--1.43%--__free_frozen_pages
>>             |          |          |          |
>>             |          |          |           --0.51%--free_frozen_page_commit
>>             |          |          |
>>             |          |          |--1.08%--_raw_spin_trylock
>>             |          |          |
>>             |          |           --0.89%--_raw_spin_unlock
>>             |          |
>>             |           --0.52%--free_pages_prepare
>>             |
>>              --2.90%--ret_from_fork
>>                        kthread
>>                        0xffffae1c12abeaf8
>>                        0xffffae1c12abe7a0
>>                        |
>>                         --2.69%--vfree
>>                                   __free_contig_range
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> 
> Nit below:
> 
>> @@ -6784,6 +6790,103 @@ void __init page_alloc_sysctl_init(void)
>>  	register_sysctl_init("vm", page_alloc_sysctl_table);
>>  }
>>  
>> +static void free_prepared_contig_range(struct page *page,
>> +		unsigned long nr_pages)
>> +{
>> +	while (nr_pages) {
>> +		unsigned long pfn = page_to_pfn(page);
> 
> Sorry for not noticing earlier. I now realized that because here we are
> guaranteed to be restricted to the same section, we can do page_to_pfn()
> just once outside the loop and then "pfn += 1UL << order;" below?
Please let me make this update.

> 
>> +		unsigned int order;
>> +
>> +		/* We are limited by the largest buddy order. */
>> +		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
>> +		/* Don't exceed the number of pages to free. */
>> +		order = min_t(unsigned int, order, ilog2(nr_pages));
>> +		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
>> +
>> +		/*
>> +		 * Free the chunk as a single block. Our caller has already
>> +		 * called free_pages_prepare() for each order-0 page.
>> +		 */
>> +		__free_frozen_pages(page, order, FPI_PREPARED);
>> +
>> +		page += 1UL << order;
>> +		nr_pages -= 1UL << order;
>> +	}
>> +}
>> +
>> +static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
>> +		bool is_frozen)
>> +{
>> +	struct page *page, *start = NULL;
>> +	unsigned long nr_start = 0;
>> +	unsigned long start_sec;
>> +	unsigned long i;
>> +
>> +	for (i = 0; i < nr_pages; i++) {
>> +		bool can_free = true;
>> +
>> +		/*
>> +		 * Contiguous PFNs might not have contiguous "struct pages"
>> +		 * in some kernel configs: page++ across a section boundary
>> +		 * is undefined. Use pfn_to_page() for each PFN.
>> +		 */
>> +		page = pfn_to_page(pfn + i);
> 
> Hm ideally we'd have some pfn+page iterator thingy that would just do a
> page++ on configs where it's contiguous and this more expensive operation
> otherwise. Wonder why we don't have it yet. But that's for a possible
> followup, not required now.
Yeah, it'll be useful and will make the code overall simple to follow.

> 
>> +
>> +		VM_WARN_ON_ONCE(PageHead(page));
>> +		VM_WARN_ON_ONCE(PageTail(page));
>> +
>> +		if (!is_frozen)
>> +			can_free = put_page_testzero(page);
>> +
>> +		if (can_free)
>> +			can_free = free_pages_prepare(page, 0);
>> +
>> +		if (!can_free) {
>> +			if (start) {
>> +				free_prepared_contig_range(start, i - nr_start);
>> +				start = NULL;
>> +			}
>> +			continue;
>> +		}
>> +
>> +		if (start && memdesc_section(page->flags) != start_sec) {
>> +			free_prepared_contig_range(start, i - nr_start);
>> +			start = page;
>> +			nr_start = i;
>> +			start_sec = memdesc_section(page->flags);
>> +		} else if (!start) {
>> +			start = page;
>> +			nr_start = i;
>> +			start_sec = memdesc_section(page->flags);
>> +		}
>> +	}
>> +
>> +	if (start)
>> +		free_prepared_contig_range(start, nr_pages - nr_start);
>> +}
>> +
> 
> 

-- 
---
Thanks,
Usama

Re: [PATCH v5 2/3] vmalloc: Optimize vfree

[David Hildenbrand (Arm)]

