Re: 2.3.47: elevator nr_segments x should be x+1

From: Andrea Arcangeli (andrea@suse.de)
Date: Sat Mar 04 2000 - 14:11:02 EST


On Tue, 22 Feb 2000, Andrea Arcangeli wrote:

>On 21 Feb 2000, David Wragg wrote:
>
>>The bad news is this:
>>
>>03:08: elevator nr_segments 197 should be 198
>>03:08: elevator nr_segments 239 should be 240
>
>Don't worry about this. It's can't harm per se. Anyway it's interesting to
>discover why this is happening. Can you reproduce?

This patch against 2.3.49 will fix the above warning:

--- elevator/drivers/block/DAC960.c.~1~ Fri Mar 3 02:19:23 2000
+++ elevator/drivers/block/DAC960.c Sat Mar 4 19:53:03 2000
@@ -1051,20 +1051,23 @@
         int max_segments;
         DAC960_Controller_T * Controller = q->queuedata;
         int total_segments = req->nr_segments + next->nr_segments;
+ int same_segment;
 
         max_segments = Controller->MaxSegmentsPerRequest[MINOR(req->rq_dev)];
         if (__max_segments < max_segments)
                 max_segments = __max_segments;
 
+ same_segment = 0;
         if (req->bhtail->b_data + req->bhtail->b_size == next->bh->b_data)
         {
                 total_segments--;
- q->nr_segments--;
+ same_segment = 1;
         }
     
         if (total_segments > max_segments)
                 return 0;
 
+ q->nr_segments -= same_segment;
         req->nr_segments = total_segments;
         return 1;
 }
--- elevator/drivers/block/ll_rw_blk.c.~1~ Sun Feb 27 06:19:42 2000
+++ elevator/drivers/block/ll_rw_blk.c Sat Mar 4 19:53:58 2000
@@ -212,15 +212,18 @@
                                 struct request *next, int max_segments)
 {
         int total_segments = req->nr_segments + next->nr_segments;
+ int same_segment;
 
+ same_segment = 0;
         if (req->bhtail->b_data + req->bhtail->b_size == next->bh->b_data) {
                 total_segments--;
- q->nr_segments--;
+ same_segment = 1;
         }
     
         if (total_segments > max_segments)
                 return 0;
 
+ q->nr_segments -= same_segment;
         req->nr_segments = total_segments;
         return 1;
 }

You can test it while I fix the other minor glitches.

Andrea

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