From: Wenchao Xia <wenchaolinux@xxxxxxxxx>
This option allow user space program getting a mirror for
mem, that is two virtual mapping. The content is COW so
it can be used for snapshot a region of mem.
Now shared memory is not COWED yet.
Signed-off-by: Wenchao Xia <wenchaolinux@xxxxxxxxx>
---
include/uapi/linux/mman.h | 1 +
mm/mremap.c | 103 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 102 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index ade4acd..5cf7816 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -5,6 +5,7 @@
#define MREMAP_MAYMOVE 1
#define MREMAP_FIXED 2
+#define MREMAP_DUP 4
#define OVERCOMMIT_GUESS 0
#define OVERCOMMIT_ALWAYS 1
diff --git a/mm/mremap.c b/mm/mremap.c
index 2cc1cae..f6cc29f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -391,6 +391,45 @@ static unsigned long move_vma(struct vm_area_struct *vma,
return new_addr;
}
+static unsigned long dup_vma(struct vm_area_struct *vma,
+ unsigned long old_addr, unsigned long new_addr,
+ unsigned long len, bool *locked)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct vm_area_struct *new_vma;
+ unsigned long vm_flags = vma->vm_flags;
+ unsigned long new_pgoff;
+ unsigned long duped_len;
+ int err;
+ bool need_rmap_locks;
+
+ new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
+ new_vma = copy_vma(&vma, new_addr, len, new_pgoff,
+ &need_rmap_locks);
+ if (!new_vma)
+ return -ENOMEM;
+
+ duped_len = move_page_tables(vma, old_addr, new_vma, new_addr, len,
+ need_rmap_locks, false);
+ if (duped_len < len) {
+ /* remove new duplicated area */
+ move_page_tables(new_vma, new_addr, vma, old_addr, duped_len,
+ true, true);
+ err = do_munmap(mm, new_addr, duped_len);
+ VM_BUG_ON(err < 0);
+ return -ENOMEM;
+ }
+
+ vm_stat_account(mm, vma->vm_flags, vma->vm_file, len>>PAGE_SHIFT);
+
+ if (vm_flags & VM_LOCKED) {
+ mm->locked_vm += len >> PAGE_SHIFT;
+ *locked = true;
+ }
+
+ return new_addr;
+}
+
static struct vm_area_struct *vma_to_resize(unsigned long addr,
unsigned long old_len, unsigned long new_len, unsigned long *p)
{
@@ -511,6 +550,59 @@ out:
return ret;
}
+static unsigned long mremap_dup(unsigned long old_addr, unsigned long new_addr,
+ unsigned long len, unsigned long flags,
+ bool *locked)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+ unsigned long ret = -EINVAL, map_flags = 0;
+
+ if (flags & MREMAP_FIXED) {
+ if (new_addr & ~PAGE_MASK)
+ goto out;
+ if (len > TASK_SIZE || new_addr > TASK_SIZE - len)
+ goto out;
+ /* Overlap */
+ if ((new_addr <= old_addr) && (new_addr + len) > old_addr)
+ goto out;
+ if ((old_addr <= new_addr) && (old_addr + len) > new_addr)
+ goto out;
+
+ map_flags = MAP_FIXED;
+ } else {
+ new_addr = 0;
+ }
+
+ vma = find_vma(mm, old_addr);
+
+ /* We can't remap across vm area boundaries */
+ if (!vma || vma->vm_start > old_addr || len > vma->vm_end - old_addr)
+ goto out;
+
+ /* Currently, shared mem can't be cowed */
+ if (vma->vm_flags & VM_MAYSHARE)
+ map_flags |= MAP_SHARED;
+
+ ret = get_unmapped_area(vma->vm_file, new_addr, len, vma->vm_pgoff +
+ ((old_addr - vma->vm_start) >> PAGE_SHIFT),
+ map_flags);
+ if (ret & ~PAGE_MASK)
+ goto out;
+
+ new_addr = ret;
+
+ /* for debug */
+ printk(KERN_WARNING
+ "mremap dup %lx with len %lx to %lx, original vm_flag %lx.",
+ old_addr, len, new_addr, vma->vm_flags);
+
+ ret = dup_vma(vma, old_addr, new_addr, len, locked);
+
+out:
+ return ret;
+}
+
static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
{
unsigned long end = vma->vm_end + delta;
@@ -543,7 +635,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
down_write(¤t->mm->mmap_sem);
- if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
+ if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DUP))
goto out;
if (addr & ~PAGE_MASK)
@@ -552,6 +644,10 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
old_len = PAGE_ALIGN(old_len);
new_len = PAGE_ALIGN(new_len);
+ if (flags & MREMAP_DUP) {
+ ret = mremap_dup(addr, new_addr, old_len, flags, &locked);
+ goto out;
+ }
/*
* We allow a zero old-len as a special case
* for DOS-emu "duplicate shm area" thing. But
@@ -638,7 +734,10 @@ out:
if (ret & ~PAGE_MASK)
vm_unacct_memory(charged);
up_write(¤t->mm->mmap_sem);
- if (locked && new_len > old_len)
+ /* locked == true only when operation success */
+ if ((flags & MREMAP_DUP) && (!IS_ERR_VALUE(ret)) && locked)
+ mm_populate(ret, old_len);
+ else if (locked && new_len > old_len)
mm_populate(new_addr + old_len, new_len - old_len);
return ret;
}
--
1.7.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>