[PATCH mm-unstable v2 01/16] mm: Introduce generic_mmap_hint()

[Kalesh Singh]

Consolidate the hint searches from both directions (topdown and
bottomup) into generic_mmap_hint().

No functional change is introduced.

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---

Changes in v2:
  - MAP_FIXED case is also handled in arch_mmap_hint() since this is just a
    special case of the hint addr being "enforced", per Yang Shi.
  - Consolidate error handling in arch_mmap_hint().

 include/linux/sched/mm.h |  4 +++
 mm/mmap.c                | 76 ++++++++++++++++++++++++----------------
 2 files changed, 50 insertions(+), 30 deletions(-)

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 928a626725e6..edeec19d1708 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -201,6 +201,10 @@ unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm,
 					   unsigned long flags,
 					   vm_flags_t vm_flags);
 
+unsigned long generic_mmap_hint(struct file *filp, unsigned long addr,
+				unsigned long len, unsigned long pgoff,
+				unsigned long flags);
+
 unsigned long
 generic_get_unmapped_area(struct file *filp, unsigned long addr,
 			  unsigned long len, unsigned long pgoff,
diff --git a/mm/mmap.c b/mm/mmap.c
index df9154b15ef9..382b4eac5406 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -620,6 +620,47 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
 	return addr;
 }
 
+/*
+ * Look up unmapped area at the requested hint addr
+ *
+ * NOTE: MAP_FIXED is also handled here since it's a special case of
+ * enforcing the hint address.
+ *
+ * Returns:
+ *    ERR_VALUE: If the requested mapping is not valid
+ *    0: If there isn't a sufficiently large hole at the hint addr.
+ *    addr: If sufficient VA space is available at the hint address;
+ *          or MAP_FIXED was specified.
+ */
+unsigned long generic_mmap_hint(struct file *filp, unsigned long addr,
+				unsigned long len, unsigned long pgoff,
+				unsigned long flags)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma, *prev;
+	const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
+
+	/* requested length too big for entire address space */
+	if (len > mmap_end - mmap_min_addr)
+		return -ENOMEM;
+
+	if (flags & MAP_FIXED)
+		return addr;
+
+	if (!addr)
+		return 0;
+
+	addr = PAGE_ALIGN(addr);
+	vma = find_vma_prev(mm, addr, &prev);
+	if (mmap_end - len >= addr && addr >= mmap_min_addr &&
+	    (!vma || addr + len <= vm_start_gap(vma)) &&
+	    (!prev || addr >= vm_end_gap(prev)))
+		return addr;
+
+	/* Fallback to VA space search */
+	return 0;
+}
+
 /* Get an address range which is currently unmapped.
  * For shmat() with addr=0.
  *
@@ -637,25 +678,13 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
 			  unsigned long flags, vm_flags_t vm_flags)
 {
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma, *prev;
 	struct vm_unmapped_area_info info = {};
 	const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
 
-	if (len > mmap_end - mmap_min_addr)
-		return -ENOMEM;
-
-	if (flags & MAP_FIXED)
+	addr = generic_mmap_hint(filp, addr, len, pgoff, flags);
+	if (addr)
 		return addr;
 
-	if (addr) {
-		addr = PAGE_ALIGN(addr);
-		vma = find_vma_prev(mm, addr, &prev);
-		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
-		    (!vma || addr + len <= vm_start_gap(vma)) &&
-		    (!prev || addr >= vm_end_gap(prev)))
-			return addr;
-	}
-
 	info.length = len;
 	info.low_limit = mm->mmap_base;
 	info.high_limit = mmap_end;
@@ -685,27 +714,14 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 				  unsigned long len, unsigned long pgoff,
 				  unsigned long flags, vm_flags_t vm_flags)
 {
-	struct vm_area_struct *vma, *prev;
 	struct mm_struct *mm = current->mm;
 	struct vm_unmapped_area_info info = {};
 	const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
 
-	/* requested length too big for entire address space */
-	if (len > mmap_end - mmap_min_addr)
-		return -ENOMEM;
-
-	if (flags & MAP_FIXED)
-		return addr;
-
 	/* requesting a specific address */
-	if (addr) {
-		addr = PAGE_ALIGN(addr);
-		vma = find_vma_prev(mm, addr, &prev);
-		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
-				(!vma || addr + len <= vm_start_gap(vma)) &&
-				(!prev || addr >= vm_end_gap(prev)))
-			return addr;
-	}
+	addr = generic_mmap_hint(filp, addr, len, pgoff, flags);
+	if (addr)
+		return addr;
 
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;
-- 
2.47.0.338.g60cca15819-goog