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mm: vm_unmapped_area() lookup function
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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>
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Michel Lespinasse authored and Linus Torvalds committed Dec 12, 2012
1 parent e4c6bfd commit db4fbfb
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Showing 2 changed files with 253 additions and 90 deletions.
31 changes: 31 additions & 0 deletions include/linux/mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 *,
Expand Down
312 changes: 222 additions & 90 deletions mm/mmap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1539,6 +1539,206 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
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.
*
Expand All @@ -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;
Expand All @@ -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

Expand All @@ -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)
Expand All @@ -1648,68 +1822,26 @@ 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,
* so fall back to the bottom-up function here. This scenario
* 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;
}
Expand Down

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