Re: [PATCH v9 1/5] lib: objpool added: ring-array based lockless MPMC
From: wuqiang.matt
Date: Thu Oct 12 2023 - 13:38:47 EST
On 2023/10/12 22:02, Masami Hiramatsu (Google) wrote:
Hi Wuqiang,
On Mon, 9 Oct 2023 17:23:34 +0800
wuqiang <wuqiang.matt@xxxxxxxxxxxxx> wrote:
Hello Masami,
Just got time for the new patch and got that ages[] was removed. ages[] is
introduced the way like 2-phase commit to keep consitency and must be kept.
Thinking of the following 2 cases that two cpu nodes are operating the same
objpool_slot simultaneously:
Case 1:
NODE 1: NODE 2:
push to an empty slot pop will get wrong value
try_cmpxchg_acquire(&slot->tail, &tail, next)
try_cmpxchg_release(&slot->head, &head, head + 1)
return slot->entries[head & slot->mask]
WRITE_ONCE(slot->entries[tail & slot->mask], obj)
Today, I rethink the algorithm.
For this case, we can just add a `commit` to the slot for committing the tail
commit instead of the ages[].
CPU1 CPU2
push to an empty slot pop from the same slot
commit = tail = slot->tail;
next = tail + 1;
try_cmpxchg_acquire(&slot->tail,
&tail, next);
while (head != commit) -> NG1
WRITE_ONCE(slot->entries[tail & slot->mask],
obj)
while (head != commit) -> NG2
WRITE_ONCE(&slot->commit, next);
while (head != commit) -> OK
try_cmpxchg_acquire(&slot->head,
&head, next);
return slot->entries[head & slot->mask]
So the NG1 and NG2 timing, the pop will fail.
This does not expect the nested "push" case because the reserve-commit block
will be interrupt disabled. This doesn't support NMI but that is OK.
If 2 push are performed in a row, slot->commit will be 'tail + 2', CPU2 won't
meet the condition "head == commit".
Since slot->commit' is always synced to slot->tail after a successful push,
should pop check "tail != commit" ? In this case when a push is ongoing with
the slot, pop() has to wait for its completion even if there are objects in
the same slot.
If we need to support such NMI or remove irq-disable, we can do following
(please remember the push operation only happens on the slot owned by that
CPU. So this is per-cpu process)
---
do {
commit = tail = slot->tail;
next = tail + 1;
} while (!try_cmpxchg_acquire(&slot->tail, &tail, next));
WRITE_ONCE(slot->entries[tail & slot->mask], obj);
// At this point, "commit == slot->tail - 1" in this nest level.
// Only outmost (non-nexted) case, "commit == slot->commit"
if (commit != slot->commit)
return; // do nothing. it must be updated by outmost one.
// catch up commit to tail.
do {
commit = READ_ONCE(slot->tail);
WRITE_ONCE(slot->commit, commit);
// note that someone can interrupt this loop too.
} while (commit != READ_ONCE(slot->tail));
---
Yes, I got you: push can only happen on local node and the first try has the
right to extend 'commit'. It does resolve nested push attempts, and preemption
must be disabled.
The overflow/ABA issue can still happen if the cpu is being interrupted for
long time.
For the rethook this may be too much.
Thank you,
Case 2:
NODE 1: NODE 2
push to slot w/ 1 obj pop will get wrong value
try_cmpxchg_release(&slot->head, &head, head + 1)
try_cmpxchg_acquire(&slot->tail, &tail, next)
WRITE_ONCE(slot->entries[tail & slot->mask], obj)
return slot->entries[head & slot->mask]
The pre-condition should be: CPU 1 tries to push to a full slot, in this case
tail = head + capacity but tail & mask == head & mask
Regards,
wuqiang
On 2023/9/25 17:42, Masami Hiramatsu (Google) wrote:
Hi Wuqiang,
On Tue, 5 Sep 2023 09:52:51 +0800
"wuqiang.matt" <wuqiang.matt@xxxxxxxxxxxxx> wrote:
The object pool is a scalable implementaion of high performance queue
for object allocation and reclamation, such as kretprobe instances.
