percpu: store offsets instead of lengths in ->map[]
Current code keeps +-length for each area in chunk->map[]. It has
several unpleasant consequences:
* even if we know that first 50 areas are all in use, allocation
still needs to go through all those areas just to sum their sizes, just
to get the offset of free one.
* freeing needs to find the array entry refering to the area
in question; again, the need to sum the sizes until we reach the offset
we are interested in. Note that offsets are monotonous, so simple
binary search would do here.
New data representation: array of <offset,in-use flag> pairs.
Each pair is represented by one int - we use offset|1 for <offset, in use>
and offset for <offset, free> (we make sure that all offsets are even).
In the end we put a sentry entry - <total size, in use>. The first
entry is <0, flag>; it would be possible to store together the flag
for Nth area and offset for N+1st, but that leads to much hairier code.
In other words, where the old variant would have
4, -8, -4, 4, -12, 100
(4 bytes free, 8 in use, 4 in use, 4 free, 12 in use, 100 free) we store
<0,0>, <4,1>, <12,1>, <16,0>, <20,1>, <32,0>, <132,1>
i.e.
0, 5, 13, 16, 21, 32, 133
This commit switches to new data representation and takes care of a couple
of low-hanging fruits in free_pcpu_area() - one is the switch to binary
search, another is not doing two memmove() when one would do. Speeding
the alloc side up (by keeping track of how many areas in the beginning are
known to be all in use) also becomes possible - that'll be done in the next
commit.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/percpu.c b/mm/percpu.c
index 592f289..49dfccf 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -102,7 +102,7 @@
int free_size; /* free bytes in the chunk */
int contig_hint; /* max contiguous size hint */
void *base_addr; /* base address of this chunk */
- int map_used; /* # of map entries used */
+ int map_used; /* # of map entries used before the sentry */
int map_alloc; /* # of map entries allocated */
int *map; /* allocation map */
void *data; /* chunk data */
@@ -356,11 +356,11 @@
{
int new_alloc;
- if (chunk->map_alloc >= chunk->map_used + 2)
+ if (chunk->map_alloc >= chunk->map_used + 3)
return 0;
new_alloc = PCPU_DFL_MAP_ALLOC;
- while (new_alloc < chunk->map_used + 2)
+ while (new_alloc < chunk->map_used + 3)
new_alloc *= 2;
return new_alloc;
@@ -441,19 +441,22 @@
int oslot = pcpu_chunk_slot(chunk);
int max_contig = 0;
int i, off;
+ int *p;
- for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++])) {
- bool is_last = i + 1 == chunk->map_used;
+ for (i = 0, p = chunk->map; i < chunk->map_used; i++, p++) {
int head, tail;
+ int this_size;
+
+ off = *p;
+ if (off & 1)
+ continue;
/* extra for alignment requirement */
head = ALIGN(off, align) - off;
- BUG_ON(i == 0 && head != 0);
- if (chunk->map[i] < 0)
- continue;
- if (chunk->map[i] < head + size) {
- max_contig = max(chunk->map[i], max_contig);
+ this_size = (p[1] & ~1) - off;
+ if (this_size < head + size) {
+ max_contig = max(this_size, max_contig);
continue;
}
@@ -463,55 +466,50 @@
* than sizeof(int), which is very small but isn't too
* uncommon for percpu allocations.
*/
- if (head && (head < sizeof(int) || chunk->map[i - 1] > 0)) {
- if (chunk->map[i - 1] > 0)
- chunk->map[i - 1] += head;
- else {
- chunk->map[i - 1] -= head;
+ if (head && (head < sizeof(int) || !(p[-1] & 1))) {
+ if (p[-1] & 1)
chunk->free_size -= head;
- }
- chunk->map[i] -= head;
- off += head;
+ *p = off += head;
+ this_size -= head;
head = 0;
}
/* if tail is small, just keep it around */
- tail = chunk->map[i] - head - size;
- if (tail < sizeof(int))
+ tail = this_size - head - size;
+ if (tail < sizeof(int)) {
tail = 0;
+ size = this_size - head;
+ }
/* split if warranted */
if (head || tail) {
int nr_extra = !!head + !!tail;
/* insert new subblocks */
- memmove(&chunk->map[i + nr_extra], &chunk->map[i],
