[PATCH -mm 08/14] bootmem: clean up alloc_bootmem_core

Johannes Weiner
2008-05-30T19:42:28Z

[-- Attachment #1: bootmem-cleanup-alloc_bootmem_core.patch --]
[-- Type: text/plain, Size: 7626 bytes --]

alloc_bootmem_core has become quite nasty to read over time. This is
a clean rewrite that keeps the semantics.

Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
---

include/linux/bootmem.h | 1
mm/bootmem.c | 208 ++++++++++++++++--------------------------------
2 files changed, 72 insertions(+), 137 deletions(-)

--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -427,36 +427,16 @@ int __init reserve_bootmem(unsigned long
}
#endif /* !CONFIG_HAVE_ARCH_BOOTMEM_NODE */

-/*
- * We 'merge' subsequent allocations to save space. We might 'lose'
- * some fraction of a page if allocations cannot be satisfied due to
- * size constraints on boxes where there is physical RAM space
- * fragmentation - in these cases (mostly large memory boxes) this
- * is not a problem.
- *
- * On low memory boxes we get it right in 100% of the cases.
- *
- * alignment has to be a power of 2 value.
- *
- * NOTE: This function is _not_ reentrant.
- */
-static void * __init
-alloc_bootmem_core(struct bootmem_data *bdata, unsigned long size,
- unsigned long align, unsigned long goal, unsigned long limit)
+static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
+ unsigned long size, unsigned long align,
+ unsigned long goal, unsigned long limit)
{
- unsigned long areasize, preferred;
- unsigned long i, start = 0, incr, eidx, end_pfn;
- void *ret;
- unsigned long node_boot_start;
- void *node_bootmem_map;
-
- if (!size) {
- printk("alloc_bootmem_core(): zero-sized request\n");
- BUG();
- }
- BUG_ON(align & (align-1));
+ unsigned long min, max, start, step;
+
+ BUG_ON(!size);
+ BUG_ON(align & (align - 1));
+ BUG_ON(limit && goal + size > limit);

- /* on nodes without memory - bootmem_map is NULL */
if (!bdata->node_bootmem_map)
return NULL;

@@ -464,126 +444,82 @@ alloc_bootmem_core(struct bootmem_data *
bdata - bootmem_node_data, size, PAGE_ALIGN(size) >> PAGE_SHIFT,
align, goal, limit);

- /* bdata->node_boot_start is supposed to be (12+6)bits alignment on x86_64 ? */
- node_boot_start = bdata->node_boot_start;
- node_bootmem_map = bdata->node_bootmem_map;
- if (align) {
- node_boot_start = ALIGN(bdata->node_boot_start, align);
- if (node_boot_start > bdata->node_boot_start)
- node_bootmem_map = (unsigned long *)bdata->node_bootmem_map +
- PFN_DOWN(node_boot_start - bdata->node_boot_start)/BITS_PER_LONG;
- }
+ min = PFN_DOWN(bdata->node_boot_start);
+ max = bdata->node_low_pfn;

- if (limit && node_boot_start >= limit)
- return NULL;
+ goal >>= PAGE_SHIFT;
+ limit >>= PAGE_SHIFT;

- end_pfn = bdata->node_low_pfn;
- limit = PFN_DOWN(limit);
- if (limit && end_pfn > limit)
- end_pfn = limit;
+ if (limit && max > limit)
+ max = limit;
+ if (max <= min)
+ return NULL;

- eidx = end_pfn - PFN_DOWN(node_boot_start);
+ step = max(align >> PAGE_SHIFT, 1UL);

- /*
- * We try to allocate bootmem pages above 'goal'
- * first, then we try to allocate lower pages.
- */
- preferred = 0;
- if (goal && PFN_DOWN(goal) < end_pfn) {
- if (goal > node_boot_start)
- preferred = goal - node_boot_start;
-
- if (bdata->last_success > node_boot_start &&
- bdata->last_success - node_boot_start >= preferred)
- if (!limit || (limit && limit > bdata->last_success))
- preferred = bdata->last_success - node_boot_start;
+ if (goal && goal < max)
+ start = ALIGN(goal, step);
+ else
+ start = ALIGN(min, step);
+
+ if (bdata->last_success > start) {
+ /* Set goal here to trigger a retry on failure */
+ start = goal = ALIGN(bdata->last_success, step);
}