With leveraging percpu ring-array to mitigate the hot spot of memory
contention, it could deliver near-linear scalability for high parallel
scenarios. The objpool is best suited for following cases:
1) Memory allocation or reclamation are prohibited or too expensive
2) Consumers are of different priorities, such as irqs and threads
Limitations:
1) Maximum objects (capacity) is determined during pool initializing
and can't be modified (extended) after objpool creation
2) The memory of objects won't be freed until objpool is finalized
3) Object allocation (pop) may fail after trying all cpu slots
I made a simplifying patch on this by (mainly) removing ages array.
I also rename local variable to use more readable names, like slot,
pool, and obj.
Here the results which I run the test_objpool.ko.
Original:
[ 50.500235] Summary of testcases:
[ 50.503139] duration: 1027135us hits: 30628293 miss: 0 sync: percpu objpool
[ 50.510416] duration: 1047977us hits: 30453023 miss: 0 sync: percpu objpool from vmalloc
[ 50.517421] duration: 1047098us hits: 31145034 miss: 0 sync & hrtimer: percpu objpool
[ 50.524671] duration: 1053233us hits: 30919640 miss: 0 sync & hrtimer: percpu objpool from vmalloc
[ 50.531382] duration: 1055822us hits: 3407221 miss: 830219 sync overrun: percpu objpool
[ 50.538135] duration: 1055998us hits: 3404624 miss: 854160 sync overrun: percpu objpool from vmalloc
[ 50.546686] duration: 1046104us hits: 19464798 miss: 0 async: percpu objpool
[ 50.552989] duration: 1033054us hits: 18957836 miss: 0 async: percpu objpool from vmalloc
[ 50.560289] duration: 1041778us hits: 33806868 miss: 0 async & hrtimer: percpu objpool
[ 50.567425] duration: 1048901us hits: 34211860 miss: 0 async & hrtimer: percpu objpool from vmalloc
Simplified:
[ 48.393236] Summary of testcases:
[ 48.395384] duration: 1013002us hits: 29661448 miss: 0 sync: percpu objpool
[ 48.400351] duration: 1057231us hits: 31035578 miss: 0 sync: percpu objpool from vmalloc
[ 48.405660] duration: 1043196us hits: 30546652 miss: 0 sync & hrtimer: percpu objpool
[ 48.411216] duration: 1047128us hits: 30601306 miss: 0 sync & hrtimer: percpu objpool from vmalloc
[ 48.417231] duration: 1051695us hits: 3468287 miss: 892881 sync overrun: percpu objpool
[ 48.422405] duration: 1054003us hits: 3549491 miss: 898141 sync overrun: percpu objpool from vmalloc
[ 48.428425] duration: 1052946us hits: 19005228 miss: 0 async: percpu objpool
[ 48.433597] duration: 1051757us hits: 19670866 miss: 0 async: percpu objpool from vmalloc
[ 48.439280] duration: 1042951us hits: 37135332 miss: 0 async & hrtimer: percpu objpool
[ 48.445085] duration: 1029803us hits: 37093248 miss: 0 async & hrtimer: percpu objpool from vmalloc
Can you test it too?
Thanks,
From f1f442ff653e329839e5452b8b88463a80a12ff3 Mon Sep 17 00:00:00 2001
From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Date: Mon, 25 Sep 2023 16:07:12 +0900
Subject: [PATCH] objpool: Simplify objpool by removing ages array
Simplify the objpool code by removing ages array from per-cpu slot.
It chooses enough big capacity (which is a rounded up power of 2 value
of nr_objects + 1) for the entries array, the tail never catch up to
the head in per-cpu slot. Thus tail == head means the slot is empty.
This also uses consistent local variable names for pool, slot and obj.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
include/linux/objpool.h | 61 ++++----
lib/objpool.c | 310 ++++++++++++++++------------------------
2 files changed, 147 insertions(+), 224 deletions(-)
diff --git a/include/linux/objpool.h b/include/linux/objpool.h
index 33c832216b98..ecd5ecaffcd3 100644
--- a/include/linux/objpool.h
+++ b/include/linux/objpool.h
@@ -38,33 +38,23 @@
* struct objpool_slot - percpu ring array of objpool
* @head: head of the local ring array (to retrieve at)
* @tail: tail of the local ring array (to append at)
- * @bits: log2 of capacity (for bitwise operations)
- * @mask: capacity - 1
+ * @mask: capacity of entries - 1
+ * @entries: object entries on this slot.
