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Subject[PATCH 21/32] aio: reqs_active -> reqs_available
Date
The number of outstanding kiocbs is one of the few shared things left
that has to be touched for every kiocb - it'd be nice to make it percpu.

We can make it per cpu by treating it like an allocation problem: we
have a maximum number of kiocbs that can be outstanding (i.e. slots) -
then we just allocate and free slots, and we know how to write per cpu
allocators.

So as prep work for that, we convert reqs_active to reqs_available.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
---
fs/aio.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index fa87732..d384eb2 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -82,7 +82,7 @@ struct kioctx {
struct work_struct rcu_work;

struct {
- atomic_t reqs_active;
+ atomic_t reqs_available;
} ____cacheline_aligned;

struct {
@@ -286,17 +286,17 @@ static void free_ioctx(struct kioctx *ctx)
head = ring->head;
kunmap_atomic(ring);

- while (atomic_read(&ctx->reqs_active) > 0) {
+ while (atomic_read(&ctx->reqs_available) < ctx->nr) {
wait_event(ctx->wait, head != ctx->tail);

avail = (head < ctx->tail ? ctx->tail : ctx->nr) - head;

- atomic_sub(avail, &ctx->reqs_active);
+ atomic_add(avail, &ctx->reqs_available);
head += avail;
head %= ctx->nr;
}

- WARN_ON(atomic_read(&ctx->reqs_active) < 0);
+ WARN_ON(atomic_read(&ctx->reqs_available) > ctx->nr);

aio_free_ring(ctx);

@@ -360,6 +360,8 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
if (aio_setup_ring(ctx) < 0)
goto out_freectx;

+ atomic_set(&ctx->reqs_available, ctx->nr);
+
/* limit the number of system wide aios */
spin_lock(&aio_nr_lock);
if (aio_nr + nr_events > aio_max_nr ||
@@ -462,7 +464,7 @@ void exit_aio(struct mm_struct *mm)
"exit_aio:ioctx still alive: %d %d %d\n",
atomic_read(&ctx->users),
atomic_read(&ctx->dead),
- atomic_read(&ctx->reqs_active));
+ atomic_read(&ctx->reqs_available));
/*
* We don't need to bother with munmap() here -
* exit_mmap(mm) is coming and it'll unmap everything.
@@ -494,12 +496,9 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)
{
struct kiocb *req;

- if (atomic_read(&ctx->reqs_active) >= ctx->nr)
+ if (atomic_dec_if_positive(&ctx->reqs_available) <= 0)
return NULL;

- if (atomic_inc_return(&ctx->reqs_active) > ctx->nr)
- goto out_put;
-
req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL|__GFP_ZERO);
if (unlikely(!req))
goto out_put;
@@ -509,7 +508,7 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)

return req;
out_put:
- atomic_dec(&ctx->reqs_active);
+ atomic_inc(&ctx->reqs_available);
return NULL;
}

@@ -580,7 +579,7 @@ void aio_complete(struct kiocb *iocb, long res, long res2)

/*
* Take rcu_read_lock() in case the kioctx is being destroyed, as we
- * need to issue a wakeup after decrementing reqs_active.
+ * need to issue a wakeup after incrementing reqs_available.
*/
rcu_read_lock();

@@ -598,7 +597,7 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
*/
if (unlikely(xchg(&iocb->ki_cancel,
KIOCB_CANCELLED) == KIOCB_CANCELLED)) {
- atomic_dec(&ctx->reqs_active);
+ atomic_inc(&ctx->reqs_available);
/* Still need the wake_up in case free_ioctx is waiting */
goto put_rq;
}
@@ -738,7 +737,7 @@ static int aio_read_events_ring(struct kioctx *ctx,

pr_debug("%d h%u t%u\n", ret, head, ctx->tail);

- atomic_sub(ret, &ctx->reqs_active);
+ atomic_add(ret, &ctx->reqs_available);
out:
mutex_unlock(&ctx->ring_lock);

@@ -1157,7 +1156,7 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
return 0;

out_put_req:
- atomic_dec(&ctx->reqs_active);
+ atomic_inc(&ctx->reqs_available);
aio_put_req(req); /* drop extra ref to req */
aio_put_req(req); /* drop i/o ref to req */
return ret;
--
1.7.12


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