- preferred = PFN_DOWN(ALIGN(preferred, align));
- areasize = (size + PAGE_SIZE-1) / PAGE_SIZE;
- incr = align >> PAGE_SHIFT ? : 1;
-
-restart_scan:
- for (i = preferred; i < eidx;) {
- unsigned long j;
-
- i = find_next_zero_bit(node_bootmem_map, eidx, i);
- i = ALIGN(i, incr);
- if (i >= eidx)
- break;
- if (test_bit(i, node_bootmem_map)) {
- i += incr;
- continue;
- }
- for (j = i + 1; j < i + areasize; ++j) {
- if (j >= eidx)
- goto fail_block;
- if (test_bit(j, node_bootmem_map))
- goto fail_block;
- }
- start = i;
- goto found;
- fail_block:
- i = ALIGN(j, incr);
- if (i == j)
- i += incr;
- }
+ max -= PFN_DOWN(bdata->node_boot_start);
+ start -= PFN_DOWN(bdata->node_boot_start);

- if (preferred > 0) {
- preferred = 0;
- goto restart_scan;
- }
- return NULL;
+ while (1) {
+ int merge;
+ void *region;
+ unsigned long end, i, new_start, new_end;
+find_block:
+ start = find_next_zero_bit(bdata->node_bootmem_map, max, start);
+ start = ALIGN(start, step);
+ end = start + PFN_UP(size);

-found:
- bdata->last_success = PFN_PHYS(start) + node_boot_start;
- BUG_ON(start >= eidx);
+ if (start >= max || end > max)
+ break;

- /*
- * Is the next page of the previous allocation-end the start
- * of this allocation's buffer? If yes then we can 'merge'
- * the previous partial page with this allocation.
- */
- if (align < PAGE_SIZE &&
- bdata->last_offset && bdata->last_pos+1 == start) {
- unsigned long offset, remaining_size;
- offset = ALIGN(bdata->last_offset, align);
- BUG_ON(offset > PAGE_SIZE);
- remaining_size = PAGE_SIZE - offset;
- if (size < remaining_size) {
- areasize = 0;
- /* last_pos unchanged */
- bdata->last_offset = offset + size;
- ret = phys_to_virt(bdata->last_pos * PAGE_SIZE +
- offset + node_boot_start);
- } else {
- remaining_size = size - remaining_size;
- areasize = (remaining_size + PAGE_SIZE-1) / PAGE_SIZE;
- ret = phys_to_virt(bdata->last_pos * PAGE_SIZE +
- offset + node_boot_start);
- bdata->last_pos = start + areasize - 1;
- bdata->last_offset = remaining_size;
- }
- bdata->last_offset &= ~PAGE_MASK;
- } else {
- bdata->last_pos = start + areasize - 1;
- bdata->last_offset = size & ~PAGE_MASK;
- ret = phys_to_virt(start * PAGE_SIZE + node_boot_start);
+ for (i = start; i < end; i++)
+ if (test_bit(i, bdata->node_bootmem_map)) {
+ start = ALIGN(i, step);
+ if (start == i)
+ start += step;
+ goto find_block;
+ }
+
+ if (bdata->last_offset &&
+ PFN_DOWN(bdata->last_offset) + 1 == start)
+ new_start = ALIGN(bdata->last_offset, align);
+ else
+ new_start = PFN_PHYS(start);
+
+ merge = PFN_DOWN(new_start) < start;
+ new_end = new_start + size;
+
+ bdata->last_offset = new_end;
+
+ /*
+ * Reserve the area now:
+ */
+ for (i = PFN_DOWN(new_start) + merge; i < PFN_UP(new_end); i++)
+ if (test_and_set_bit(i, bdata->node_bootmem_map))
+ BUG();
+
+ region = phys_to_virt(bdata->node_boot_start + new_start);
+ memset(region, 0, size);
+ return region;
}

- bdebug("nid=%d start=%lx end=%lx\n",
- bdata - bootmem_node_data,
- start + PFN_DOWN(bdata->node_boot_start),
- start + areasize + PFN_DOWN(bdata->node_boot_start));
+ if (goal) {
+ goal = 0;
+ start = 0;
+ goto find_block;
+ }

- /*
- * Reserve the area now:
- */
- for (i = start; i < start + areasize; i++)
- if (unlikely(test_and_set_bit(i, node_bootmem_map)))
- BUG();
- memset(ret, 0, size);
- return ret;
+ return NULL;
}

/**
--- a/include/linux/bootmem.h
+++ b/include/linux/bootmem.h
@@ -32,7 +32,6 @@ typedef struct bootmem_data {
unsigned long node_low_pfn;
void *node_bootmem_map;
unsigned long last_offset;
- unsigned long last_pos;
unsigned long last_success; /* Previous allocation point. To speed
* up searching */
struct list_head list;