*
* Represents a cpu-local array-based ring buffer, its size is specialized
* during initialization of object pool. The percpu objpool slot is to be
* allocated from local memory for NUMA system, and to be kept compact in
- * continuous memory: ages[] is stored just after the body of objpool_slot,
- * and then entries[]. ages[] describes revision of each item, solely used
- * to avoid ABA; entries[] contains pointers of the actual objects
- *
- * Layout of objpool_slot in memory:
- *
- * 64bit:
- * 4 8 12 16 32 64
- * | head | tail | bits | mask | ages[4] | ents[4]: (8 * 4) | objects
- *
- * 32bit:
- * 4 8 12 16 32 48 64
- * | head | tail | bits | mask | ages[4] | ents[4] | unused | objects
+ * continuous memory: CPU assigned number of objects are stored just after
+ * the body of objpool_slot.
*
*/
struct objpool_slot {
- uint32_t head;
- uint32_t tail;
- uint32_t bits;
- uint32_t mask;
-} __packed;
+ uint32_t head;
+ uint32_t tail;
+ uint32_t mask;
+ uint32_t dummyr;
+ void * entries[];
+};
struct objpool_head;
@@ -82,12 +72,11 @@ typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
* @obj_size: object & element size
* @nr_objs: total objs (to be pre-allocated)
* @nr_cpus: nr_cpu_ids
- * @capacity: max objects per cpuslot
+ * @capacity: max objects on percpu slot
* @gfp: gfp flags for kmalloc & vmalloc
* @ref: refcount for objpool
* @flags: flags for objpool management
* @cpu_slots: array of percpu slots
- * @slot_sizes: size in bytes of slots
* @release: resource cleanup callback
* @context: caller-provided context
*/
@@ -100,7 +89,6 @@ struct objpool_head {
refcount_t ref;
unsigned long flags;
struct objpool_slot **cpu_slots;
- int *slot_sizes;
objpool_fini_cb release;
void *context;
};
@@ -108,9 +96,12 @@ struct objpool_head {
#define OBJPOOL_FROM_VMALLOC (0x800000000) /* objpool allocated from vmalloc area */
#define OBJPOOL_HAVE_OBJECTS (0x400000000) /* objects allocated along with objpool */
+#define OBJPOOL_NR_OBJECT_MAX (1 << 24)
+#define OBJPOOL_OBJECT_SIZE_MAX (1 << 16)
+
/**
* objpool_init() - initialize objpool and pre-allocated objects
- * @head: the object pool to be initialized, declared by caller
+ * @pool: the object pool to be initialized, declared by caller
* @nr_objs: total objects to be pre-allocated by this object pool
* @object_size: size of an object (should be > 0)
* @gfp: flags for memory allocation (via kmalloc or vmalloc)
@@ -128,47 +119,47 @@ struct objpool_head {
* pop (object allocation) or do clearance before each push (object
* reclamation).
