On 07/09, Oleg Nesterov wrote:
>
> I can be easily wrong, but to me vma_adjust() and its usage looks a bit
> overcomplicated. Perhaps it makes sense to distinguish mmapped/hole cases.
> mbind_range/madvise/etc need vma_join(vma, ...), not prev/anon_vma/file.
> Perhaps. not sure.
And I am just curious if something like below makes any sense...
Suppose we add the new helper, vma_update(vma, new). Note that "new" is
the fake vma, it just describes how do want to change vma.
static bool
can_merge_vma(struct vm_area_struct *prev, struct vm_area_struct *next)
{
if (prev->vm_end != next->vm_start)
return false;
if (prev->vm_pgoff + vma_pages(prev) != next->vm_pgoff)
return false;
if (prev->vm_file != next->vm_file)
return false;
if (prev->vm_flags != next->vm_flags)
return false;
if (!mpol_equal(vma_policy(prev), vma_policy(next)))
return false;
if (prev->anon_vma != next->anon_vma) /* WRONG, FIXME !!! */
return false;
if (next->vm_ops && next->vm_ops->close)
return false;
return true;
}
struct vm_area_struct *
vma_update(struct vm_area_struct *vma, struct vm_area_struct *new)
{
struct vm_area_struct *prev = vma->vm_prev;
struct vm_area_struct *next = vma->vm_next;
struct vm_area_struct *new_ret;
unsigned long new_end;
int err;
/* prev/next != vma means we can merge with prev/next */
if (!prev || !can_merge_vma(prev, new))
prev = vma;
if (!next || !can_merge_vma(new, next))
next = vma;
if (new->vm_start > vma->vm_start) { /* prev == vma */
if (next != vma) {
/* vma shrinks, next grows, case 4 */
new_end = new->vm_start;
new_ret = next;
goto adjust;
}
err = split_vma(vma->vm_mm, vma, new->vm_start, 1);
if (err)
return ERR_PTR(err);
}
if (new->vm_end < vma->vm_end) { /* next == vma */
if (prev != vma) {
/* prev grows, vma shrinks, case 5 */
new_end = new->vm_end;
new_ret = vma;
goto adjust;
}
err = split_vma(vma->vm_mm, vma, new->vm_end, 0);
if (err)
return ERR_PTR(err);
}
if (prev == next) /* true if split_vma() was called */
return vma;
new_end = next->vm_end;
new_ret = prev;
adjust:
err = vma_adjust(prev, prev->vm_start, new_end, prev->vm_pgoff, NULL);
if (err)
return ERR_PTR(err);
khugepaged_enter_vma_merge(new_ret);
return new_ret;
}
Now we can change madvise_behavior() and other similar users as below.
As for mmap_region() we can add another helper which simply tries to
expand prev/next (case 1-3).
Oleg.
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -46,10 +46,9 @@ 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;
unsigned long new_flags = vma->vm_flags;
+ struct vm_area_struct new;
+ int error = 0;
switch (behavior) {
case MADV_NORMAL:
@@ -100,34 +99,21 @@ static long madvise_behavior(struct vm_area_struct * vma,
goto out;
}
- 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;
+ new = *vma;
+ new.vm_flags = new_flags;
+ new.vm_start = start;
+ new.vm_end = end;
+ vma = vma_update(vma, &new);
- if (start != vma->vm_start) {
- error = split_vma(mm, vma, start, 1);
- if (error)
- goto out;
- }
-
- if (end != vma->vm_end) {
- error = split_vma(mm, vma, end, 0);
- if (error)
- goto out;
+ if (IS_ERR(vma)) {
+ error = PTR_ERR(vma);
+ goto out;
}
-
-success:
/*
* vm_flags is protected by the mmap_sem held in write mode.
*/
vma->vm_flags = new_flags;
-
+ *prev = vma;
out:
if (error == -ENOMEM)
error = -EAGAIN;
--
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