Hi,
The cciss driver set a too high default value for the number of read ahead
pages. When a lot of read operation happens, then we enter into a
trash-like vm situation.
Below is what happens into such a situation:
The system is a HP Proliant 385, with a Debian sarge amd64 distribution.
It collect snmp values and stored into RRD files and therefore
perform a lot of small read and write operations.
# cat /sys/block/cciss\!c0d0/queue/read_ahead_kb
4096
# dstat 1
----total-cpu-usage---- -disk/total -net/total- ---paging-- ---system--
usr sys idl wai hiq siq|_read write|_recv _send|__in_ _out_|_int_ _csw_
0 0 97 2 0 0| 0 0 | 0 0 | 0 0 | 0 0
0 2 50 47 0 0|75.1M 4096B|1226B 4056B| 0 0 |1005 451
0 1 48 50 0 0|32.6M 1766k| 70B 326B| 0 0 | 951 373
0 2 49 49 0 0|57.8M 20k| 70B 326B| 0 0 | 873 487
0 2 50 48 0 0|56.7M 24k| 184B 440B| 0 0 | 882 537
0 2 48 50 0 0|55.1M 64k| 70B 326B| 0 0 | 877 532
0 2 50 48 0 0|53.6M 20k| 70B 326B| 0 0 | 860 521
0 0 50 50 0 0|31.1M 1464k| 70B 326B| 0 0 | 892 457
18 3 31 48 0 0|45.7M 64k| 70B 326B| 0 0 |1075 594
...
# echo 128 > /sys/block/cciss\!c0d0/queue/read_ahead_kb
(wait 5 to 10 minutes)
# dstat 1
----total-cpu-usage---- -disk/total -net/total- ---paging-- ---system--
usr sys idl wai hiq siq|_read write|_recv _send|__in_ _out_|_int_ _csw_
0 0 97 2 0 0| 0 0 | 0 0 | 0 0 | 0 0
0 0 100 0 0 0| 0 12k| 140B 1004B| 0 0 | 258 16
0 0 100 0 0 0| 0 3072B| 204B 716B| 0 0 | 257 28
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 10
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 14
0 0 99 1 0 0| 0 1948k| 140B 652B| 0 0 | 742 86
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 14
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 30
2 1 98 0 0 0| 0 0 | 140B 652B| 0 0 | 255 30
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 10
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 25
14 0 86 0 0 0| 0 0 | 254B 766B| 0 0 | 436 49
12 12 77 0 0 0| 0 165k|32.4k 33.4k| 0 0 | 339 1773
10 6 84 1 0 0| 196k 0 | 140B 652B| 0 0 | 262 31
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 14
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 255 13
2 1 97 0 0 0| 0 20k| 576B 1898B| 0 0 | 269 40
0 0 100 0 0 0| 0 140k| 140B 652B| 0 0 | 264 39
0 0 100 0 0 0| 0 0 | 140B 652B| 0 0 | 257 17
10 4 86 0 0 0| 0 0 | 204B 716B| 0 0 | 255 25
I think we should in fact totally kill the whole ra_pages stuff under the
cciss driver IMHO.
Signed-off-by: Bruno Ducrot <[email protected]>
linux-2.6.16/drivers/block/cciss.c | 3 ---
1 files changed, 3 deletions(-)
--- linux-2.6.16/drivers/block/cciss.c 2006/03/22 12:06:30 1.1
+++ linux-2.6.16/drivers/block/cciss.c 2006/03/23 08:29:57
@@ -137,7 +137,6 @@ static struct board_type products[] = {
/*define how many times we will try a command because of bus resets */
#define MAX_CMD_RETRIES 3
-#define READ_AHEAD 1024
#define NR_CMDS 384 /* #commands that can be outstanding */
#define MAX_CTLR 32
@@ -1238,7 +1237,6 @@ static void cciss_update_drive_info(int
disk->queue = blk_init_queue(do_cciss_request, &h->lock);
/* Set up queue information */
- disk->queue->backing_dev_info.ra_pages = READ_AHEAD;
blk_queue_bounce_limit(disk->queue, hba[ctlr]->pdev->dma_mask);
/* This is a hardware imposed limit. */
@@ -3217,7 +3215,6 @@ static int __devinit cciss_init_one(stru
}
drv->queue = q;
- q->backing_dev_info.ra_pages = READ_AHEAD;
blk_queue_bounce_limit(q, hba[i]->pdev->dma_mask);
/* This is a hardware imposed limit. */
--
Bruno Ducrot
-- Which is worse: ignorance or apathy?
-- Don't know. Don't care.
-
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