*/
-int objpool_init(struct objpool_head *head, int nr_objs, int object_size,
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
gfp_t gfp, void *context, objpool_init_obj_cb objinit,
objpool_fini_cb release);
/**
* objpool_pop() - allocate an object from objpool
- * @head: object pool
+ * @pool: object pool
*
* return value: object ptr or NULL if failed
*/
-void *objpool_pop(struct objpool_head *head);
+void *objpool_pop(struct objpool_head *pool);
/**
* objpool_push() - reclaim the object and return back to objpool
* @obj: object ptr to be pushed to objpool
- * @head: object pool
+ * @pool: object pool
*
* return: 0 or error code (it fails only when user tries to push
* the same object multiple times or wrong "objects" into objpool)
*/
-int objpool_push(void *obj, struct objpool_head *head);
+int objpool_push(void *obj, struct objpool_head *pool);
/**
* objpool_drop() - discard the object and deref objpool
* @obj: object ptr to be discarded
- * @head: object pool
+ * @pool: object pool
*
* return: 0 if objpool was released or error code
*/
-int objpool_drop(void *obj, struct objpool_head *head);
+int objpool_drop(void *obj, struct objpool_head *pool);
/**
* objpool_free() - release objpool forcely (all objects to be freed)
- * @head: object pool to be released
+ * @pool: object pool to be released
*/
-void objpool_free(struct objpool_head *head);
+void objpool_free(struct objpool_head *pool);
/**
* objpool_fini() - deref object pool (also releasing unused objects)
- * @head: object pool to be dereferenced
+ * @pool: object pool to be dereferenced
*/
-void objpool_fini(struct objpool_head *head);
+void objpool_fini(struct objpool_head *pool);
#endif /* _LINUX_OBJPOOL_H */
diff --git a/lib/objpool.c b/lib/objpool.c
index 22e752371820..f8e8f70d7253 100644
--- a/lib/objpool.c
+++ b/lib/objpool.c
@@ -15,104 +15,55 @@
* Copyright: wuqiang.matt@xxxxxxxxxxxxx
*/
-#define SLOT_AGES(s) ((uint32_t *)((char *)(s) + sizeof(struct objpool_slot)))
-#define SLOT_ENTS(s) ((void **)((char *)(s) + sizeof(struct objpool_slot) + \
- (sizeof(uint32_t) << (s)->bits)))
-#define SLOT_OBJS(s) ((void *)((char *)(s) + sizeof(struct objpool_slot) + \
- ((sizeof(uint32_t) + sizeof(void *)) << (s)->bits)))
-#define SLOT_CORE(n) cpumask_nth((n) % num_possible_cpus(), cpu_possible_mask)
-
-/* compute the suitable num of objects to be managed per slot */
-static int objpool_nobjs(int size)
-{
- return rounddown_pow_of_two((size - sizeof(struct objpool_slot)) /
- (sizeof(uint32_t) + sizeof(void *)));
-}
-
/* allocate and initialize percpu slots */
static int
-objpool_init_percpu_slots(struct objpool_head *head, int nobjs,
- void *context, objpool_init_obj_cb objinit)
+objpool_init_percpu_slots(struct objpool_head *pool, void *context,
+ objpool_init_obj_cb objinit)
{
- int i, j, n, size, objsz, cpu = 0, nents = head->capacity;
-
- /* aligned object size by sizeof(void *) */
- objsz = ALIGN(head->obj_size, sizeof(void *));
- /* shall we allocate objects along with percpu-slot */
- if (objsz)
- head->flags |= OBJPOOL_HAVE_OBJECTS;
-
- /* vmalloc is used in default to allocate percpu-slots */
- if (!(head->gfp & GFP_ATOMIC))
- head->flags |= OBJPOOL_FROM_VMALLOC;
-
- for (i = 0; i < head->nr_cpus; i++) {
- struct objpool_slot *os;
+ int i, j, n, size, slot_size, cpu_count = 0;
+ struct objpool_slot *slot;
+ for (i = 0; i < pool->nr_cpus; i++) {
/* skip the cpus which could never be present */
if (!cpu_possible(i))
continue;
/* compute how many objects to be managed by this slot */
- n = nobjs / num_possible_cpus();
- if (cpu < (nobjs % num_possible_cpus()))
+ n = pool->nr_objs / num_possible_cpus();
+ if (cpu_count < (pool->nr_objs % num_possible_cpus()))
n++;
- size = sizeof(struct objpool_slot) + sizeof(void *) * nents +
- sizeof(uint32_t) * nents + objsz * n;
+ cpu_count++;
+
+ slot_size = struct_size(slot, entries, pool->capacity);
+ size = slot_size + pool->obj_size * n;
/*
* here we allocate percpu-slot & objects together in a single
- * allocation, taking advantage of warm caches and TLB hits as
- * vmalloc always aligns the request size to pages
+ * allocation, taking advantage on NUMA.
