[PATCH] madvise: merge the maps

This attempts to merge back the split maps.  This code is mostly copied
from Chrisw's mlock merging from post 2.6.11 trees.  The only difference is
in munmapped_error handling.  Also passed prev to willneed/dontneed,
eventhogh they do not handle it now, since I felt it will be cleaner,
instead of handling prev in madvise_vma in some cases and in subfunction in
some cases.

Signed-off-by: Prasanna Meda <pmeda@akamai.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 51 insertions, 29 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index 75b81ad1f98c..e3108054733c 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -8,17 +8,20 @@
 #include <linux/mman.h>
 #include <linux/pagemap.h>
 #include <linux/syscalls.h>
+#include <linux/mempolicy.h>
 #include <linux/hugetlb.h>
 
 /*
  * We can potentially split a vm area into separate
  * areas, each area with its own behavior.
  */
-static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
-                             unsigned long end, int behavior)
+static long madvise_behavior(struct vm_area_struct * vma,
+                     struct vm_area_struct **prev,
+                     unsigned long start, unsigned long end, int behavior)
 {
         struct mm_struct * mm = vma->vm_mm;
         int error = 0;
+        pgoff_t pgoff;
         int new_flags = vma->vm_flags & ~VM_READHINTMASK;
 
         switch (behavior) {
@@ -32,8 +35,20 @@ static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
                 break;
         }
 
-        if (new_flags == vma->vm_flags)
-                goto out;
+        if (new_flags == vma->vm_flags) {
+                *prev = vma;
+                goto success;
+        }
+
+        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
+        *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
+                                vma->vm_file, pgoff, vma_policy(vma));
+        if (*prev) {
+                vma = *prev;
+                goto success;
+        }
+
+        *prev = vma;
 
         if (start != vma->vm_start) {
                 error = split_vma(mm, vma, start, 1);
@@ -56,6 +71,7 @@ static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
 out:
         if (error == -ENOMEM)
                 error = -EAGAIN;
+success:
         return error;
 }
 
@@ -63,6 +79,7 @@ out:
  * Schedule all required I/O operations.  Do not wait for completion.
  */
 static long madvise_willneed(struct vm_area_struct * vma,
+                             struct vm_area_struct ** prev,
                              unsigned long start, unsigned long end)
 {
         struct file *file = vma->vm_file;
@@ -70,6 +87,7 @@ static long madvise_willneed(struct vm_area_struct * vma,
         if (!file)
                 return -EBADF;
 
+        *prev = vma;
         start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
         if (end > vma->vm_end)
                 end = vma->vm_end;
@@ -100,8 +118,10 @@ static long madvise_willneed(struct vm_area_struct * vma,
  * dirty pages is already available as msync(MS_INVALIDATE).
  */
 static long madvise_dontneed(struct vm_area_struct * vma,
+                             struct vm_area_struct ** prev,
                              unsigned long start, unsigned long end)
 {
+        *prev = vma;
         if ((vma->vm_flags & VM_LOCKED) || is_vm_hugetlb_page(vma))
                 return -EINVAL;
 
@@ -116,8 +136,8 @@ static long madvise_dontneed(struct vm_area_struct * vma,
         return 0;
 }
 
-static long madvise_vma(struct vm_area_struct * vma, unsigned long start,
-                        unsigned long end, int behavior)
+static long madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
+                        unsigned long start, unsigned long end, int behavior)
 {
         long error = -EBADF;
 
@@ -125,15 +145,15 @@ static long madvise_vma(struct vm_area_struct * vma, unsigned long start,
         case MADV_NORMAL:
         case MADV_SEQUENTIAL:
         case MADV_RANDOM:
-                error = madvise_behavior(vma, start, end, behavior);
+                error = madvise_behavior(vma, prev, start, end, behavior);
                 break;
 
         case MADV_WILLNEED:
-                error = madvise_willneed(vma, start, end);
+                error = madvise_willneed(vma, prev, start, end);
                 break;
 
         case MADV_DONTNEED:
-                error = madvise_dontneed(vma, start, end);
+                error = madvise_dontneed(vma, prev, start, end);
                 break;
 
         default:
@@ -180,8 +200,8 @@ static long madvise_vma(struct vm_area_struct * vma, unsigned long start,
  */
 asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
 {
-        unsigned long end;
-        struct vm_area_struct * vma;
+        unsigned long end, tmp;
+        struct vm_area_struct * vma, *prev;
         int unmapped_error = 0;
         int error = -EINVAL;
         size_t len;
@@ -207,40 +227,42 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
         /*
          * If the interval [start,end) covers some unmapped address
          * ranges, just ignore them, but return -ENOMEM at the end.
+         * - different from the way of handling in mlock etc.
          */
-        vma = find_vma(current->mm, start);
+        vma = find_vma_prev(current->mm, start, &prev);
+        if (!vma && prev)
+                vma = prev->vm_next;
         for (;;) {
                 /* Still start < end. */
                 error = -ENOMEM;
                 if (!vma)
                         goto out;
 
-                /* Here start < vma->vm_end. */
+                /* Here start < (end|vma->vm_end). */
                 if (start < vma->vm_start) {
                         unmapped_error = -ENOMEM;
                         start = vma->vm_start;
+                        if (start >= end)
+                                goto out;
                 }
 
-                /* Here vma->vm_start <= start < vma->vm_end. */
-                if (end <= vma->vm_end) {
-                        if (start < end) {
-                                error = madvise_vma(vma, start, end,
-                                                        behavior);
-                                if (error)
-                                        goto out;
-                        }
-                        error = unmapped_error;
-                        goto out;
-                }
+                /* Here vma->vm_start <= start < (end|vma->vm_end) */
+                tmp = vma->vm_end;
+                if (end < tmp)
+                        tmp = end;
 
-                /* Here vma->vm_start <= start < vma->vm_end < end. */
-                error = madvise_vma(vma, start, vma->vm_end, behavior);
+                /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
+                error = madvise_vma(vma, &prev, start, tmp, behavior);
                 if (error)
                         goto out;
-                start = vma->vm_end;
-                vma = vma->vm_next;
+                start = tmp;
+                if (start < prev->vm_end)
+                        start = prev->vm_end;
+                error = unmapped_error;
+                if (start >= end)
+                        goto out;
+                vma = prev->vm_next;
         }
-
 out:
         up_write(&current->mm->mmap_sem);
         return error;