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Subject[PATCH v3 8/8] mm/vmalloc: Hugepage vmalloc mappings
Date
On platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmaps,
vmalloc will attempt to allocate PMD-sized pages first, before falling
back to small pages.

Allocations which use something other than PAGE_KERNEL protections are
not permitted to use huge pages yet, not all callers expect this (e.g.,
module allocations vs strict module rwx).

This reduces TLB misses by nearly 30x on a `git diff` workload on a
2-node POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%.

This can result in more internal fragmentation and memory overhead for a
given allocation, an option nohugevmap is added to disable at boot.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
.../admin-guide/kernel-parameters.txt | 2 +
include/linux/vmalloc.h | 1 +
mm/vmalloc.c | 174 +++++++++++++-----
3 files changed, 135 insertions(+), 42 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 98ea67f27809..eaef176c597f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3190,6 +3190,8 @@

nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.

+ nohugevmap [KNL,x86,PPC] Disable kernel huge vmalloc mappings.
+
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index e3590e93bfff..8f25dbaca0a1 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -58,6 +58,7 @@ struct vm_struct {
unsigned long size;
unsigned long flags;
struct page **pages;
+ unsigned int page_order;
unsigned int nr_pages;
phys_addr_t phys_addr;
const void *caller;
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4e5cb7c7f780..a7728c7086bc 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -45,6 +45,19 @@
#include "internal.h"
#include "pgalloc-track.h"

+#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
+static bool __ro_after_init vmap_allow_huge = true;
+
+static int __init set_nohugevmap(char *str)
+{
+ vmap_allow_huge = false;
+ return 0;
+}
+early_param("nohugevmap", set_nohugevmap);
+#else /* CONFIG_HAVE_ARCH_HUGE_VMAP */
+static const bool vmap_allow_huge = false;
+#endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
bool is_vmalloc_addr(const void *x)
{
unsigned long addr = (unsigned long)x;
@@ -468,31 +481,12 @@ static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long en
return 0;
}

-/**
- * map_kernel_range_noflush - map kernel VM area with the specified pages
- * @addr: start of the VM area to map
- * @size: size of the VM area to map
- * @prot: page protection flags to use
- * @pages: pages to map
- *
- * Map PFN_UP(@size) pages at @addr. The VM area @addr and @size specify should
- * have been allocated using get_vm_area() and its friends.
- *
- * NOTE:
- * This function does NOT do any cache flushing. The caller is responsible for
- * calling flush_cache_vmap() on to-be-mapped areas before calling this
- * function.
- *
- * RETURNS:
- * 0 on success, -errno on failure.
- */
-int map_kernel_range_noflush(unsigned long addr, unsigned long size,
- pgprot_t prot, struct page **pages)
+static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,
+ pgprot_t prot, struct page **pages)
{
unsigned long start = addr;
- unsigned long end = addr + size;
- unsigned long next;
pgd_t *pgd;
+ unsigned long next;
int err = 0;
int nr = 0;
pgtbl_mod_mask mask = 0;
@@ -514,6 +508,65 @@ int map_kernel_range_noflush(unsigned long addr, unsigned long size,
return 0;
}

+static int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
+ pgprot_t prot, struct page **pages, unsigned int page_shift)
+{
+ WARN_ON(page_shift < PAGE_SHIFT);
+
+ if (page_shift == PAGE_SHIFT) {
+ return vmap_small_pages_range_noflush(addr, end, prot, pages);
+ } else {
+ unsigned int i, nr = (end - addr) >> page_shift;
+
+ for (i = 0; i < nr; i++) {
+ int err;
+
+ err = vmap_range_noflush(addr, addr + (1UL << page_shift),
+ __pa(page_address(pages[i])), prot, page_shift);
+ if (err)
+ return err;
+
+ addr += 1UL << page_shift;
+ }
+
+ return 0;
+ }
+}
+
+static int vmap_pages_range(unsigned long addr, unsigned long end,
+ pgprot_t prot, struct page **pages, unsigned int page_shift)
+{
+ int err;
+
+ err = vmap_pages_range_noflush(addr, end, prot, pages, page_shift);
+ flush_cache_vmap(addr, end);
+ return err;
+}
+
+/**
+ * map_kernel_range_noflush - map kernel VM area with the specified pages
+ * @addr: start of the VM area to map
+ * @size: size of the VM area to map
+ * @prot: page protection flags to use
+ * @pages: pages to map
+ *
+ * Map PFN_UP(@size) pages at @addr. The VM area @addr and @size specify should
+ * have been allocated using get_vm_area() and its friends.
+ *
+ * NOTE:
+ * This function does NOT do any cache flushing. The caller is responsible for
+ * calling flush_cache_vmap() on to-be-mapped areas before calling this
+ * function.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+int map_kernel_range_noflush(unsigned long addr, unsigned long size,
+ pgprot_t prot, struct page **pages)
+{
+ return vmap_pages_range_noflush(addr, addr + size, prot, pages, PAGE_SHIFT);
+}
+
int map_kernel_range(unsigned long start, unsigned long size, pgprot_t prot,
struct page **pages)
{
@@ -2274,9 +2327,11 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
if (unlikely(!size))
return NULL;