*/
- if (head->flags & OBJPOOL_FROM_VMALLOC)
- os = __vmalloc_node(size, sizeof(void *), head->gfp,
+ if (pool->flags & OBJPOOL_FROM_VMALLOC)
+ slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
cpu_to_node(i), __builtin_return_address(0));
else
- os = kmalloc_node(size, head->gfp, cpu_to_node(i));
- if (!os)
+ slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+ if (!slot)
return -ENOMEM;
/* initialize percpu slot for the i-th slot */
- memset(os, 0, size);
- os->bits = ilog2(head->capacity);
- os->mask = head->capacity - 1;
- head->cpu_slots[i] = os;
- head->slot_sizes[i] = size;
- cpu = cpu + 1;
-
- /*
- * manually set head & tail to avoid possible conflict:
- * We assume that the head item is ready for retrieval
- * iff head is equal to ages[head & mask]. but ages is
- * initialized as 0, so in view of the caller of pop(),
- * the 1st item (0th) is always ready, but the reality
- * could be: push() is stalled before the final update,
- * thus the item being inserted will be lost forever
- */
- os->head = os->tail = head->capacity;
-
- if (!objsz)
- continue;
+ memset(slot, 0, size);
+ slot->mask = pool->capacity - 1;
+ pool->cpu_slots[i] = slot;
for (j = 0; j < n; j++) {
- uint32_t *ages = SLOT_AGES(os);
- void **ents = SLOT_ENTS(os);
- void *obj = SLOT_OBJS(os) + j * objsz;
- uint32_t ie = os->tail & os->mask;
+ void *obj = (void *)slot + slot_size + pool->obj_size * j;
- /* perform object initialization */
if (objinit) {
int rc = objinit(obj, context);
if (rc)
return rc;
}
-
- /* add obj into the ring array */
- ents[ie] = obj;
- ages[ie] = os->tail;
- os->tail++;
- head->nr_objs++;
+ slot->entries[j] = obj;
+ slot->tail++;
}
}
@@ -120,164 +71,135 @@ objpool_init_percpu_slots(struct objpool_head *head, int nobjs,
}
/* cleanup all percpu slots of the object pool */
-static void objpool_fini_percpu_slots(struct objpool_head *head)
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
{
int i;
- if (!head->cpu_slots)
+ if (!pool->cpu_slots)
return;
- for (i = 0; i < head->nr_cpus; i++) {
- if (!head->cpu_slots[i])
- continue;
- if (head->flags & OBJPOOL_FROM_VMALLOC)
- vfree(head->cpu_slots[i]);
- else
- kfree(head->cpu_slots[i]);
- }
- kfree(head->cpu_slots);
- head->cpu_slots = NULL;
- head->slot_sizes = NULL;
+ for (i = 0; i < pool->nr_cpus; i++)
+ kvfree(pool->cpu_slots[i]);
+ kfree(pool->cpu_slots);
}
/* initialize object pool and pre-allocate objects */
-int objpool_init(struct objpool_head *head, int nr_objs, int object_size,
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
gfp_t gfp, void *context, objpool_init_obj_cb objinit,
objpool_fini_cb release)
{
int nents, rc;
/* check input parameters */
- if (nr_objs <= 0 || object_size <= 0)
+ if (nr_objs <= 0 || object_size <= 0 ||
+ nr_objs > OBJPOOL_NR_OBJECT_MAX || object_size > OBJPOOL_OBJECT_SIZE_MAX)
+ return -EINVAL;
+
+ /* Align up to unsigned long size */
+ object_size = ALIGN(object_size, sizeof(unsigned long));
+
+ /*
+ * To avoid filling up the entries array in the per-cpu slot,
+ * use the power of 2 which is more than N + 1. Thus, the tail never
+ * catch up to the pool, and able to use pool/tail as the sequencial
+ * number.
