[PATCH v2 1/2] mm/vmalloc: Switch to bulk allocator in __vmalloc_area_node()

Uladzislau Rezki (Sony)
2021-05-09T19:39:01Z

Recently there has been introduced a page bulk allocator for
users which need to get number of pages per one call request.

For order-0 pages switch to __alloc_pages_bulk() instead of
alloc_pages_node(), the reason is the former is not capable
of allocating set of pages, thus a one call is per one page.

Second, according to my tests the bulk allocator uses less
cycles even for scenarios when only one page is requested.
Running the "perf" on same test case shows below difference:

<default>
- 45.18% __vmalloc_node
- __vmalloc_node_range
- 35.60% __alloc_pages
- get_page_from_freelist
3.36% __list_del_entry_valid
3.00% check_preemption_disabled
1.42% prep_new_page
<default>

<patch>
- 31.00% __vmalloc_node
- __vmalloc_node_range
- 14.48% __alloc_pages_bulk
3.22% __list_del_entry_valid
- 0.83% __alloc_pages
get_page_from_freelist
<patch>

The "test_vmalloc.sh" also shows performance improvements:

fix_size_alloc_test_4MB loops: 1000000 avg: 89105095 usec
fix_size_alloc_test loops: 1000000 avg: 513672 usec
full_fit_alloc_test loops: 1000000 avg: 748900 usec
long_busy_list_alloc_test loops: 1000000 avg: 8043038 usec
random_size_alloc_test loops: 1000000 avg: 4028582 usec
fix_align_alloc_test loops: 1000000 avg: 1457671 usec

fix_size_alloc_test_4MB loops: 1000000 avg: 62083711 usec
fix_size_alloc_test loops: 1000000 avg: 449207 usec
full_fit_alloc_test loops: 1000000 avg: 735985 usec
long_busy_list_alloc_test loops: 1000000 avg: 5176052 usec
random_size_alloc_test loops: 1000000 avg: 2589252 usec
fix_align_alloc_test loops: 1000000 avg: 1365009 usec

For example 4MB allocations illustrates ~30% gain, all the
rest is also better.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 74 ++++++++++++++++++++++++++++------------------------
1 file changed, 40 insertions(+), 34 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5d96fee17226..dbc6744400d5 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2766,8 +2766,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
unsigned long array_size;
unsigned int nr_small_pages = size >> PAGE_SHIFT;
unsigned int page_order;
- struct page **pages;
- unsigned int i;

array_size = (unsigned long)nr_small_pages * sizeof(struct page *);
gfp_mask |= __GFP_NOWARN;
@@ -2776,13 +2774,13 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,

/* Please note that the recursion is strictly bounded. */
if (array_size > PAGE_SIZE) {
- pages = __vmalloc_node(array_size, 1, nested_gfp, node,
+ area->pages = __vmalloc_node(array_size, 1, nested_gfp, node,
area->caller);
} else {
- pages = kmalloc_node(array_size, nested_gfp, node);
+ area->pages = kmalloc_node(array_size, nested_gfp, node);
}

- if (!pages) {
+ if (!area->pages) {
free_vm_area(area);
warn_alloc(gfp_mask, NULL,
"vmalloc size %lu allocation failure: "
@@ -2791,43 +2789,51 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
return NULL;
}

- area->pages = pages;
- area->nr_pages = nr_small_pages;
set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
-
page_order = vm_area_page_order(area);

- /*
- * Careful, we allocate and map page_order pages, but tracking is done
- * per PAGE_SIZE page so as to keep the vm_struct APIs independent of
- * the physical/mapped size.
- */
- for (i = 0; i < area->nr_pages; i += 1U << page_order) {
- struct page *page;
- int p;
-
- /* Compound pages required for remap_vmalloc_page */
- page = alloc_pages_node(node, gfp_mask | __GFP_COMP, page_order);
- if (unlikely(!page)) {
- /* Successfully allocated i pages, free them in __vfree() */
- area->nr_pages = i;
- atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
- warn_alloc(gfp_mask, NULL,
- "vmalloc size %lu allocation failure: "
- "page order %u allocation failed",
- area->nr_pages * PAGE_SIZE, page_order);
- goto fail;
- }
+ if (!page_order) {
+ area->nr_pages = __alloc_pages_bulk(gfp_mask, node,
+ NULL, nr_small_pages, NULL, area->pages);
+ } else {
+ /*
+ * Careful, we allocate and map page_order pages, but tracking is done
+ * per PAGE_SIZE page so as to keep the vm_struct APIs independent of
+ * the physical/mapped size.
+ */
+ for (area->nr_pages = 0; area->nr_pages < nr_small_pages;
+ area->nr_pages += 1U << page_order) {
+ struct page *page;
+ int i;
+
+ /* Compound pages required for remap_vmalloc_page */
+ page = alloc_pages_node(node, gfp_mask | __GFP_COMP, page_order);
+ if (unlikely(!page))
+ break;

- for (p = 0; p < (1U << page_order); p++)
- area->pages[i + p] = page + p;
+ for (i = 0; i < (1U << page_order); i++)
+ area->pages[area->nr_pages + i] = page + i;

- if (gfpflags_allow_blocking(gfp_mask))
- cond_resched();
+ if (gfpflags_allow_blocking(gfp_mask))
+ cond_resched();
+ }
}
+
atomic_long_add(area->nr_pages, &nr_vmalloc_pages);

- if (vmap_pages_range(addr, addr + size, prot, pages, page_shift) < 0) {
+ /*
+ * If not enough pages were obtained to accomplish an
+ * allocation request, free them via __vfree() if any.
+ */
+ if (area->nr_pages != nr_small_pages) {
+ warn_alloc(gfp_mask, NULL,
+ "vmalloc size %lu allocation failure: "
+ "page order %u allocation failed",
+ area->nr_pages * PAGE_SIZE, page_order);
+ goto fail;
+ }
+
+ if (vmap_pages_range(addr, addr + size, prot, area->pages, page_shift) < 0) {
warn_alloc(gfp_mask, NULL,
"vmalloc size %lu allocation failure: "
"failed to map pages",
--
2.20.1