[PATCH] dynamic request allocation

This patch adds dynamic allocation of request structures. Right now we
are reserving 256 requests per initialized queue, which adds up to quite
a lot of memory for even a modest number of queues. For the quoted 4000
disk systems, it's a disaster.

Instead, we mempool 4 requests per queue and put an upper limit on the
number of requests that we will put in-flight as well. I've kept the 128
read/write max in-flight limit for now. It is trivial to experiement
with larger queue sizes now, but I want to change one thing at the time
(the truncate scenario doesn't look all that good with a huge number of
requests, for instance).

Patch has been in -mm for a while, I'm running it here against stock 2.5
as well. Additionally, it actually kills quite a bit of code as well

2 files changed, 14 insertions, 5 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 32a8cddd2ca3..4c53e7bbcc25 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -10,6 +10,7 @@
 #include <linux/pagemap.h>
 #include <linux/backing-dev.h>
 #include <linux/wait.h>
+#include <linux/mempool.h>
 
 #include <asm/scatterlist.h>
 
@@ -18,10 +19,12 @@ typedef struct request_queue request_queue_t;
 struct elevator_s;
 typedef struct elevator_s elevator_t;
 
+#define BLKDEV_MIN_RQ	4
+#define BLKDEV_MAX_RQ	128
+
 struct request_list {
-	unsigned int count;
-	struct list_head free;
-	wait_queue_head_t wait;
+	int count[2];
+	mempool_t *rq_pool;
 };
 
 /*
@@ -180,7 +183,7 @@ struct request_queue
 	/*
 	 * the queue request freelist, one for reads and one for writes
 	 */
-	struct request_list	rq[2];
+	struct request_list	rq;
 
 	request_fn_proc		*request_fn;
 	merge_request_fn	*back_merge_fn;
@@ -329,7 +332,6 @@ extern void blk_put_request(struct request *);
 extern void blk_attempt_remerge(request_queue_t *, struct request *);
 extern void __blk_attempt_remerge(request_queue_t *, struct request *);
 extern struct request *blk_get_request(request_queue_t *, int, int);
-extern struct request *__blk_get_request(request_queue_t *, int);
 extern void blk_put_request(struct request *);
 extern void blk_insert_request(request_queue_t *, struct request *, int, void *);
 extern void blk_plug_device(request_queue_t *);
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 69648f495dc1..ef4e0e6c3ef7 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -15,6 +15,8 @@ typedef int (elevator_queue_empty_fn) (request_queue_t *);
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
 typedef struct request *(elevator_request_list_fn) (request_queue_t *, struct request *);
 typedef struct list_head *(elevator_get_sort_head_fn) (request_queue_t *, struct request *);
+typedef int (elevator_set_req_fn) (request_queue_t *, struct request *, int);
+typedef void (elevator_put_req_fn) (request_queue_t *, struct request *);
 
 typedef int (elevator_init_fn) (request_queue_t *, elevator_t *);
 typedef void (elevator_exit_fn) (request_queue_t *, elevator_t *);
@@ -34,6 +36,9 @@ struct elevator_s
 	elevator_request_list_fn *elevator_former_req_fn;
 	elevator_request_list_fn *elevator_latter_req_fn;
 
+	elevator_set_req_fn *elevator_set_req_fn;
+	elevator_put_req_fn *elevator_put_req_fn;
+
 	elevator_init_fn *elevator_init_fn;
 	elevator_exit_fn *elevator_exit_fn;
 
@@ -59,6 +64,8 @@ extern struct request *elv_former_request(request_queue_t *, struct request *);
 extern struct request *elv_latter_request(request_queue_t *, struct request *);
 extern int elv_register_queue(struct gendisk *);
 extern void elv_unregister_queue(struct gendisk *);
+extern int elv_set_request(request_queue_t *, struct request *, int);
+extern void elv_put_request(request_queue_t *, struct request *);
 
 #define __elv_add_request_pos(q, rq, pos)	\
 	(q)->elevator.elevator_add_req_fn((q), (rq), (pos))