On 06/21/2012 05:01 AM, Johannes Weiner wrote:
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index bf56d66..8ccb4e1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -307,6 +307,7 @@ struct mm_struct {
unsigned long task_size; /* size of task vm space */
unsigned long cached_hole_size; /* if non-zero, the largest hole below free_area_cache */
unsigned long free_area_cache; /* first hole of size cached_hole_size or larger */
+ unsigned long highest_vma; /* highest vma end address */
It's not clear from the name that this is an end address. Would
highest_vm_end be better?
Good idea. Will fix.
+ /* Find the left-most free area of sufficient size. */
+ for (addr = 0, rb_node = mm->mm_rb.rb_node; rb_node; ) {
+ unsigned long vma_start;
+ int found_here = 0;
+
+ vma = rb_to_vma(rb_node);
+
+ if (vma->vm_start> len) {
vmas can abut, and vma->vm_end == vma->vm_next->vm_start. Should this
be>=?
We do not want to mmap at address 0.
+ /* Go left if it looks promising. */
+ if (node_free_hole(rb_node->rb_left)>= len&&
+ vma->vm_start - len>= lower_limit) {
+ rb_node = rb_node->rb_left;
+ continue;
If we already are at a vma whose start has a lower address than the
overall length, does it make sense to check for a left hole?
I.e. shouldn't this be inside the if (vma->vm_start> len) block?
I am trying to preserve the same fragmentation
semantics as the current code, so we do not
get any regressions in that area.
+ /*
+ * There is not enough space to the left of any VMA.
+ * Check the far right-hand side of the VMA tree.
+ */
+ rb_node = mm->mm_rb.rb_node;
+ while (rb_node->rb_right)
+ rb_node = rb_node->rb_right;
+ vma = rb_to_vma(rb_node);
+ addr = vma->vm_end;
Unless I missed something, we only reach here when
continue_next_right(rb_node) above returned NULL. And if it does, the
rb_node it was passed was the right-most node in the tree, so we could
do something like
We break out of the large while() loop once rb_node
is NULL, due to falling off the end of the tree.
} else if (!addr) {
struct rb_node *rb_right = continue_next_right(rb_node);
if (!rb_right)
break;
rb_node = rb_right;
continue;
}
above and then save the lookup after the loop.
That might work, but I expect the situation to be rare
enough that I would rather pick the more readable option.
Also, dereferencing mm->mm_rb.rb_node unconditionally after the loop
assumes that the tree always contains at least one vma. Is this
guaranteed for all architectures?
When a process is execve'd, a stack VMA is set up.
This means every process has at least one VMA by the
time we can get to this code.
-fail:
- /*
- * if hint left us with no space for the requested
- * mapping then try again:
- *
- * Note: this is different with the case of bottomup
- * which does the fully line-search, but we use find_vma
- * here that causes some holes skipped.
- */
- if (start_addr != mm->mmap_base) {
- mm->free_area_cache = mm->mmap_base;
- mm->cached_hole_size = 0;
- goto try_again;
+ if (!found_here&& node_free_hole(rb_node->rb_left)>= len) {
+ /* Last known hole is to the right of this subtree. */
"to the left"
Thanks, will fix.
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