Implement vm_unmapped_area() using the rb_subtree_gap and highest_vm_end
information to look up for suitable virtual address space gaps.
struct vm_unmapped_area_info is used to define the desired allocation
request:
- lowest or highest possible address matching the remaining constraints
- desired gap length
- low/high address limits that the gap must fit into
- alignment mask and offset
Also update the generic arch_get_unmapped_area[_topdown] functions to
make use of vm_unmapped_area() instead of implementing a brute force search.
Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
---
include/linux/mm.h | 31 +++++
mm/mmap.c | 312 +++++++++++++++++++++++++++++++++++++---------------
2 files changed, 253 insertions(+), 90 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index fa0680402738..441dfe8ea24d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1456,6 +1456,37 @@ extern unsigned long vm_mmap(struct file *, unsigned long,
unsigned long, unsigned long,
unsigned long, unsigned long);
+struct vm_unmapped_area_info {
+#define VM_UNMAPPED_AREA_TOPDOWN 1
+ unsigned long flags;
+ unsigned long length;
+ unsigned long low_limit;
+ unsigned long high_limit;
+ unsigned long align_mask;
+ unsigned long align_offset;
+};
+
+extern unsigned long unmapped_area(struct vm_unmapped_area_info *info);
+extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);
+
+/*
+ * Search for an unmapped address range.
+ *
+ * We are looking for a range that:
+ * - does not intersect with any VMA;
+ * - is contained within the [low_limit, high_limit) interval;
+ * - is at least the desired size.
+ * - satisfies (begin_addr & align_mask) == (align_offset & align_mask)
+ */
+static inline unsigned long
+vm_unmapped_area(struct vm_unmapped_area_info *info)
+{
+ if (!(info->flags & VM_UNMAPPED_AREA_TOPDOWN))
+ return unmapped_area(info);
+ else
+ return unmapped_area_topdown(info);
+}
+
/* truncate.c */
extern void truncate_inode_pages(struct address_space *, loff_t);
extern void truncate_inode_pages_range(struct address_space *,
diff --git a/mm/mmap.c b/mm/mmap.c
index 769a09cc71af..aa748988cd54 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1496,6 +1496,206 @@ unacct_error:
return error;
}
+unsigned long unmapped_area(struct vm_unmapped_area_info *info)
+{
+ /*
+ * We implement the search by looking for an rbtree node that
+ * immediately follows a suitable gap. That is,
+ * - gap_start = vma->vm_prev->vm_end <= info->high_limit - length;
+ * - gap_end = vma->vm_start >= info->low_limit + length;
+ * - gap_end - gap_start >= length
+ */
+
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+ unsigned long length, low_limit, high_limit, gap_start, gap_end;
+
+ /* Adjust search length to account for worst case alignment overhead */
+ length = info->length + info->align_mask;
+ if (length < info->length)
+ return -ENOMEM;
+
+ /* Adjust search limits by the desired length */
+ if (info->high_limit < length)
+ return -ENOMEM;
+ high_limit = info->high_limit - length;
+
+ if (info->low_limit > high_limit)
+ return -ENOMEM;
+ low_limit = info->low_limit + length;
+
+ /* Check if rbtree root looks promising */
+ if (RB_EMPTY_ROOT(&mm->mm_rb))
+ goto check_highest;
+ vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
+ if (vma->rb_subtree_gap < length)
+ goto check_highest;
+
+ while (true) {
+ /* Visit left subtree if it looks promising */
+ gap_end = vma->vm_start;
+ if (gap_end >= low_limit && vma->vm_rb.rb_left) {
+ struct vm_area_struct *left =
+ rb_entry(vma->vm_rb.rb_left,
+ struct vm_area_struct, vm_rb);
+ if (left->rb_subtree_gap >= length) {
+ vma = left;
+ continue;
+ }
+ }
+
+ gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
+ check_current:
+ /* Check if current node has a suitable gap */
+ if (gap_start > high_limit)
+ return -ENOMEM;
+ if (gap_end >= low_limit && gap_end - gap_start >= length)
+ goto found;