- if (flags & VM_IOREMAP)
- align = 1ul << clamp_t(int, get_count_order_long(size),
- PAGE_SHIFT, IOREMAP_MAX_ORDER);
+ if (flags & VM_IOREMAP) {
+ align = max(align,
+ 1ul << clamp_t(int, get_count_order_long(size),
+ PAGE_SHIFT, IOREMAP_MAX_ORDER));
+ }

area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
if (unlikely(!area))
@@ -2475,7 +2530,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
struct page *page = area->pages[i];

BUG_ON(!page);
- __free_pages(page, 0);
+ __free_pages(page, area->page_order);
+ i += 1 << area->page_order;
}
atomic_long_sub(area->nr_pages, &nr_vmalloc_pages);

@@ -2614,9 +2670,12 @@ void *vmap(struct page **pages, unsigned int count,
EXPORT_SYMBOL(vmap);

static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
- pgprot_t prot, int node)
+ pgprot_t prot, unsigned int page_shift, int node)
{
struct page **pages;
+ unsigned long addr = (unsigned long)area->addr;
+ unsigned long size = get_vm_area_size(area);
+ unsigned int page_order = page_shift - PAGE_SHIFT;
unsigned int nr_pages, array_size, i;
const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
@@ -2624,7 +2683,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
0 :
__GFP_HIGHMEM;

- nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
+ nr_pages = size >> PAGE_SHIFT;
array_size = (nr_pages * sizeof(struct page *));

/* Please note that the recursion is strictly bounded. */
@@ -2643,29 +2702,29 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,

area->pages = pages;
area->nr_pages = nr_pages;
+ area->page_order = page_order;

- for (i = 0; i < area->nr_pages; i++) {
+ for (i = 0; i < area->nr_pages; i += 1 << page_order) {
struct page *page;
+ int p;

- if (node == NUMA_NO_NODE)
- page = alloc_page(alloc_mask|highmem_mask);
- else
- page = alloc_pages_node(node, alloc_mask|highmem_mask, 0);
-
+ page = alloc_pages_node(node, alloc_mask|highmem_mask, page_order);
if (unlikely(!page)) {
/* Successfully allocated i pages, free them in __vunmap() */
area->nr_pages = i;
atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
goto fail;
}
- area->pages[i] = page;
+
+ for (p = 0; p < (1 << page_order); p++)
+ area->pages[i + p] = page + p;
+
if (gfpflags_allow_blocking(gfp_mask))
cond_resched();
}
atomic_long_add(area->nr_pages, &nr_vmalloc_pages);

- if (map_kernel_range((unsigned long)area->addr, get_vm_area_size(area),
- prot, pages) < 0)
+ if (vmap_pages_range(addr, addr + size, prot, pages, page_shift) < 0)
goto fail;

return area->addr;
@@ -2701,22 +2760,45 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
pgprot_t prot, unsigned long vm_flags, int node,
const void *caller)
{
- struct vm_struct *area;
+ struct vm_struct *area = NULL;
void *addr;
unsigned long real_size = size;
+ unsigned long real_align = align;
+ unsigned int shift = PAGE_SHIFT;

size = PAGE_ALIGN(size);
if (!size || (size >> PAGE_SHIFT) > totalram_pages())
goto fail;

- area = __get_vm_area_node(real_size, align, VM_ALLOC | VM_UNINITIALIZED |
+ if (vmap_allow_huge && (pgprot_val(prot) == pgprot_val(PAGE_KERNEL))) {
+ unsigned long size_per_node;
+
+ /*
+ * Try huge pages. Only try for PAGE_KERNEL allocations,
+ * others like modules don't yet expect huge pages in
+ * their allocations due to apply_to_page_range not
+ * supporting them.
+ */
+
+ size_per_node = size;
+ if (node == NUMA_NO_NODE)
+ size_per_node /= num_online_nodes();
+ if (size_per_node >= PMD_SIZE)
+ shift = PMD_SHIFT;
+ }
+
+again:
+ align = max(real_align, 1UL << shift);
+ size = ALIGN(real_size, align);
+
+ area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
vm_flags, start, end, node, gfp_mask, caller);
if (!area)
goto fail;

- addr = __vmalloc_area_node(area, gfp_mask, prot, node);
+ addr = __vmalloc_area_node(area, gfp_mask, prot, shift, node);
if (!addr)
- return NULL;
+ goto fail;

/*
* In this function, newly allocated vm_struct has VM_UNINITIALIZED
@@ -2730,8 +2812,16 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
return addr;

fail:
- warn_alloc(gfp_mask, NULL,
+ if (shift > PAGE_SHIFT) {
+ shift = PAGE_SHIFT;
+ goto again;
+ }
+
+ if (!area) {
+ /* Warn for area allocation, page allocations already warn */
+ warn_alloc(gfp_mask, NULL,
"vmalloc: allocation failure: %lu bytes", real_size);
+ }
return NULL;
}

--
2.23.0
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