Add new MAP_CONTIG flag to mmap system call. Check for flag in normal
mmap flag processing. If present, pre-allocate a contiguous set of
pages to back the mapping. These pages will be used a fault time, and
the MAP_CONTIG flag implies populating the mapping at the mmap time.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
include/uapi/asm-generic/mman.h | 1 +
mm/mmap.c | 94 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 95 insertions(+)
diff --git a/include/uapi/asm-generic/mman.h b/include/uapi/asm-generic/mman.h
index 7162cd4cca73..e8046b4c4ac4 100644
--- a/include/uapi/asm-generic/mman.h
+++ b/include/uapi/asm-generic/mman.h
@@ -12,6 +12,7 @@
#define MAP_NONBLOCK 0x10000 /* do not block on IO */
#define MAP_STACK 0x20000 /* give out an address that is best suited for process/thread stacks */
#define MAP_HUGETLB 0x40000 /* create a huge page mapping */
+#define MAP_CONTIG 0x80000 /* back with contiguous pages */
/* Bits [26:31] are reserved, see mman-common.h for MAP_HUGETLB usage */
diff --git a/mm/mmap.c b/mm/mmap.c
index 680506faceae..aee7917ee073 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -167,6 +167,16 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
{
struct vm_area_struct *next = vma->vm_next;
+ if (vma->vm_flags & VM_CONTIG) {
+ /*
+ * Do any necessary clean up when freeing a vma backed
+ * by a contiguous allocation.
+ *
+ * Not very useful in it's present form.
+ */
+ VM_BUG_ON(!vma->vm_private_data);
+ vma->vm_private_data = NULL;
+ }
might_sleep();
if (vma->vm_ops && vma->vm_ops->close)
vma->vm_ops->close(vma);
@@ -1378,6 +1388,18 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+ /*
+ * MAP_CONTIG has some restrictions,
+ * and also implies additional mmap and vma flags.
+ */
+ if (flags & MAP_CONTIG) {
+ if (!(flags & MAP_ANONYMOUS))
+ return -EINVAL;
+
+ flags |= MAP_POPULATE | MAP_LOCKED;
+ vm_flags |= (VM_CONTIG | VM_LOCKED | VM_DONTEXPAND);
+ }
+
if (flags & MAP_LOCKED)
if (!can_do_mlock())
return -EPERM;
@@ -1547,6 +1569,71 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
#endif /* __ARCH_WANT_SYS_OLD_MMAP */
/*
+ * Attempt to allocate a contiguous range of pages to back the
+ * specified vma. vm_private_data is used as a 'pointer' to the
+ * allocated pages. Larger requests and more fragmented memory
+ * make the allocation more likely to fail. So, caller must deal
+ * with this situation.
+ */
+static long __alloc_vma_contig_range(struct vm_area_struct *vma)
+{
+ gfp_t gfp = GFP_HIGHUSER | __GFP_ZERO;
+ unsigned long order;
+
+ VM_BUG_ON_VMA(vma->vm_private_data != NULL, vma);
+ order = get_order(vma->vm_end - vma->vm_start);
+
+ /*
+ * FIXME - Incomplete implementation. For now, just handle
+ * allocations < MAX_ORDER in size. However, this should really
+ * handle arbitrary size allocations.
+ */
+ if (order >= MAX_ORDER)
+ return -ENOMEM;
+
+ vma->vm_private_data = alloc_pages_vma(gfp, order, vma, vma->vm_start,
+ numa_node_id(), false);
+ if (!vma->vm_private_data)
+ return -ENOMEM;
+
+ /*
+ * split large allocation so it can be treated as individual
+ * pages when populating the mapping and at unmap time.
+ */
+ if (order) {
+ unsigned long vma_pages = (vma->vm_end - vma->vm_start) /
+ PAGE_SIZE;
+ unsigned long order_pages = 1 << order;
+ unsigned long i;
+ struct page *page = vma->vm_private_data;
+
+ split_page((struct page *)vma->vm_private_data, order);
+
+ /*
+ * 'order' rounds up size of vma to next power of 2. We
+ * will not need/use the extra pages so free them now.
+ */
+ for (i = vma_pages; i < order_pages; i++)
+ put_page(page + i);
+ }
+
+ return 0;
+}
+
+static void __free_vma_contig_range(struct vm_area_struct *vma)
+{
+ struct page *page = vma->vm_private_data;
+ unsigned long n_pages = (vma->vm_end - vma->vm_start) / PAGE_SIZE;
+ unsigned long i;
+
+ if (!page)
+ return;
+
+ for (i = 0; i < n_pages; i++)
+ put_page(page + i);
+}
+
+/*
* Some shared mappigns will want the pages marked read-only
* to track write events. If so, we'll downgrade vm_page_prot
* to the private version (using protection_map[] without the
@@ -1669,6 +1756,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vma->vm_pgoff = pgoff;
INIT_LIST_HEAD(&vma->anon_vma_chain);
+ if (vm_flags & VM_CONTIG) {
+ error = __alloc_vma_contig_range(vma);
+ if (error)
+ goto free_vma;
+ }
+
if (file) {
if (vm_flags & VM_DENYWRITE) {
error = deny_write_access(file);
@@ -1758,6 +1851,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
free_vma:
+ __free_vma_contig_range(vma);
kmem_cache_free(vm_area_cachep, vma);
unacct_error:
if (charged)
--
2.13.6
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