Messages in this thread Patch in this message | | | From | Wei Yang <> | Subject | [PATCH 1/2] mm/mmap.c: update *next* gap after itself | Date | Mon, 26 Aug 2019 15:31:05 +0800 |
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Since we link a vma to the leaf of a rb_tree, *next* must be a parent of vma if *next* is not NULL. This means if we update *next* gap first, it will be re-update again if vma's gap is bigger.
For example, we have a vma tree like this:
a [0x9000, 0x10000] / \ b c [0x8000, 0x9000] [0x10000, 0x11000]
The gap for each node is:
a's gap = 0x8000 b's gap = 0x8000 c's gap = 0x0
Now we want to insert d [0x6000, 0x7000], then the tree look like this:
a [0x9000, 0x10000] / \ b c [0x8000, 0x9000] [0x10000, 0x11000] / d [0x6000, 0x7000]
b is the *next* of d. If we update b's gap first, it would be 0x1000 and propagate to a. And then when update d's gap, which is 0x6000 and propagate through b to a again.
If we update d's gap first, the un-consistent gap 0x1000 will not be propagated.
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> --- mm/mmap.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c index aa66753b175e..672ad7dc6b3c 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -587,12 +587,6 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm, void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, struct rb_node **rb_link, struct rb_node *rb_parent) { - /* Update tracking information for the gap following the new vma. */ - if (vma->vm_next) - vma_gap_update(vma->vm_next); - else - mm->highest_vm_end = vm_end_gap(vma); - /* * vma->vm_prev wasn't known when we followed the rbtree to find the * correct insertion point for that vma. As a result, we could not @@ -605,6 +599,13 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, rb_link_node(&vma->vm_rb, rb_parent, rb_link); vma->rb_subtree_gap = 0; vma_gap_update(vma); + + /* Update tracking information for the gap following the new vma. */ + if (vma->vm_next) + vma_gap_update(vma->vm_next); + else + mm->highest_vm_end = vm_end_gap(vma); + vma_rb_insert(vma, &mm->mm_rb); } -- 2.17.1
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