Explain how to use pagefault readaround to decrease the disk spinup frequency.



---

 25-akpm/Documentation/laptop-mode.txt |   16 ++++++++++++++++
 1 files changed, 16 insertions(+)

diff -puN Documentation/laptop-mode.txt~laptop-mode-readahead Documentation/laptop-mode.txt
--- 25/Documentation/laptop-mode.txt~laptop-mode-readahead	2004-03-26 01:11:59.969132648 -0800
+++ 25-akpm/Documentation/laptop-mode.txt	2004-03-26 01:14:18.868016808 -0800
@@ -120,6 +120,18 @@ Tips & Tricks
   this on powerbooks too. I hope that this is a piece of information that
   might be useful to the Laptop Mode patch or it's users."
 
+* One thing which will cause disks to spin up is not-present application
+  and dynamic library text pages.  The kernel will load program text off disk
+  on-demand, so each time you invoke an application feature for the first
+  time, the kernel needs to spin the disk up to go and fetch that part of the
+  application.
+
+  So it is useful to increase the disk readahead parameter greatly, so that
+  the kernel will pull all of the executable's pages into memory on the first
+  pagefault.
+
+  The supplied script does this.
+
 
 Control script
 --------------
@@ -180,6 +192,8 @@ DIRTY_RATIO=40
 #
 DIRTY_BACKGROUND_RATIO=5
 
+READAHEAD=4096		# kilobytes
+
 # kernel default dirty buffer age
 DEF_AGE=30
 DEF_UPDATE=5
@@ -222,6 +236,7 @@ case "$1" in
 					"reiserfs")	mount $DEV -t $FST $MP -o remount,$PARSEDOPTS,commit=$MAX_AGE,noatime ;;
 					"xfs")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS,commit=$MAX_AGE,noatime ;;
 				esac
+				blockdev --setra $((READAHEAD * 2)) $DEV
 			done
 		fi
 		echo "."
@@ -251,6 +266,7 @@ case "$1" in
 					"reiserfs")	mount $DEV -t $FST $MP -o remount,$PARSEDOPTS ;;
 					"xfs")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS ;;
 				esac
+				blockdev --setra 256 $DEV
 			done
 		fi
 		echo "."

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