+ */
+ nents = roundup_pow_of_two(nr_objs + 1);
+ if (!nents)
return -EINVAL;
- /* calculate percpu slot size (rounded to pow of 2) */
- nents = max_t(int, roundup_pow_of_two(nr_objs),
- objpool_nobjs(L1_CACHE_BYTES));
-
- /* initialize objpool head */
- memset(head, 0, sizeof(struct objpool_head));
- head->nr_cpus = nr_cpu_ids;
- head->obj_size = object_size;
- head->capacity = nents;
- head->gfp = gfp & ~__GFP_ZERO;
- head->context = context;
- head->release = release;
-
- /* allocate array for percpu slots */
- head->cpu_slots = kzalloc(head->nr_cpus * sizeof(void *) +
- head->nr_cpus * sizeof(int), head->gfp);
- if (!head->cpu_slots)
+ /* initialize objpool pool */
+ memset(pool, 0, sizeof(struct objpool_head));
+ pool->nr_cpus = nr_cpu_ids;
+ pool->obj_size = object_size;
+ pool->nr_objs = nr_objs;
+ /* just prevent to fullfill the per-cpu ring array */
+ pool->capacity = nents;
+ pool->gfp = gfp & ~__GFP_ZERO;
+ pool->context = context;
+ pool->release = release;
+ /* vmalloc is used in default to allocate percpu-slots */
+ if (!(pool->gfp & GFP_ATOMIC))
+ pool->flags |= OBJPOOL_FROM_VMALLOC;
+
+ pool->cpu_slots = kzalloc(pool->nr_cpus * sizeof(void *), pool->gfp);
+ if (!pool->cpu_slots)
return -ENOMEM;
- head->slot_sizes = (int *)&head->cpu_slots[head->nr_cpus];
/* initialize per-cpu slots */
- rc = objpool_init_percpu_slots(head, nr_objs, context, objinit);
+ rc = objpool_init_percpu_slots(pool, context, objinit);
if (rc)
- objpool_fini_percpu_slots(head);
+ objpool_fini_percpu_slots(pool);
else
- refcount_set(&head->ref, nr_objs + 1);
+ refcount_set(&pool->ref, nr_objs + 1);
return rc;
}
EXPORT_SYMBOL_GPL(objpool_init);
/* adding object to slot, abort if the slot was already full */
-static inline int objpool_try_add_slot(void *obj, struct objpool_slot *os)
+static inline int objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
{
- uint32_t *ages = SLOT_AGES(os);
- void **ents = SLOT_ENTS(os);
- uint32_t head, tail;
+ struct objpool_slot *slot = pool->cpu_slots[cpu];
+ uint32_t tail, next;
do {
- /* perform memory loading for both head and tail */
- head = READ_ONCE(os->head);
- tail = READ_ONCE(os->tail);
- /* just abort if slot is full */
- if (tail - head > os->mask)
- return -ENOENT;
- /* try to extend tail by 1 using CAS to avoid races */
- if (try_cmpxchg_acquire(&os->tail, &tail, tail + 1))
- break;
- } while (1);
+ uint32_t head = READ_ONCE(slot->head);
- /* the tail-th of slot is reserved for the given obj */
- WRITE_ONCE(ents[tail & os->mask], obj);
- /* update epoch id to make this object available for pop() */
- smp_store_release(&ages[tail & os->mask], tail);
+ tail = READ_ONCE(slot->tail);
+ next = tail + 1;
+
+ /* This must never happen because capacity >= N + 1 */
+ if (WARN_ON_ONCE((next > head && next - head > pool->nr_objs) ||
+ (next < head && next > head + pool->nr_objs)))
+ return -EINVAL;
+
+ } while (!try_cmpxchg_acquire(&slot->tail, &tail, next));
+
+ WRITE_ONCE(slot->entries[tail & slot->mask], obj);
return 0;
}
/* reclaim an object to object pool */
-int objpool_push(void *obj, struct objpool_head *oh)
+int objpool_push(void *obj, struct objpool_head *pool)
{
unsigned long flags;
- int cpu, rc;
+ int rc;
/* disable local irq to avoid preemption & interruption */
raw_local_irq_save(flags);
- cpu = raw_smp_processor_id();
- do {
- rc = objpool_try_add_slot(obj, oh->cpu_slots[cpu]);
- if (!rc)
- break;
- cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
- } while (1);
+ rc = objpool_try_add_slot(obj, pool, raw_smp_processor_id());