+
+ /* Visit right subtree if it looks promising */
+ if (vma->vm_rb.rb_right) {
+ struct vm_area_struct *right =
+ rb_entry(vma->vm_rb.rb_right,
+ struct vm_area_struct, vm_rb);
+ if (right->rb_subtree_gap >= length) {
+ vma = right;
+ continue;
+ }
+ }
+
+ /* Go back up the rbtree to find next candidate node */
+ while (true) {
+ struct rb_node *prev = &vma->vm_rb;
+ if (!rb_parent(prev))
+ goto check_highest;
+ vma = rb_entry(rb_parent(prev),
+ struct vm_area_struct, vm_rb);
+ if (prev == vma->vm_rb.rb_left) {
+ gap_start = vma->vm_prev->vm_end;
+ gap_end = vma->vm_start;
+ goto check_current;
+ }
+ }
+ }
+
+check_highest:
+ /* Check highest gap, which does not precede any rbtree node */
+ gap_start = mm->highest_vm_end;
+ gap_end = ULONG_MAX; /* Only for VM_BUG_ON below */
+ if (gap_start > high_limit)
+ return -ENOMEM;
+
+found:
+ /* We found a suitable gap. Clip it with the original low_limit. */
+ if (gap_start < info->low_limit)
+ gap_start = info->low_limit;
+
+ /* Adjust gap address to the desired alignment */
+ gap_start += (info->align_offset - gap_start) & info->align_mask;
+
+ VM_BUG_ON(gap_start + info->length > info->high_limit);
+ VM_BUG_ON(gap_start + info->length > gap_end);
+ return gap_start;
+}
+
+unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+ unsigned long length, low_limit, high_limit, gap_start, gap_end;
+
+ /* Adjust search length to account for worst case alignment overhead */
+ length = info->length + info->align_mask;
+ if (length < info->length)
+ return -ENOMEM;
+
+ /*
+ * Adjust search limits by the desired length.
+ * See implementation comment at top of unmapped_area().
+ */
+ gap_end = info->high_limit;
+ if (gap_end < length)
+ return -ENOMEM;
+ high_limit = gap_end - length;
+
+ if (info->low_limit > high_limit)
+ return -ENOMEM;
+ low_limit = info->low_limit + length;
+
+ /* Check highest gap, which does not precede any rbtree node */
+ gap_start = mm->highest_vm_end;
+ if (gap_start <= high_limit)
+ goto found_highest;
+
+ /* Check if rbtree root looks promising */
+ if (RB_EMPTY_ROOT(&mm->mm_rb))
+ return -ENOMEM;
+ vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
+ if (vma->rb_subtree_gap < length)
+ return -ENOMEM;
+
+ while (true) {
+ /* Visit right subtree if it looks promising */
+ gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
+ if (gap_start <= high_limit && vma->vm_rb.rb_right) {
+ struct vm_area_struct *right =
+ rb_entry(vma->vm_rb.rb_right,
+ struct vm_area_struct, vm_rb);
+ if (right->rb_subtree_gap >= length) {
+ vma = right;
+ continue;
+ }
+ }
+
+ check_current:
+ /* Check if current node has a suitable gap */
+ gap_end = vma->vm_start;
+ if (gap_end < low_limit)
+ return -ENOMEM;
+ if (gap_start <= high_limit && gap_end - gap_start >= length)
+ goto found;
+
+ /* Visit left subtree if it looks promising */
+ if (vma->vm_rb.rb_left) {
+ struct vm_area_struct *left =
+ rb_entry(vma->vm_rb.rb_left,
+ struct vm_area_struct, vm_rb);
+ if (left->rb_subtree_gap >= length) {
+ vma = left;
+ continue;
+ }
+ }
+
+ /* Go back up the rbtree to find next candidate node */
+ while (true) {
+ struct rb_node *prev = &vma->vm_rb;
+ if (!rb_parent(prev))
+ return -ENOMEM;
+ vma = rb_entry(rb_parent(prev),
+ struct vm_area_struct, vm_rb);
+ if (prev == vma->vm_rb.rb_right) {
+ gap_start = vma->vm_prev ?
+ vma->vm_prev->vm_end : 0;
+ goto check_current;
+ }
+ }
+ }
+
+found:
+ /* We found a suitable gap. Clip it with the original high_limit. */
+ if (gap_end > info->high_limit)
+ gap_end = info->high_limit;
+
+found_highest:
+ /* Compute highest gap address at the desired alignment */
+ gap_end -= info->length;
+ gap_end -= (gap_end - info->align_offset) & info->align_mask;
+
+ VM_BUG_ON(gap_end < info->low_limit);
+ VM_BUG_ON(gap_end < gap_start);
+ return gap_end;
+}
+
/* Get an address range which is currently unmapped.
* For shmat() with addr=0.
