percpu: make sure chunk->map array has available space
An allocation attempt may require extending chunk->map array which
requires GFP_KERNEL context which isn't available for atomic
allocations. This patch ensures that chunk->map array usually keeps
some amount of available space by directly allocating buffer space
during GFP_KERNEL allocations and scheduling async extension during
atomic ones. This should make atomic allocation failures from map
space exhaustion rare.
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/percpu.c b/mm/percpu.c
index c52b931..546ced0 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -76,6 +76,8 @@
#define PCPU_SLOT_BASE_SHIFT 5 /* 1-31 shares the same slot */
#define PCPU_DFL_MAP_ALLOC 16 /* start a map with 16 ents */
+#define PCPU_ATOMIC_MAP_MARGIN_LOW 32
+#define PCPU_ATOMIC_MAP_MARGIN_HIGH 64
#ifdef CONFIG_SMP
/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
@@ -102,9 +104,12 @@
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 before the sentry */
int map_alloc; /* # of map entries allocated */
int *map; /* allocation map */
+ struct work_struct map_extend_work;/* async ->map[] extension */
+
void *data; /* chunk data */
int first_free; /* no free below this */
bool immutable; /* no [de]population allowed */
@@ -318,9 +323,14 @@
/**
* pcpu_need_to_extend - determine whether chunk area map needs to be extended
* @chunk: chunk of interest
+ * @is_atomic: the allocation context
*
- * Determine whether area map of @chunk needs to be extended to
- * accommodate a new allocation.
+ * Determine whether area map of @chunk needs to be extended. If
+ * @is_atomic, only the amount necessary for a new allocation is
+ * considered; however, async extension is scheduled if the left amount is
+ * low. If !@is_atomic, it aims for more empty space. Combined, this
+ * ensures that the map is likely to have enough available space to
+ * accomodate atomic allocations which can't extend maps directly.
*
* CONTEXT:
* pcpu_lock.
@@ -329,15 +339,25 @@
* New target map allocation length if extension is necessary, 0
* otherwise.
*/
-static int pcpu_need_to_extend(struct pcpu_chunk *chunk)
+static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic)
{
- int new_alloc;
+ int margin, new_alloc;
- if (chunk->map_alloc >= chunk->map_used + 3)
+ if (is_atomic) {
+ margin = 3;
+
+ if (chunk->map_alloc <
+ chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW)
+ schedule_work(&chunk->map_extend_work);
+ } else {
+ margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;
+ }
+
+ if (chunk->map_alloc >= chunk->map_used + margin)
return 0;
new_alloc = PCPU_DFL_MAP_ALLOC;
- while (new_alloc < chunk->map_used + 3)
+ while (new_alloc < chunk->map_used + margin)
new_alloc *= 2;
return new_alloc;
@@ -394,6 +414,20 @@
return 0;
}
+static void pcpu_map_extend_workfn(struct work_struct *work)
+{
+ struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk,
+ map_extend_work);
+ int new_alloc;
+
+ spin_lock_irq(&pcpu_lock);
+ new_alloc = pcpu_need_to_extend(chunk, false);
+ spin_unlock_irq(&pcpu_lock);
+
+ if (new_alloc)
+ pcpu_extend_area_map(chunk, new_alloc);
+}
+
/**
* pcpu_fit_in_area - try to fit the requested allocation in a candidate area
* @chunk: chunk the candidate area belongs to
@@ -647,6 +681,7 @@
chunk->map_used = 1;
INIT_LIST_HEAD(&chunk->list);
+ INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn);
chunk->free_size = pcpu_unit_size;
chunk->contig_hint = pcpu_unit_size;
@@ -767,7 +802,7 @@
goto fail_unlock;
}
- while ((new_alloc = pcpu_need_to_extend(chunk))) {
+ while ((new_alloc = pcpu_need_to_extend(chunk, is_atomic))) {
spin_unlock_irqrestore(&pcpu_lock, flags);
if (is_atomic ||
pcpu_extend_area_map(chunk, new_alloc) < 0) {
@@ -792,7 +827,7 @@
if (size > chunk->contig_hint)
continue;
- new_alloc = pcpu_need_to_extend(chunk);
+ new_alloc = pcpu_need_to_extend(chunk, is_atomic);
if (new_alloc) {
if (is_atomic)
continue;
@@ -1418,6 +1453,7 @@
*/
schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
INIT_LIST_HEAD(&schunk->list);
+ INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn);
schunk->base_addr = base_addr;
schunk->map = smap;
schunk->map_alloc = ARRAY_SIZE(smap);
@@ -1446,6 +1482,7 @@
if (dyn_size) {
dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
INIT_LIST_HEAD(&dchunk->list);
+ INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn);
dchunk->base_addr = base_addr;
dchunk->map = dmap;
dchunk->map_alloc = ARRAY_SIZE(dmap);