+ memmove(p + nr_extra + 1, p + 1,
sizeof(chunk->map[0]) * (chunk->map_used - i));
chunk->map_used += nr_extra;
if (head) {
- chunk->map[i + 1] = chunk->map[i] - head;
- chunk->map[i] = head;
- off += head;
- i++;
+ *++p = off += head;
+ ++i;
max_contig = max(head, max_contig);
}
if (tail) {
- chunk->map[i] -= tail;
- chunk->map[i + 1] = tail;
+ p[1] = off + size;
max_contig = max(tail, max_contig);
}
}
/* update hint and mark allocated */
- if (is_last)
+ if (i + 1 == chunk->map_used)
chunk->contig_hint = max_contig; /* fully scanned */
else
chunk->contig_hint = max(chunk->contig_hint,
max_contig);
- chunk->free_size -= chunk->map[i];
- chunk->map[i] = -chunk->map[i];
+ chunk->free_size -= size;
+ *p |= 1;
pcpu_chunk_relocate(chunk, oslot);
return off;
@@ -539,34 +537,47 @@
static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme)
{
int oslot = pcpu_chunk_slot(chunk);
- int i, off;
+ int off = 0;
+ unsigned i, j;
+ int to_free = 0;
+ int *p;
- for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++]))
- if (off == freeme)
- break;
+ freeme |= 1; /* we are searching for <given offset, in use> pair */
+
+ i = 0;
+ j = chunk->map_used;
+ while (i != j) {
+ unsigned k = (i + j) / 2;
+ off = chunk->map[k];
+ if (off < freeme)
+ i = k + 1;
+ else if (off > freeme)
+ j = k;
+ else
+ i = j = k;
+ }
BUG_ON(off != freeme);
- BUG_ON(chunk->map[i] > 0);
- chunk->map[i] = -chunk->map[i];
- chunk->free_size += chunk->map[i];
+ p = chunk->map + i;
+ *p = off &= ~1;
+ chunk->free_size += (p[1] & ~1) - off;
- /* merge with previous? */
- if (i > 0 && chunk->map[i - 1] >= 0) {
- chunk->map[i - 1] += chunk->map[i];
- chunk->map_used--;
- memmove(&chunk->map[i], &chunk->map[i + 1],
- (chunk->map_used - i) * sizeof(chunk->map[0]));
- i--;
- }
/* merge with next? */
- if (i + 1 < chunk->map_used && chunk->map[i + 1] >= 0) {
- chunk->map[i] += chunk->map[i + 1];
- chunk->map_used--;
- memmove(&chunk->map[i + 1], &chunk->map[i + 2],
- (chunk->map_used - (i + 1)) * sizeof(chunk->map[0]));
+ if (!(p[1] & 1))
+ to_free++;
+ /* merge with previous? */
+ if (i > 0 && !(p[-1] & 1)) {
+ to_free++;
+ i--;
+ p--;
+ }
+ if (to_free) {
+ chunk->map_used -= to_free;
+ memmove(p + 1, p + 1 + to_free,
+ (chunk->map_used - i) * sizeof(chunk->map[0]));
}
- chunk->contig_hint = max(chunk->map[i], chunk->contig_hint);
+ chunk->contig_hint = max(chunk->map[i + 1] - chunk->map[i] - 1, chunk->contig_hint);
pcpu_chunk_relocate(chunk, oslot);
}
@@ -586,7 +597,9 @@
}
chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
- chunk->map[chunk->map_used++] = pcpu_unit_size;
+ chunk->map[0] = 0;
+ chunk->map[1] = pcpu_unit_size | 1;
+ chunk->map_used = 1;
INIT_LIST_HEAD(&chunk->list);
chunk->free_size = pcpu_unit_size;
@@ -682,6 +695,13 @@
unsigned long flags;
void __percpu *ptr;
+ /*
+ * We want the lowest bit of offset available for in-use/free
+ * indicator.
+ */
+ if (unlikely(align < 2))
+ align = 2;
+
if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
WARN(true, "illegal size (%zu) or align (%zu) for "
"percpu allocation\n", size, align);
@@ -1312,9 +1332,13 @@
}
schunk->contig_hint = schunk->free_size;
- schunk->map[schunk->map_used++] = -ai->static_size;
+ schunk->map[0] = 1;
+ schunk->map[1] = ai->static_size;
+ schunk->map_used = 1;
if (schunk->free_size)
- schunk->map[schunk->map_used++] = schunk->free_size;
+ schunk->map[++schunk->map_used] = 1 | (ai->static_size + schunk->free_size);
+ else
+ schunk->map[1] |= 1;
/* init dynamic chunk if necessary */
if (dyn_size) {
@@ -1327,8 +1351,10 @@
bitmap_fill(dchunk->populated, pcpu_unit_pages);
dchunk->contig_hint = dchunk->free_size = dyn_size;
- dchunk->map[dchunk->map_used++] = -pcpu_reserved_chunk_limit;
- dchunk->map[dchunk->map_used++] = dchunk->free_size;
+ dchunk->map[0] = 1;
+ dchunk->map[1] = pcpu_reserved_chunk_limit;
+ dchunk->map[2] = (pcpu_reserved_chunk_limit + dchunk->free_size) | 1;
+ dchunk->map_used = 2;
}
/* link the first chunk in */