[RFC PATCH 03/15] mm/vmalloc: introduce new vrealloc() call and its subsidiary reach analog

[Roman Penyaev]

Function changes the size of virtual contigues memory, previously
allocated by vmalloc().

vrealloc() under the hood does the following:

 1. allocates new vm area based on the alignment of the old one.
 2. allocates pages array for a new vm area.
 3. fill in ->pages array taking pages from the old area increasing
    page ref.

    In case of virtual size grow (old_size < new_size) new pages
    for a new area are allocated using gfp passed by the caller.

Basically vrealloc() repeats glibc realloc() with only one big difference:
old area is not freed, i.e. caller is responsible for calling vfree() in
case of successfull reallocation.

Why vfree() is not called for old area directly from vrealloc()?  Because
sometimes it is better just to have transaction-like reallocation for
several pointers and reallocate all at once, i.e.:

  new_p1 = vrealloc(p1, new_len);
  new_p2 = vrealloc(p2, new_len);
  if (!new_p1 || !new_p2) {
	vfree(new_p1);
	vfree(new_p2);
	return -ENOMEM;
  }

  vfree(p1);
  vfree(p2);

  p1 = new_p1;
  p2 = new_p2;

Signed-off-by: Roman Penyaev <rpenyaev@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/vmalloc.h |   3 ++
 mm/vmalloc.c            | 106 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 78210aa0bb43..2902faf26c4f 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -72,6 +72,7 @@ static inline void vmalloc_init(void)
 
 extern void *vmalloc(unsigned long size);
 extern void *vzalloc(unsigned long size);
+extern void *vrealloc(void *old_addr, unsigned long size);
 extern void *vmalloc_user(unsigned long size);
 extern void *vmalloc_node(unsigned long size, int node);
 extern void *vzalloc_node(unsigned long size, int node);
@@ -83,6 +84,8 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			unsigned long start, unsigned long end, gfp_t gfp_mask,
 			pgprot_t prot, unsigned long vm_flags, int node,
 			const void *caller);
+extern void *__vrealloc_node(void *old_addr, unsigned long size, gfp_t gfp_mask,
+			     pgprot_t prot, int node, const void *caller);
 #ifndef CONFIG_MMU
 extern void *__vmalloc_node_flags(unsigned long size, int node, gfp_t flags);
 static inline void *__vmalloc_node_flags_caller(unsigned long size, int node,
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ad6cd807f6db..94cc99e780c7 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1889,6 +1889,112 @@ void *vzalloc(unsigned long size)
 }
 EXPORT_SYMBOL(vzalloc);
 
+void *__vrealloc_node(void *old_addr, unsigned long size, gfp_t gfp_mask,
+		      pgprot_t prot, int node, const void *caller)
+{
+	const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
+	const gfp_t highmem_mask = (gfp_mask & (GFP_DMA | GFP_DMA32)) ?	0 :
+					__GFP_HIGHMEM;
+	struct vm_struct *old_area, *area;
+	struct page *page;
+
+	unsigned int i;
+
+	old_area = find_vm_area(old_addr);
+	if (!old_area)
+		return NULL;
+
+	if (!(old_area->flags & VM_ALLOC))
+		return NULL;
+
+	size = PAGE_ALIGN(size);
+	if (!size || (size >> PAGE_SHIFT) > totalram_pages())
+		return NULL;
+
+	if (get_vm_area_size(old_area) == size)
+		return old_addr;
+
+	area = __get_vm_area_node(size, old_area->alignment, VM_UNINITIALIZED |
+				  old_area->flags, VMALLOC_START, VMALLOC_END,
+				  node, gfp_mask, caller);
+	if (!area)
+		return NULL;
+
+	if (alloc_vm_area_array(area, gfp_mask, node)) {
+		__vunmap(area->addr, 0);
+		return NULL;
+	}
+
+	for (i = 0; i < area->nr_pages; i++) {
+		if (i < old_area->nr_pages) {
+			/* Take a page from old area and increase a ref */
+
+			page = old_area->pages[i];
+			area->pages[i] = page;
+			get_page(page);
+		} else {
+			/* Allocate more pages in case of grow */
+
+			page = alloc_page(alloc_mask|highmem_mask);
+			if (unlikely(!page)) {
+				/*
+				 * Successfully allocated i pages, free
+				 * them in __vunmap()
+				 */
+				area->nr_pages = i;
+				goto fail;
+			}
+
+			area->pages[i] = page;
+			if (gfpflags_allow_blocking(gfp_mask|highmem_mask))
+				cond_resched();
+		}
+	}
+	if (map_vm_area(area, prot, area->pages))
+		goto fail;
+
+	/* New area is fully ready */
+	clear_vm_uninitialized_flag(area);
+	kmemleak_vmalloc(area, size, gfp_mask);
+
+	return area->addr;
+
+fail:
+	warn_alloc(gfp_mask, NULL, "vrealloc: allocation failure");
+	__vfree(area->addr);
+
+	return NULL;
+}
+EXPORT_SYMBOL(__vrealloc_node);
+
+/**
+ *	vrealloc - reallocate virtually contiguous memory with zero fill
+ *	@old_addr:	old virtual address
+ *	@size:		new size
+ *
+ *	Allocate additional pages to cover new @size from the page level
+ *	allocator if memory grows. Then pages are mapped into a new
+ *	contiguous kernel virtual space, previous area is NOT freed.
+ *
+ *	Do not forget to call vfree() passing old address.  But careful,
+ *	calling vfree() from interrupt will cause vfree_deferred() call,
+ *	which in its turn uses freed address as a temporal pointer for a
+ *	llist element, i.e. memory will be corrupted.
+ *
+ *	If new size is equal to the old size - old pointer is returned.
+ *	I.e. appropriate check should be made before calling vfree().
+ *
+ *	For tight control over page level allocator and protection flags
+ *	use __vrealloc_node() instead.
+ */
+void *vrealloc(void *old_addr, unsigned long size)
+{
+	return __vrealloc_node(old_addr, size, GFP_KERNEL | __GFP_ZERO,
+			       PAGE_KERNEL, NUMA_NO_NODE,
+			       __builtin_return_address(0));
+}
+EXPORT_SYMBOL(vrealloc);
+
 /**
  * vmalloc_user - allocate zeroed virtually contiguous memory for userspace
  * @size: allocation size
-- 
2.19.1