*
@@ -1514,7 +1714,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
- unsigned long start_addr;
+ struct vm_unmapped_area_info info;
if (len > TASK_SIZE)
return -ENOMEM;
@@ -1529,40 +1729,13 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
(!vma || addr + len <= vma->vm_start))
return addr;
}
- if (len > mm->cached_hole_size) {
- start_addr = addr = mm->free_area_cache;
- } else {
- start_addr = addr = TASK_UNMAPPED_BASE;
- mm->cached_hole_size = 0;
- }
-full_search:
- for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
- /* At this point: (!vma || addr < vma->vm_end). */
- if (TASK_SIZE - len < addr) {
- /*
- * Start a new search - just in case we missed
- * some holes.
- */
- if (start_addr != TASK_UNMAPPED_BASE) {
- addr = TASK_UNMAPPED_BASE;
- start_addr = addr;
- mm->cached_hole_size = 0;
- goto full_search;
- }
- return -ENOMEM;
- }
- if (!vma || addr + len <= vma->vm_start) {
- /*
- * Remember the place where we stopped the search:
- */
- mm->free_area_cache = addr + len;
- return addr;
- }
- if (addr + mm->cached_hole_size < vma->vm_start)
- mm->cached_hole_size = vma->vm_start - addr;
- addr = vma->vm_end;
- }
+ info.flags = 0;
+ info.length = len;
+ info.low_limit = TASK_UNMAPPED_BASE;
+ info.high_limit = TASK_SIZE;
+ info.align_mask = 0;
+ return vm_unmapped_area(&info);
}
#endif
@@ -1587,7 +1760,8 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
{
struct vm_area_struct *vma;
struct mm_struct *mm = current->mm;
- unsigned long addr = addr0, start_addr;
+ unsigned long addr = addr0;
+ struct vm_unmapped_area_info info;
/* requested length too big for entire address space */
if (len > TASK_SIZE)
@@ -1605,53 +1779,12 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
return addr;
}
- /* check if free_area_cache is useful for us */
- if (len <= mm->cached_hole_size) {
- mm->cached_hole_size = 0;
- mm->free_area_cache = mm->mmap_base;
- }
-
-try_again:
- /* either no address requested or can't fit in requested address hole */
- start_addr = addr = mm->free_area_cache;
-
- if (addr < len)
- goto fail;
-
- addr -= len;
- do {
- /*
- * Lookup failure means no vma is above this address,
- * else if new region fits below vma->vm_start,
- * return with success:
- */
- vma = find_vma(mm, addr);
- if (!vma || addr+len <= vma->vm_start)
- /* remember the address as a hint for next time */
- return (mm->free_area_cache = addr);
-
- /* remember the largest hole we saw so far */
- if (addr + mm->cached_hole_size < vma->vm_start)
- mm->cached_hole_size = vma->vm_start - addr;
-
- /* try just below the current vma->vm_start */
- addr = vma->vm_start-len;
- } while (len < vma->vm_start);
-
-fail:
- /*
- * if hint left us with no space for the requested
- * mapping then try again:
- *
- * Note: this is different with the case of bottomup
- * which does the fully line-search, but we use find_vma
- * here that causes some holes skipped.
- */
- if (start_addr != mm->mmap_base) {
- mm->free_area_cache = mm->mmap_base;
- mm->cached_hole_size = 0;
- goto try_again;
- }
+ info.flags = VM_UNMAPPED_AREA_TOPDOWN;
+ info.length = len;
+ info.low_limit = PAGE_SIZE;
+ info.high_limit = mm->mmap_base;
+ info.align_mask = 0;
+ addr = vm_unmapped_area(&info);
/*
* A failed mmap() very likely causes application failure,
@@ -1659,14 +1792,13 @@ fail:
* can happen with large stack limits and large mmap()
* allocations.
*/
- mm->cached_hole_size = ~0UL;
- mm->free_area_cache = TASK_UNMAPPED_BASE;
- addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
- /*
- * Restore the topdown base:
- */
- mm->free_area_cache = mm->mmap_base;
- mm->cached_hole_size = ~0UL;
+ if (addr & ~PAGE_MASK) {
+ VM_BUG_ON(addr != -ENOMEM);
+ info.flags = 0;
+ info.low_limit = TASK_UNMAPPED_BASE;
+ info.high_limit = TASK_SIZE;
+ addr = vm_unmapped_area(&info);
+ }
return addr;
}
--
1.7.7.3
