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Subject[PATCH v2 3/4] resources: allocate space within a region from the top down
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Date

Allocate space from the top of a region first, then work downward.

When we allocate space from a resource, we look for gaps between children
of the resource. Previously, we looked at gaps from the bottom up. For
example, given this:

[mem 0xbff00000-0xf7ffffff] PCI Bus 0000:00
[mem 0xc0000000-0xdfffffff] PCI Bus 0000:02
we attempted to allocate from the [mem 0xbff00000-0xbfffffff] gap first,
then the [mem 0xe0000000-0xf7ffffff] gap.
With this patch, we allocate from [mem 0xe0000000-0xf7ffffff] first.
Low addresses are generally scarce, so it's better to use high addresses
when possible. This follows Windows practice for PCI allocation.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=16228#c42
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
---
kernel/resource.c | 40 ++++++++++++++++++++++++----------------
1 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index ace2269..1a2a40e 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -358,6 +358,20 @@ int __weak page_is_ram(unsigned long pfn)
}

/*
+ * Find the resource before "child" in the sibling list of "root" children.
+ */
+static struct resource *find_sibling_prev(struct resource *root, struct resource *child)
+{
+ struct resource *this;
+
+ for (this = root->child; this; this = this->sibling)
+ if (this->sibling == child)
+ return this;
+
+ return NULL;
+}
+
+/*
* Find empty slot in the resource tree given range and alignment.
*/
static int find_resource(struct resource *root, struct resource *new,
@@ -369,24 +383,18 @@ static int find_resource(struct resource *root, struct resource *new,
resource_size_t),
void *alignf_data)
{
- struct resource *this = root->child;
+ struct resource *this;
struct resource tmp = *new;
resource_size_t start;

- tmp.start = root->start;
- /*
- * Skip past an allocated resource that starts at 0, since the assignment
- * of this->start - 1 to tmp->end below would cause an underflow.
- */
- if (this && this->start == 0) {
- tmp.start = this->end + 1;
- this = this->sibling;
- }
- for(;;) {
+ tmp.end = root->end;
+
+ this = find_sibling_prev(root, NULL);
+ for (;;) {
if (this)
- tmp.end = this->start - 1;
+ tmp.start = this->end + 1;
else
- tmp.end = root->end;
+ tmp.start = root->start;
if (tmp.start < min)
tmp.start = min;
if (tmp.end > max)
@@ -404,10 +412,10 @@ static int find_resource(struct resource *root, struct resource *new,
new->end = tmp.start + size - 1;
return 0;
}
- if (!this)
+ if (!this || this->start == root->start)
break;
- tmp.start = this->end + 1;
- this = this->sibling;
+ tmp.end = this->start - 1;
+ this = find_sibling_prev(root, this);
}
return -EBUSY;
}


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