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Subject: [patch] remove magic numbers in block queue initialization
From: Robert Love <rml@tech9.net>
To: akpm@digeo.com
Cc: linux-kernel@vger.kernel.org
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Date: 19 Nov 2002 18:06:39 -0500
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Andrew,

Your less-requests patch signaled a way-too-many magic numbers alarm
(not the patches fault, of course, but it pointed it out).

Attached patch removes the minimum queue length, maximum queue length,
factor of queue length that is number of batch requests, and the maximum
number of batch request magic numbers and replaces them with defines and
some comments.

Look OK?

	Robert Love


Replace magic numbers in block queue init with sexy defines.
 
 drivers/block/ll_rw_blk.c |   32 ++++++++++++++++++++++++--------
 1 files changed, 24 insertions(+), 8 deletions(-)


diff -urN linux-2.5.48/drivers/block/ll_rw_blk.c linux/drivers/block/ll_rw_blk.c
--- linux-2.5.48/drivers/block/ll_rw_blk.c	2002-11-17 23:29:22.000000000 -0500
+++ linux/drivers/block/ll_rw_blk.c	2002-11-19 17:59:07.000000000 -0500
@@ -2109,6 +2109,22 @@
 	__blk_put_request(req->q, req);
 }
 
+/*
+ * The maximum and minimum free requests slots in the queue are
+ * dynamically calculated as a function of total memory.  Below is the
+ * upper and lower bound to those calculations.  We do not want the
+ * queue too large, as more memory than desired can be under writeback.
+ */
+#define MAX_QUEUE_REQUESTS	128
+#define MIN_QUEUE_REQUESTS	16
+
+/*
+ * Number of requests to batch together is calculated as the queue size
+ * over BATCH_QUEUE_FACTOR.  This number is capped at MAX_BATCH_REQUESTS
+ */
+#define BATCH_QUEUE_FACTOR	8
+#define MAX_BATCH_REQUESTS	8
+
 int __init blk_dev_init(void)
 {
 	int total_ram = nr_free_pages() << (PAGE_SHIFT - 10);
@@ -2125,14 +2141,14 @@
 	 * We use this many requests for reads, and this many for writes.
 	 */
 	queue_nr_requests = (total_ram >> 9) & ~7;
-	if (queue_nr_requests < 16)
-		queue_nr_requests = 16;
-	if (queue_nr_requests > 128)
-		queue_nr_requests = 128;
-
-	batch_requests = queue_nr_requests / 8;
-	if (batch_requests > 8)
-		batch_requests = 8;
+	if (queue_nr_requests < MIN_QUEUE_REQUESTS)
+		queue_nr_requests = MIN_QUEUE_REQUESTS;
+	if (queue_nr_requests > MAX_QUEUE_REQUESTS)
+		queue_nr_requests = MAX_QUEUE_REQUESTS;
+
+	batch_requests = queue_nr_requests / BATCH_QUEUE_FACTOR;
+	if (batch_requests > MAX_BATCH_REQUESTS)
+		batch_requests = MAX_BATCH_REQUESTS;
 
 	printk("block request queues:\n");
 	printk(" %d requests per read queue\n", queue_nr_requests);



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