On 4/1/26 11:19, Vlastimil Babka (SUSE) wrote:
> 
> Nit: the subject could be more specific, e.g. like this?
> 
> vmalloc: Optimize vfree with free_pages_bulk()
> 
> On 3/31/26 17:22, Muhammad Usama Anjum wrote:
>> From: Ryan Roberts <ryan.roberts@arm.com>
>>
>> Whenever vmalloc allocates high order pages (e.g. for a huge mapping) it
>> must immediately split_page() to order-0 so that it remains compatible
>> with users that want to access the underlying struct page.
>> Commit a06157804399 ("mm/vmalloc: request large order pages from buddy
>> allocator") recently made it much more likely for vmalloc to allocate
>> high order pages which are subsequently split to order-0.
>>
>> Unfortunately this had the side effect of causing performance
>> regressions for tight vmalloc/vfree loops (e.g. test_vmalloc.ko
>> benchmarks). See Closes: tag. This happens because the high order pages
>> must be gotten from the buddy but then because they are split to
>> order-0, when they are freed they are freed to the order-0 pcp.
>> Previously allocation was for order-0 pages so they were recycled from
>> the pcp.
>>
>> It would be preferable if when vmalloc allocates an (e.g.) order-3 page
>> that it also frees that order-3 page to the order-3 pcp, then the
>> regression could be removed.
>>
>> So let's do exactly that; update stats separately first as coalescing is
>> hard to do correctly without complexity. Use free_pages_bulk() which uses
>> the new __free_contig_range() API to batch-free contiguous ranges of pfns.
>> This not only removes the regression, but significantly improves
>> performance of vfree beyond the baseline.
>>
>> A selection of test_vmalloc benchmarks running on arm64 server class
>> system. mm-new is the baseline. Commit a06157804399 ("mm/vmalloc: request
>> large order pages from buddy allocator") was added in v6.19-rc1 where we
>> see regressions. Then with this change performance is much better. (>0
>> is faster, <0 is slower, (R)/(I) = statistically significant
>> Regression/Improvement):
>>
>> +-----------------+----------------------------------------------------------+-------------------+--------------------+
>> | Benchmark       | Result Class                                             |   mm-new          |  this series       |
>> +=================+==========================================================+===================+====================+
>> | micromm/vmalloc | fix_align_alloc_test: p:1, h:0, l:500000 (usec)          |        1331843.33 |         (I) 67.17% |
>> |                 | fix_size_alloc_test: p:1, h:0, l:500000 (usec)           |         415907.33 |             -5.14% |
>> |                 | fix_size_alloc_test: p:4, h:0, l:500000 (usec)           |         755448.00 |         (I) 53.55% |
>> |                 | fix_size_alloc_test: p:16, h:0, l:500000 (usec)          |        1591331.33 |         (I) 57.26% |
>> |                 | fix_size_alloc_test: p:16, h:1, l:500000 (usec)          |        1594345.67 |         (I) 68.46% |
>> |                 | fix_size_alloc_test: p:64, h:0, l:100000 (usec)          |        1071826.00 |         (I) 79.27% |
>> |                 | fix_size_alloc_test: p:64, h:1, l:100000 (usec)          |        1018385.00 |         (I) 84.17% |
>> |                 | fix_size_alloc_test: p:256, h:0, l:100000 (usec)         |        3970899.67 |         (I) 77.01% |
>> |                 | fix_size_alloc_test: p:256, h:1, l:100000 (usec)         |        3821788.67 |         (I) 89.44% |
>> |                 | fix_size_alloc_test: p:512, h:0, l:100000 (usec)         |        7795968.00 |         (I) 82.67% |
>> |                 | fix_size_alloc_test: p:512, h:1, l:100000 (usec)         |        6530169.67 |        (I) 118.09% |
>> |                 | full_fit_alloc_test: p:1, h:0, l:500000 (usec)           |         626808.33 |             -0.98% |
>> |                 | kvfree_rcu_1_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         532145.67 |             -1.68% |
>> |                 | kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec) |         537032.67 |             -0.96% |
>> |                 | long_busy_list_alloc_test: p:1, h:0, l:500000 (usec)     |        8805069.00 |         (I) 74.58% |
>> |                 | pcpu_alloc_test: p:1, h:0, l:500000 (usec)               |         500824.67 |              4.35% |
>> |                 | random_size_align_alloc_test: p:1, h:0, l:500000 (usec)  |        1637554.67 |         (I) 76.99% |
>> |                 | random_size_alloc_test: p:1, h:0, l:500000 (usec)        |        4556288.67 |         (I) 72.23% |
>> |                 | vm_map_ram_test: p:1, h:0, l:500000 (usec)               |         107371.00 |             -0.70% |
>> +-----------------+----------------------------------------------------------+-------------------+--------------------+
>>
>> Fixes: a06157804399 ("mm/vmalloc: request large order pages from buddy allocator")
>> Closes: https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com/
>> Acked-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> Co-developed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> 
>> +void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
>> +{
>> +	while (nr_pages) {
>> +		unsigned long nr_contig = num_pages_contiguous(page_array, nr_pages);
>> +
>> +		__free_contig_range(page_to_pfn(*page_array), nr_contig);
> 
> I'll note that num_pages_contiguous() already handled crossing the section
> boundaries and __free_contig_range() checks them again. But that's fine I
> think, we don't have to optimize for !SPARSEMEM_VMEMMAP architectures and on
> SPARSEMEM_VMEMMAP the checks should be compiled out, right.

