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authorKent Overstreet <koverstreet@google.com>2013-04-26 10:58:39 +1000
committerKent Overstreet <koverstreet@google.com>2013-06-17 19:37:02 -0700
commit13be68b30881491e640bcc0b29c941155c1c0543 (patch)
treeb4bd4a21f1cd1e55944097b64a68d75ece9faea8
parentc583fc62bef569099498833f6b6356a1438c374f (diff)
aio: percpu reqs_available
See the previous patch ("aio: reqs_active -> reqs_available") for why we want to do this - this basically implements a per cpu allocator for reqs_available that doesn't actually allocate anything. Note that we need to increase the size of the ringbuffer we allocate, since a single thread won't necessarily be able to use all the reqs_available slots - some (up to about half) might be on other per cpu lists, unavailable for the current thread. We size the ringbuffer based on the nr_events userspace passed to io_setup(), so this is a slight behaviour change - but nr_events wasn't being used as a hard limit before, it was being rounded up to the next page before so this doesn't change the actual semantics. Signed-off-by: Kent Overstreet <koverstreet@google.com> Cc: Zach Brown <zab@redhat.com> Cc: Felipe Balbi <balbi@ti.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Mark Fasheh <mfasheh@suse.com> Cc: Joel Becker <jlbec@evilplan.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Jens Axboe <axboe@kernel.dk> Cc: Asai Thambi S P <asamymuthupa@micron.com> Cc: Selvan Mani <smani@micron.com> Cc: Sam Bradshaw <sbradshaw@micron.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Benjamin LaHaise <bcrl@kvack.org> Reviewed-by: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--fs/aio.c106
1 files changed, 99 insertions, 7 deletions
diff --git a/fs/aio.c b/fs/aio.c
index 8d5c1e3f7d83..879980ed37ca 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -26,6 +26,7 @@
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/mmu_context.h>
+#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/aio.h>
@@ -59,6 +60,10 @@ struct aio_ring {
#define AIO_RING_PAGES 8
+struct kioctx_cpu {
+ unsigned reqs_available;
+};
+
struct kioctx {
atomic_t users;
atomic_t dead;
@@ -67,6 +72,13 @@ struct kioctx {
unsigned long user_id;
struct hlist_node list;
+ struct __percpu kioctx_cpu *cpu;
+
+ /*
+ * For percpu reqs_available, number of slots we move to/from global
+ * counter at a time:
+ */
+ unsigned req_batch;
/*
* This is what userspace passed to io_setup(), it's not used for
* anything but counting against the global max_reqs quota.
@@ -94,6 +106,8 @@ struct kioctx {
* so we avoid overflowing it: it's decremented (if positive)
* when allocating a kiocb and incremented when the resulting
* io_event is pulled off the ringbuffer.
+ *
+ * We batch accesses to it with a percpu version.
*/
atomic_t reqs_available;
} ____cacheline_aligned_in_smp;
@@ -278,6 +292,8 @@ static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
static void free_ioctx_rcu(struct rcu_head *head)
{
struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
+
+ free_percpu(ctx->cpu);
kmem_cache_free(kioctx_cachep, ctx);
}
@@ -291,7 +307,7 @@ static void free_ioctx(struct kioctx *ctx)
struct aio_ring *ring;
struct io_event res;
struct kiocb *req;
- unsigned head, avail;
+ unsigned cpu, head, avail;
spin_lock_irq(&ctx->ctx_lock);
@@ -305,6 +321,13 @@ static void free_ioctx(struct kioctx *ctx)
spin_unlock_irq(&ctx->ctx_lock);
+ for_each_possible_cpu(cpu) {
+ struct kioctx_cpu *kcpu = per_cpu_ptr(ctx->cpu, cpu);
+
+ atomic_add(kcpu->reqs_available, &ctx->reqs_available);
+ kcpu->reqs_available = 0;
+ }
+
ring = kmap_atomic(ctx->ring_pages[0]);
head = ring->head;
kunmap_atomic(ring);
@@ -353,6 +376,18 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
struct kioctx *ctx;
int err = -ENOMEM;
+ /*
+ * We keep track of the number of available ringbuffer slots, to prevent
+ * overflow (reqs_available), and we also use percpu counters for this.
