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 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 | 38 ++++++++++++++++++++++++++++++++++++++
mm/vmalloc.c | 16 +++++-----------
3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5175,6 +5175,44 @@ 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)
+{
+ unsigned long start_pfn = 0, pfn;
+ unsigned long i, nr_contig = 0;
+
+ for (i = 0; i < nr_pages; i++) {
+ pfn = page_to_pfn(page_array[i]);
+ if (!nr_contig) {
+ start_pfn = pfn;
+ nr_contig = 1;
+ } else if (start_pfn + nr_contig != pfn) {
+ __free_contig_range(start_pfn, nr_contig);
+ start_pfn = pfn;
+ nr_contig = 1;
+ cond_resched();
+ } else {
+ nr_contig++;
+ }
+ }
+ if (nr_contig)
+ __free_contig_range(start_pfn, nr_contig);
+}
+
/*
* 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);
}
--
2.47.3On 3/27/26 13:57, 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>
On 30/03/2026 3:35 pm, Vlastimil Babka (SUSE) wrote:
> On 3/27/26 13:57, 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>
Thank you. But as the implementation of free_pages_bulk() has
changed to using num_pages_contiguous(), I cannot take this tag.
Please review the next version again.
>
>
--
---
Thanks,
Usama
On 3/27/26 13:57, 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>
> ---
> 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 | 38 ++++++++++++++++++++++++++++++++++++++
> mm/vmalloc.c | 16 +++++-----------
> 3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5175,6 +5175,44 @@ 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)
> +{
> + unsigned long start_pfn = 0, pfn;
> + unsigned long i, nr_contig = 0;
> +
> + for (i = 0; i < nr_pages; i++) {
> + pfn = page_to_pfn(page_array[i]);
> + if (!nr_contig) {
> + start_pfn = pfn;
> + nr_contig = 1;
> + } else if (start_pfn + nr_contig != pfn) {
> + __free_contig_range(start_pfn, nr_contig);
> + start_pfn = pfn;
> + nr_contig = 1;
> + cond_resched();
> + } else {
> + nr_contig++;
> + }
> + }
What happened to the idea of using num_pages_contiguous()? I think that
should generate more efficient code (all we're doing is comparing
pointers really on SPARSEMEM_VMEMMAP) and the end result looks more
readable?
--
Cheers,
David
On 30/03/2026 3:38 pm, David Hildenbrand (Arm) wrote:
> On 3/27/26 13:57, 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>
>> ---
>> 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 | 38 ++++++++++++++++++++++++++++++++++++++
>> mm/vmalloc.c | 16 +++++-----------
>> 3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5175,6 +5175,44 @@ 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)
>> +{
>> + unsigned long start_pfn = 0, pfn;
>> + unsigned long i, nr_contig = 0;
>> +
>> + for (i = 0; i < nr_pages; i++) {
>> + pfn = page_to_pfn(page_array[i]);
>> + if (!nr_contig) {
>> + start_pfn = pfn;
>> + nr_contig = 1;
>> + } else if (start_pfn + nr_contig != pfn) {
>> + __free_contig_range(start_pfn, nr_contig);
>> + start_pfn = pfn;
>> + nr_contig = 1;
>> + cond_resched();
>> + } else {
>> + nr_contig++;
>> + }
>> + }
>
> What happened to the idea of using num_pages_contiguous()? I think that
> should generate more efficient code (all we're doing is comparing
> pointers really on SPARSEMEM_VMEMMAP) and the end result looks more
> readable?
Sorry, I misunderstood you in the light of duplicate usage of
num_pages_contiguous(). I'll update the implementation.
Copying from previous thread.
>>> Could we use num_pages_contiguous() here?
>>>
>>> while (nr_pages) {
>>> unsigned long nr_contig_pages = num_pages_contiguous(page_array, nr_pages);
>>>
>>> __free_contig_range(pfn_to_page(*page_array), nr_contig_pages);
>>>
>>> nr_pages -= nr_contig;
>>> page_array += nr_contig;
>>> cond_resched();
>>> }
>>>
>>> Something like that?
>> __free_contig_range() is already checking for the sections. If
>> num_pages_contiguous() is called here, it'll cause the duplication
>> of the section check.
