[PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue()

Jens Axboe
2009-06-26T09:06:14Z

Setup an emergency fallback cfqq that we allocate at IO scheduler init
time. If the slab allocation fails in cfq_find_alloc_queue(), we'll just
punt IO to that cfqq instead. This ensures that cfq_find_alloc_queue()
never fails without having to ensure free memory.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
block/cfq-iosched.c | 124 +++++++++++++++++++++++++++-----------------------
1 files changed, 67 insertions(+), 57 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c760ae7..91e7e0b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -71,6 +71,51 @@ struct cfq_rb_root {
#define CFQ_RB_ROOT (struct cfq_rb_root) { RB_ROOT, NULL, }

/*
+ * Per process-grouping structure
+ */
+struct cfq_queue {
+ /* reference count */
+ atomic_t ref;
+ /* various state flags, see below */
+ unsigned int flags;
+ /* parent cfq_data */
+ struct cfq_data *cfqd;
+ /* service_tree member */
+ struct rb_node rb_node;
+ /* service_tree key */
+ unsigned long rb_key;
+ /* prio tree member */
+ struct rb_node p_node;
+ /* prio tree root we belong to, if any */
+ struct rb_root *p_root;
+ /* sorted list of pending requests */
+ struct rb_root sort_list;
+ /* if fifo isn't expired, next request to serve */
+ struct request *next_rq;
+ /* requests queued in sort_list */
+ int queued[2];
+ /* currently allocated requests */
+ int allocated[2];
+ /* fifo list of requests in sort_list */
+ struct list_head fifo;
+
+ unsigned long slice_end;
+ long slice_resid;
+ unsigned int slice_dispatch;
+
+ /* pending metadata requests */
+ int meta_pending;
+ /* number of requests that are on the dispatch list or inside driver */
+ int dispatched;
+
+ /* io prio of this group */
+ unsigned short ioprio, org_ioprio;
+ unsigned short ioprio_class, org_ioprio_class;
+
+ pid_t pid;
+};
+
+/*
* Per block device queue structure
*/
struct cfq_data {
@@ -135,51 +180,11 @@ struct cfq_data {
unsigned int cfq_slice_idle;

struct list_head cic_list;
-};

-/*
- * Per process-grouping structure
- */
-struct cfq_queue {
- /* reference count */
- atomic_t ref;
- /* various state flags, see below */
- unsigned int flags;
- /* parent cfq_data */
- struct cfq_data *cfqd;
- /* service_tree member */
- struct rb_node rb_node;
- /* service_tree key */
- unsigned long rb_key;
- /* prio tree member */
- struct rb_node p_node;
- /* prio tree root we belong to, if any */
- struct rb_root *p_root;
- /* sorted list of pending requests */
- struct rb_root sort_list;
- /* if fifo isn't expired, next request to serve */
- struct request *next_rq;
- /* requests queued in sort_list */
- int queued[2];
- /* currently allocated requests */
- int allocated[2];
- /* fifo list of requests in sort_list */
- struct list_head fifo;
-
- unsigned long slice_end;
- long slice_resid;
- unsigned int slice_dispatch;
-
- /* pending metadata requests */
- int meta_pending;
- /* number of requests that are on the dispatch list or inside driver */
- int dispatched;
-
- /* io prio of this group */
- unsigned short ioprio, org_ioprio;
- unsigned short ioprio_class, org_ioprio_class;
-
- pid_t pid;
+ /*
+ * Fallback dummy cfqq for extreme OOM conditions
+ */
+ struct cfq_queue oom_cfqq;
};

enum cfqq_state_flags {
@@ -1686,28 +1691,28 @@ retry:
*/
spin_unlock_irq(cfqd->queue->queue_lock);
new_cfqq = kmem_cache_alloc_node(cfq_pool,
- gfp_mask | __GFP_NOFAIL | __GFP_ZERO,
+ gfp_mask | __GFP_ZERO,
cfqd->queue->node);
spin_lock_irq(cfqd->queue->queue_lock);
- goto retry;
+ if (new_cfqq)
+ goto retry;
} else {
cfqq = kmem_cache_alloc_node(cfq_pool,
gfp_mask | __GFP_ZERO,
cfqd->queue->node);
- if (!cfqq)
- goto out;
}

- cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
- cfq_init_prio_data(cfqq, ioc);
- cfq_log_cfqq(cfqd, cfqq, "alloced");
+ if (cfqq) {
+ cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
+ cfq_init_prio_data(cfqq, ioc);
+ cfq_log_cfqq(cfqd, cfqq, "alloced");
+ } else
+ cfqq = &cfqd->oom_cfqq;
}

if (new_cfqq)
kmem_cache_free(cfq_pool, new_cfqq);

-out:
- WARN_ON((gfp_mask & __GFP_WAIT) && !cfqq);
return cfqq;
}

@@ -1740,11 +1745,8 @@ cfq_get_queue(struct cfq_data *cfqd, int is_sync, struct io_context *ioc,
cfqq = *async_cfqq;
}

- if (!cfqq) {
+ if (!cfqq)
cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);
- if (!cfqq)
- return NULL;
- }

/*
* pin the queue now that it's allocated, scheduler exit will prune it
@@ -2470,6 +2472,14 @@ static void *cfq_init_queue(struct request_queue *q)
for (i = 0; i < CFQ_PRIO_LISTS; i++)
cfqd->prio_trees[i] = RB_ROOT;

+ /*
+ * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
+ * Grab a permanent reference to it, so that the normal code flow
+ * will not attempt to free it.
+ */
+ cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
+ atomic_inc(&cfqd->oom_cfqq.ref);
+
INIT_LIST_HEAD(&cfqd->cic_list);

cfqd->queue = q;
--
1.6.3.2.306.g4f4fa