+ *
+ * So since up to half the slots might be on other cpu's percpu counters
+ * and unavailable, double nr_events so userspace sees what they
+ * expected: additionally, we move req_batch slots to/from percpu
+ * counters at a time, so make sure that isn't 0:
+ */
+ nr_events = max(nr_events, num_possible_cpus() * 4);
+ nr_events *= 2;
+
/* Prevent overflows */
if ((nr_events > (0x10000000U / sizeof(struct io_event))) ||
(nr_events > (0x10000000U / sizeof(struct kiocb)))) {
@@ -378,10 +413,16 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
INIT_LIST_HEAD(&ctx->active_reqs);
- if (aio_setup_ring(ctx) < 0)
+ ctx->cpu = alloc_percpu(struct kioctx_cpu);
+ if (!ctx->cpu)
goto out_freectx;
+ if (aio_setup_ring(ctx) < 0)
+ goto out_freepcpu;
+
atomic_set(&ctx->reqs_available, ctx->nr_events - 1);
+ ctx->req_batch = (ctx->nr_events - 1) / (num_possible_cpus() * 4);
+ BUG_ON(!ctx->req_batch);
/* limit the number of system wide aios */
spin_lock(&aio_nr_lock);
@@ -405,6 +446,8 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
out_cleanup:
err = -EAGAIN;
aio_free_ring(ctx);
+out_freepcpu:
+ free_percpu(ctx->cpu);
out_freectx:
kmem_cache_free(kioctx_cachep, ctx);
pr_debug("error allocating ioctx %d\n", err);
@@ -507,6 +550,52 @@ void exit_aio(struct mm_struct *mm)
}
}
+static void put_reqs_available(struct kioctx *ctx, unsigned nr)
+{
+ struct kioctx_cpu *kcpu;
+
+ preempt_disable();
+ kcpu = this_cpu_ptr(ctx->cpu);
+
+ kcpu->reqs_available += nr;
+ while (kcpu->reqs_available >= ctx->req_batch * 2) {
+ kcpu->reqs_available -= ctx->req_batch;
+ atomic_add(ctx->req_batch, &ctx->reqs_available);
+ }
+
+ preempt_enable();
+}
+
+static bool get_reqs_available(struct kioctx *ctx)
+{
+ struct kioctx_cpu *kcpu;
+ bool ret = false;
+
+ preempt_disable();
+ kcpu = this_cpu_ptr(ctx->cpu);
+
+ if (!kcpu->reqs_available) {
+ int old, avail = atomic_read(&ctx->reqs_available);
+
+ do {
+ if (avail < ctx->req_batch)
+ goto out;
+
+ old = avail;
+ avail = atomic_cmpxchg(&ctx->reqs_available,
+ avail, avail - ctx->req_batch);
+ } while (avail != old);
+
+ kcpu->reqs_available += ctx->req_batch;
+ }
+
+ ret = true;
+ kcpu->reqs_available--;
+out:
+ preempt_enable();
+ return ret;
+}
+
/* aio_get_req
* Allocate a slot for an aio request. Increments the ki_users count
* of the kioctx so that the kioctx stays around until all requests are
@@ -521,7 +610,7 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)
{
struct kiocb *req;
- if (atomic_dec_if_positive(&ctx->reqs_available) <= 0)
+ if (!get_reqs_available(ctx))
return NULL;
req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL|__GFP_ZERO);
@@ -530,10 +619,9 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)
atomic_set(&req->ki_users, 2);
req->ki_ctx = ctx;
-
return req;
out_put:
- atomic_inc(&ctx->reqs_available);
+ put_reqs_available(ctx, 1);
return NULL;
}
@@ -622,6 +710,10 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
*/
if (unlikely(xchg(&iocb->ki_cancel,
KIOCB_CANCELLED) == KIOCB_CANCELLED)) {
+ /*
+ * Can't use the percpu reqs_available here - could race with
+ * free_ioctx()
+ */
atomic_inc(&ctx->reqs_available);
/* Still need the wake_up in case free_ioctx is waiting */
goto put_rq;
@@ -760,7 +852,7 @@ static long aio_read_events_ring(struct kioctx *ctx,
pr_debug("%li h%u t%u\n", ret, head, ctx->tail);
- atomic_add(ret, &ctx->reqs_available);
+ put_reqs_available(ctx, ret);
out:
mutex_unlock(&ctx->ring_lock);
@@ -1144,7 +1236,7 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
aio_put_req(req); /* drop extra ref to req */
return 0;
out_put_req:
- atomic_inc(&ctx->reqs_available);
+ put_reqs_available(ctx, 1);
aio_put_req(req); /* drop extra ref to req */
aio_put_req(req); /* drop i/o ref to req */
return ret;