> No problem. For configs we care about it's optimized out entirely either
> way.
Thanks,
Usama
On 3/30/26 18:15, Muhammad Usama Anjum wrote:
> On 30/03/2026 3:38 pm, David Hildenbrand (Arm) wrote:
>> On 3/27/26 13:57, 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>
>>> ---
>>> 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 | 38 ++++++++++++++++++++++++++++++++++++++
>>> mm/vmalloc.c | 16 +++++-----------
>>> 3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5175,6 +5175,44 @@ 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)
>>> +{
>>> + unsigned long start_pfn = 0, pfn;
>>> + unsigned long i, nr_contig = 0;
>>> +
>>> + for (i = 0; i < nr_pages; i++) {
>>> + pfn = page_to_pfn(page_array[i]);
>>> + if (!nr_contig) {
>>> + start_pfn = pfn;
>>> + nr_contig = 1;
>>> + } else if (start_pfn + nr_contig != pfn) {
>>> + __free_contig_range(start_pfn, nr_contig);
>>> + start_pfn = pfn;
>>> + nr_contig = 1;
>>> + cond_resched();
>>> + } else {
>>> + nr_contig++;
>>> + }
>>> + }
>>
>> What happened to the idea of using num_pages_contiguous()? I think that
>> should generate more efficient code (all we're doing is comparing
>> pointers really on SPARSEMEM_VMEMMAP) and the end result looks more
>> readable?
> Sorry, I misunderstood you in the light of duplicate usage of
> num_pages_contiguous(). I'll update the implementation.
A note that it should even speedup SPARSEMEM && !SPARSEMEM_VMEMMAP,
where a page_to_pfn() is expensive and best minimized/avoided :)
--
Cheers,
David
On Fri, Mar 27, 2026 at 12:57:14PM +0000, 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>
> ---
> 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 | 38 ++++++++++++++++++++++++++++++++++++++
> mm/vmalloc.c | 16 +++++-----------
> 3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5175,6 +5175,44 @@ 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)
> +{
> + unsigned long start_pfn = 0, pfn;
> + unsigned long i, nr_contig = 0;
> +
> + for (i = 0; i < nr_pages; i++) {
> + pfn = page_to_pfn(page_array[i]);
> + if (!nr_contig) {
> + start_pfn = pfn;
> + nr_contig = 1;
> + } else if (start_pfn + nr_contig != pfn) {
> + __free_contig_range(start_pfn, nr_contig);
> + start_pfn = pfn;
> + nr_contig = 1;
> + cond_resched();
> + } else {
> + nr_contig++;
> + }
> + }
> + if (nr_contig)
> + __free_contig_range(start_pfn, nr_contig);
> +}
> +
> /*
> * 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
>
LGTM:
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
--
Uladzislau Rezki
On 30/03/2026 1:30 pm, Uladzislau Rezki wrote:
> On Fri, Mar 27, 2026 at 12:57:14PM +0000, 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>
>> ---
>> 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 | 38 ++++++++++++++++++++++++++++++++++++++
>> mm/vmalloc.c | 16 +++++-----------
>> 3 files changed, 45 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 18a96b51aa0be..64be8a9019dca 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5175,6 +5175,44 @@ 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)
>> +{
>> + unsigned long start_pfn = 0, pfn;
>> + unsigned long i, nr_contig = 0;
>> +
>> + for (i = 0; i < nr_pages; i++) {
>> + pfn = page_to_pfn(page_array[i]);
>> + if (!nr_contig) {
>> + start_pfn = pfn;
>> + nr_contig = 1;
>> + } else if (start_pfn + nr_contig != pfn) {
>> + __free_contig_range(start_pfn, nr_contig);
>> + start_pfn = pfn;
>> + nr_contig = 1;
>> + cond_resched();
>> + } else {
>> + nr_contig++;
>> + }
>> + }
>> + if (nr_contig)
>> + __free_contig_range(start_pfn, nr_contig);
>> +}
>> +
>> /*
>> * 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
>>
> LGTM:
>
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Thank you. But as the implementation of free_pages_bulk() has
changed to using num_pages_contiguous(), I cannot take this tag.
>
> --
> Uladzislau Rezki
--
---
Thanks,
Usama
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