On Oct 26, 2001 08:39 -0500, Robert Macaulay wrote:
> Where is the patch you referred to to increase the read ahead? Part of our
> Oracle testing(with volumes separated by use) involves sequential table
> scans, which sound like they could benefit greatly from this patch. Thx
I'm not sure of the exact time when the changes went in, but when I
updated to 2.4.13 and wanted to update the LVM code also, I see (note
patch whitespace may be broken because of cut-n-paste):
There was also a small discussion about read ahead on the kernel mailing
list, so this may be a result of that. Something along the lines of "all
readahead is broken because ..."
Cheers, Andreas
=============================================================================
--- kernel/lvm.c 2001/10/15 09:23:27
+++ kernel/lvm.c 2001/10/26 17:21:47
@@ -270,9 +270,13 @@
#include "lvm-internal.h"
-#define LVM_CORRECT_READ_AHEAD( a) \
- if ( a < LVM_MIN_READ_AHEAD || \
- a > LVM_MAX_READ_AHEAD) a = LVM_MAX_READ_AHEAD;
+#define LVM_CORRECT_READ_AHEAD(a) \
+do { \
+ if ((a) < LVM_MIN_READ_AHEAD || \
+ (a) > LVM_MAX_READ_AHEAD) \
+ (a) = LVM_DEFAULT_READ_AHEAD; \
+ read_ahead[MAJOR_NR] = (a); \
+} while(0)
#ifndef WRITEA
# define WRITEA WRITE
@@ -1040,6 +1045,7 @@
(long) arg > LVM_MAX_READ_AHEAD)
return -EINVAL;
lv_ptr->lv_read_ahead = (long) arg;
+ read_ahead[MAJOR_NR] = lv_ptr->lv_read_ahead;
break;
--- kernel/lvm.h 2001/10/03 14:46:47 1.34
+++ kernel/lvm.h 2001/10/26 17:24:16
@@ -274,8 +274,9 @@
#define LVM_MAX_STRIPES 128 /* max # of stripes */
#define LVM_MAX_SIZE ( 1024LU * 1024 / SECTOR_SIZE * 1024 *
1024) /* 1TB[sectors] */
#define LVM_MAX_MIRRORS 2 /* future use */
-#define LVM_MIN_READ_AHEAD 2 /* minimum read ahead sectors */
-#define LVM_MAX_READ_AHEAD 120 /* maximum read ahead sectors */
+#define LVM_MIN_READ_AHEAD 0 /* minimum read ahead sectors */
+#define LVM_DEFAULT_READ_AHEAD 1024 /* sectors for 512k scsi segments */
+#define LVM_MAX_READ_AHEAD 10000 /* maximum read ahead sectors */
#define LVM_MAX_LV_IO_TIMEOUT 60 /* seconds I/O timeout (future use) */
#define LVM_PARTITION 0xfe /* LVM partition id */
#define LVM_NEW_PARTITION 0x8e /* new LVM partition id (10/09/1999) */
Cheers, Andreas
--
Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
\ would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert
