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From: Ivan Voras <ivoras@FreeBSD.org>
Date: Mon, 9 Aug 2010 22:22:46 +0000 (UTC)
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Subject: svn commit: r211123 - head/sys/kern
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Author: ivoras
Date: Mon Aug  9 22:22:46 2010
New Revision: 211123
URL: http://svn.freebsd.org/changeset/base/211123

Log:
  Elaborate on how hirunningspace was chosen.

Modified:
  head/sys/kern/vfs_bio.c

Modified: head/sys/kern/vfs_bio.c
==============================================================================
--- head/sys/kern/vfs_bio.c	Mon Aug  9 22:22:06 2010	(r211122)
+++ head/sys/kern/vfs_bio.c	Mon Aug  9 22:22:46 2010	(r211123)
@@ -622,8 +622,11 @@ bufinit(void)
 
 	/*
 	 * Note: The 16 MB upper limit for hirunningspace was chosen
-	 * arbitrarily and may need further tuning. The lower 1 MB
-	 * limit is the historical upper limit for hirunningspace.
+	 * arbitrarily and may need further tuning. It corresponds to
+	 * 128 outstanding write IO requests (if IO size is 128 KiB),
+	 * which fits with many RAID controllers' tagged queing limits.
+	 * The lower 1 MB limit is the historical upper limit for
+	 * hirunningspace.
 	 */
 	hirunningspace = lmax(lmin(roundup(hibufspace / 64, MAXBSIZE),
 	    16 * 1024 * 1024), 1024 * 1024);