bootmem: clean up alloc_bootmem_core

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

bdata->last_pos has been dropped.

bdata->last_success has been renamed to hint_idx and it is now an index
relative to the node's range.  Since further block searching might start
at this index, it is now set to the end of a succeeded allocation rather
than its beginning.

bdata->last_offset has been renamed to last_end_off to be more clear that
it represents the ending address of the last allocation relative to the
node.

[y-goto@jp.fujitsu.com: fix new alloc_bootmem_core()]
Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 76 insertions, 136 deletions

diff --git a/mm/bootmem.c b/mm/bootmem.c
index 300d126ec533..94ea612deccf 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -242,8 +242,9 @@ static void __init free_bootmem_core(bootmem_data_t *bdata, unsigned long addr,
          * considered reserved.
          */
 
-        if (addr >= bdata->node_boot_start && addr < bdata->last_success)
-                bdata->last_success = addr;
+        if (addr >= bdata->node_boot_start &&
+                        PFN_DOWN(addr - bdata->node_boot_start) < bdata->hint_idx)
+                bdata->hint_idx = PFN_DOWN(addr - bdata->node_boot_start);
 
         /*
          * Round up to index to the range.
@@ -431,36 +432,16 @@ int __init reserve_bootmem(unsigned long addr, unsigned long size,
 }
 #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, sidx, midx, 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;
 
@@ -468,126 +449,85 @@ alloc_bootmem_core(struct bootmem_data *bdata, unsigned long size,
                 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)
+        goal >>= PAGE_SHIFT;
+        limit >>= PAGE_SHIFT;
+
+        if (limit && max > limit)
+                max = limit;
+        if (max <= min)
                 return NULL;
 
-        end_pfn = bdata->node_low_pfn;
-        limit = PFN_DOWN(limit);
-        if (limit && end_pfn > limit)
-                end_pfn = limit;
+        step = max(align >> PAGE_SHIFT, 1UL);
 
-        eidx = end_pfn - PFN_DOWN(node_boot_start);
+        if (goal && min < goal && goal < max)
+                start = ALIGN(goal, step);
+        else
+                start = ALIGN(min, step);
 
-        /*
-         * 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;
-        }
+        sidx = start - PFN_DOWN(bdata->node_boot_start);
+        midx = max - PFN_DOWN(bdata->node_boot_start);
 
-        preferred = PFN_DOWN(ALIGN(preferred, align));
-        areasize = (size + PAGE_SIZE-1) / PAGE_SIZE;
-        incr = align >> PAGE_SHIFT ? : 1;
+        if (bdata->hint_idx > sidx) {
+                /* Make sure we retry on failure */
+                goal = 1;
+                sidx = ALIGN(bdata->hint_idx, step);
+        }
 
-restart_scan:
-        for (i = preferred; i < eidx;) {
-                unsigned long j;
+        while (1) {
+                int merge;
+                void *region;
+                unsigned long eidx, i, start_off, end_off;
+find_block:
+                sidx = find_next_zero_bit(bdata->node_bootmem_map, midx, sidx);
+                sidx = ALIGN(sidx, step);
+                eidx = sidx + PFN_UP(size);
 
-                i = find_next_zero_bit(node_bootmem_map, eidx, i);
-                i = ALIGN(i, incr);
-                if (i >= eidx)
+                if (sidx >= midx || eidx > midx)
                         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;
-        }
-
-        if (preferred > 0) {
-                preferred = 0;
-                goto restart_scan;
-        }
-        return NULL;
 
-found:
-        bdata->last_success = PFN_PHYS(start) + node_boot_start;
-        BUG_ON(start >= eidx);
+                for (i = sidx; i < eidx; i++)
+                        if (test_bit(i, bdata->node_bootmem_map)) {
+                                sidx = ALIGN(i, step);
+                                if (sidx == i)
+                                        sidx += step;
+                                goto find_block;
+                        }
 
-        /*
-         * 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);
+                if (bdata->last_end_off &&
+                                PFN_DOWN(bdata->last_end_off) + 1 == sidx)
+                        start_off = ALIGN(bdata->last_end_off, align);
+                else
+                        start_off = PFN_PHYS(sidx);
+
+                merge = PFN_DOWN(start_off) < sidx;
+                end_off = start_off + size;
+
+                bdata->last_end_off = end_off;
+                bdata->hint_idx = PFN_UP(end_off);
+
+                /*
+                 * Reserve the area now:
+                 */
+                for (i = PFN_DOWN(start_off) + merge;
+                                i < PFN_UP(end_off); i++)
+                        if (test_and_set_bit(i, bdata->node_bootmem_map))
+                                BUG();
+
+                region = phys_to_virt(bdata->node_boot_start + start_off);
+                memset(region, 0, size);
+                return region;
         }
 
-        bdebug("nid=%td 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;
+                sidx = 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;
 }
 
 /**