Yes, that was my reasoning.

Note that we could have

(a) Contiguous PFN ranges with a non-contiguous memmap

(b) Contiguous memmap with non-contiguous PFN range


So for an external interface that consumes pfns (free_contig_range()) we
must check (a), for an external interface that consumes pages
(free_pages_bulk()) we must check (b).

As free_pages_bulk() uses the same internal as free_contig_range(), it
will not only check (b), but also (a).

So we cannot just optimize out either but would need a separate function
for free_pages_bulk() to call.

Not worth it :)

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[David Hildenbrand (Arm)]

>> +static void free_prepared_contig_range(struct page *page,
>> +		unsigned long nr_pages)
>> +{
>> +	while (nr_pages) {
>> +		unsigned long pfn = page_to_pfn(page);
> 
> Sorry for not noticing earlier. I now realized that because here we are
> guaranteed to be restricted to the same section, we can do page_to_pfn()
> just once outside the loop and then "pfn += 1UL << order;" below?

+1

> 
>> +		unsigned int order;
>> +
>> +		/* We are limited by the largest buddy order. */
>> +		order = pfn ? __ffs(pfn) : MAX_PAGE_ORDER;
>> +		/* Don't exceed the number of pages to free. */
>> +		order = min_t(unsigned int, order, ilog2(nr_pages));
>> +		order = min_t(unsigned int, order, MAX_PAGE_ORDER);
>> +
>> +		/*
>> +		 * Free the chunk as a single block. Our caller has already
>> +		 * called free_pages_prepare() for each order-0 page.
>> +		 */
>> +		__free_frozen_pages(page, order, FPI_PREPARED);
>> +
>> +		page += 1UL << order;
>> +		nr_pages -= 1UL << order;
>> +	}
>> +}
>> +
>> +static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
>> +		bool is_frozen)
>> +{
>> +	struct page *page, *start = NULL;
>> +	unsigned long nr_start = 0;
>> +	unsigned long start_sec;
>> +	unsigned long i;
>> +
>> +	for (i = 0; i < nr_pages; i++) {
>> +		bool can_free = true;
>> +
>> +		/*
>> +		 * Contiguous PFNs might not have contiguous "struct pages"
>> +		 * in some kernel configs: page++ across a section boundary
>> +		 * is undefined. Use pfn_to_page() for each PFN.
>> +		 */
>> +		page = pfn_to_page(pfn + i);
> 
> Hm ideally we'd have some pfn+page iterator thingy that would just do a
> page++ on configs where it's contiguous and this more expensive operation
> otherwise. Wonder why we don't have it yet. But that's for a possible
> followup, not required now.

pfn_to_page() is on relevant configs close to just a "page + i". Not
entirely, but I am not sure if the micro-gain would really be worth it.

E.g., on CONFIG_SPARSEMEM_VMEMMAP

#define __pfn_to_page(pfn)	vmemmap + (pfn)


Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v5 1/3] mm/page_alloc: Optimize free_contig_range()

[Vlastimil Babka (SUSE)]

On 4/1/26 11:59, David Hildenbrand (Arm) wrote:
>>> +
>>> +	for (i = 0; i < nr_pages; i++) {
>>> +		bool can_free = true;
>>> +
>>> +		/*
>>> +		 * Contiguous PFNs might not have contiguous "struct pages"
>>> +		 * in some kernel configs: page++ across a section boundary
>>> +		 * is undefined. Use pfn_to_page() for each PFN.
>>> +		 */
>>> +		page = pfn_to_page(pfn + i);
>> 
>> Hm ideally we'd have some pfn+page iterator thingy that would just do a
>> page++ on configs where it's contiguous and this more expensive operation
>> otherwise. Wonder why we don't have it yet. But that's for a possible
>> followup, not required now.
> 
> pfn_to_page() is on relevant configs close to just a "page + i". Not
> entirely, but I am not sure if the micro-gain would really be worth it.
> 
> E.g., on CONFIG_SPARSEMEM_VMEMMAP
> 
> #define __pfn_to_page(pfn)	vmemmap + (pfn)

Oh I see. Yeah agree not worth it. The compiler can probably turn it to
page++ already then.

> 
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
>