mm: vm_unmapped_area() lookup function

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.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 222 insertions, 90 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index ff93f6c8436c..5646677a96d5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1539,6 +1539,206 @@ 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.
  *
@@ -1557,7 +1757,7 @@ 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;
@@ -1572,40 +1772,13 @@ 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  
 
@@ -1630,7 +1803,8 @@ 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)
@@ -1648,53 +1822,12 @@ 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,
@@ -1702,14 +1835,13 @@ 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;
 }