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Subject[PATCH v5 5/9] resources: support allocating space within a region from the top down
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Allocate space from the top of a region first, then work downward,
if an architecture desires this.

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

[mem 0xbff00000-0xf7ffffff] PCI Bus 0000:00
[mem 0xbff00000-0xbfffffff] gap -- available
[mem 0xc0000000-0xdfffffff] PCI Bus 0000:02
[mem 0xe0000000-0xf7ffffff] gap -- available
we attempted to allocate from the [mem 0xbff00000-0xbfffffff] gap first,
then the [mem 0xe0000000-0xf7ffffff] gap.
With this patch an architecture can choose to allocate from the top gap
[mem 0xe0000000-0xf7ffffff] first.
We can't do this across the board because iomem_resource.end is initialized
to 0xffffffff_ffffffff on 64-bit architectures, and most machines can't
address the entire 64-bit physical address space. Therefore, we only
allocate top-down if the arch requests it by clearing
"resource_alloc_from_bottom".
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
---
Documentation/kernel-parameters.txt | 5 ++
include/linux/ioport.h | 1
kernel/resource.c | 98 ++++++++++++++++++++++++++++++++++-
3 files changed, 100 insertions(+), 4 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4bc2f3c..ed45e98 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2175,6 +2175,11 @@ and is between 256 and 4096 characters. It is defined in the file
reset_devices [KNL] Force drivers to reset the underlying device
during initialization.

+ resource_alloc_from_bottom
+ Allocate new resources from the beginning of available
+ space, not the end. If you need to use this, please
+ report a bug.
+
resume= [SWSUSP]
Specify the partition device for software suspend

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index b227902..d377ea8 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -112,6 +112,7 @@ struct resource_list {
/* PC/ISA/whatever - the normal PC address spaces: IO and memory */
extern struct resource ioport_resource;
extern struct resource iomem_resource;
+extern int resource_alloc_from_bottom;

extern struct resource *request_resource_conflict(struct resource *root, struct resource *new);
extern int request_resource(struct resource *root, struct resource *new);
diff --git a/kernel/resource.c b/kernel/resource.c
index e15b922..716b680 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -40,6 +40,23 @@ EXPORT_SYMBOL(iomem_resource);

static DEFINE_RWLOCK(resource_lock);

+/*
+ * By default, we allocate free space bottom-up. The architecture can request
+ * top-down by clearing this flag. The user can override the architecture's
+ * choice with the "resource_alloc_from_bottom" kernel boot option, but that
+ * should only be a debugging tool.
+ */
+int resource_alloc_from_bottom = 1;
+
+static __init int setup_alloc_from_bottom(char *s)
+{
+ printk(KERN_INFO
+ "resource: allocating from bottom-up; please report a bug\n");
+ resource_alloc_from_bottom = 1;
+ return 0;
+}
+early_param("resource_alloc_from_bottom", setup_alloc_from_bottom);
+
static void *r_next(struct seq_file *m, void *v, loff_t *pos)
{
struct resource *p = v;
@@ -380,7 +397,74 @@ static bool resource_contains(struct resource *res1, struct resource *res2)
}

/*
+ * 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.
+ * This version allocates from the end of the root resource first.
+ */
+static int find_resource_from_top(struct resource *root, struct resource *new,
+ resource_size_t size, resource_size_t min,
+ resource_size_t max, resource_size_t align,
+ resource_size_t (*alignf)(void *,
+ const struct resource *,
+ resource_size_t,
+ resource_size_t),
+ void *alignf_data)
+{
+ struct resource *this;
+ struct resource tmp, avail, alloc;
+
+ tmp.start = root->end;
+ tmp.end = root->end;
+
+ this = find_sibling_prev(root, NULL);
+ for (;;) {
+ if (this) {
+ if (this->end < root->end)
+ tmp.start = this->end + 1;
+ } else
+ tmp.start = root->start;
+
+ resource_clip(&tmp, min, max);
+
+ /* Check for overflow after ALIGN() */
+ avail = *new;
+ avail.start = ALIGN(tmp.start, align);
+ avail.end = tmp.end;
+ if (avail.start >= tmp.start) {
+ alloc.start = alignf(alignf_data, &avail, size, align);
+ alloc.end = alloc.start + size - 1;
+ if (resource_contains(&avail, &alloc)) {
+ new->start = alloc.start;
+ new->end = alloc.end;
+ return 0;
+ }
+ }
+
+ if (!this || this->start == root->start)
+ break;
+
+ tmp.end = this->start - 1;
+ this = find_sibling_prev(root, this);
+ }
+ return -EBUSY;
+}
+
+/*
* Find empty slot in the resource tree given range and alignment.
+ * This version allocates from the beginning of the root resource first.
*/
static int find_resource(struct resource *root, struct resource *new,
resource_size_t size, resource_size_t min,
@@ -396,14 +480,15 @@ static int find_resource(struct resource *root, struct resource *new,

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.
+ * 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(;;) {
+ for (;;) {
if (this)
tmp.end = this->start - 1;
else
@@ -424,8 +509,10 @@ static int find_resource(struct resource *root, struct resource *new,
return 0;
}
}
+
if (!this)
break;
+
tmp.start = this->end + 1;
this = this->sibling;
}
@@ -458,7 +545,10 @@ int allocate_resource(struct resource *root, struct resource *new,
alignf = simple_align_resource;

write_lock(&resource_lock);
- err = find_resource(root, new, size, min, max, align, alignf, alignf_data);
+ if (resource_alloc_from_bottom)
+ err = find_resource(root, new, size, min, max, align, alignf, alignf_data);
+ else
+ err = find_resource_from_top(root, new, size, min, max, align, alignf, alignf_data);
if (err >= 0 && __request_resource(root, new))
err = -EBUSY;
write_unlock(&resource_lock);


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