raw_local_irq_restore(flags);
return rc;
}
EXPORT_SYMBOL_GPL(objpool_push);
-/* drop the allocated object, rather reclaim it to objpool */
-int objpool_drop(void *obj, struct objpool_head *head)
-{
- if (!obj || !head)
- return -EINVAL;
-
- if (refcount_dec_and_test(&head->ref)) {
- objpool_free(head);
- return 0;
- }
-
- return -EAGAIN;
-}
-EXPORT_SYMBOL_GPL(objpool_drop);
-
/* try to retrieve object from slot */
-static inline void *objpool_try_get_slot(struct objpool_slot *os)
+static inline void *objpool_try_get_slot(struct objpool_slot *slot)
{
- uint32_t *ages = SLOT_AGES(os);
- void **ents = SLOT_ENTS(os);
/* do memory load of head to local head */
- uint32_t head = smp_load_acquire(&os->head);
+ uint32_t head = smp_load_acquire(&slot->head);
/* loop if slot isn't empty */
- while (head != READ_ONCE(os->tail)) {
- uint32_t id = head & os->mask, prev = head;
+ while (head != READ_ONCE(slot->tail)) {
/* do prefetching of object ents */
- prefetch(&ents[id]);
-
- /* check whether this item was ready for retrieval */
- if (smp_load_acquire(&ages[id]) == head) {
- /* node must have been udpated by push() */
- void *node = READ_ONCE(ents[id]);
- /* commit and move forward head of the slot */
- if (try_cmpxchg_release(&os->head, &head, head + 1))
- return node;
- /* head was already updated by others */
- }
+ prefetch(&slot->entries[head & slot->mask]);
+
+ /* commit and move forward head of the slot */
+ if (try_cmpxchg_release(&slot->head, &head, head + 1))
+ /*
+ * TBD: check overwrap the tail/head counter and warn
+ * if it is broken. But this happens only if this
+ * process slows down a lot and another CPU updates
+ * the haed/tail just 2^32 + 1 times, and this slot
+ * is empty.
+ */
+ return slot->entries[head & slot->mask];
/* re-load head from memory and continue trying */
- head = READ_ONCE(os->head);
- /*
- * head stays unchanged, so it's very likely there's an
- * ongoing push() on other cpu nodes but yet not update
- * ages[] to mark it's completion
- */
- if (head == prev)
- break;
+ head = READ_ONCE(slot->head);
}
return NULL;
@@ -307,32 +229,42 @@ void *objpool_pop(struct objpool_head *head)
EXPORT_SYMBOL_GPL(objpool_pop);
/* release whole objpool forcely */
-void objpool_free(struct objpool_head *head)
+void objpool_free(struct objpool_head *pool)
{
- if (!head->cpu_slots)
+ if (!pool->cpu_slots)
return;
/* release percpu slots */
- objpool_fini_percpu_slots(head);
+ objpool_fini_percpu_slots(pool);
/* call user's cleanup callback if provided */
- if (head->release)
- head->release(head, head->context);
+ if (pool->release)
+ pool->release(pool, pool->context);
}
EXPORT_SYMBOL_GPL(objpool_free);
-/* drop unused objects and defref objpool for releasing */
-void objpool_fini(struct objpool_head *head)
+/* drop the allocated object, rather reclaim it to objpool */
+int objpool_drop(void *obj, struct objpool_head *pool)
{
- void *nod;
+ if (!obj || !pool)
+ return -EINVAL;
- do {
- /* grab object from objpool and drop it */
- nod = objpool_pop(head);
+ if (refcount_dec_and_test(&pool->ref)) {
+ objpool_free(pool);
+ return 0;
+ }
+
+ return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(objpool_drop);
+
+/* drop unused objects and defref objpool for releasing */
+void objpool_fini(struct objpool_head *pool)
+{
+ void *obj;
- /* drop the extra ref of objpool */
- if (refcount_dec_and_test(&head->ref))
- objpool_free(head);
- } while (nod);
+ /* grab object from objpool and drop it */
+ while ((obj = objpool_pop(pool)))
+ objpool_drop(obj, pool);
}
EXPORT_SYMBOL_GPL(objpool_fini);