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percpu: make sure chunk->map array has available space

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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>
This commit is contained in:
Tejun Heo 2014-09-02 14:46:05 -04:00
parent 5835d96e9c
commit 9c824b6a17
1 changed files with 45 additions and 8 deletions
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53
mm/percpu.c
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@ -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 @@ struct pcpu_chunk {
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 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
/**
* 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 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
* 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 @@ out_unlock:
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 @@ static struct pcpu_chunk *pcpu_alloc_chunk(void)
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 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
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 @@ restart:
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 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
*/
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 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
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);