kern/114654: [patch] make vm_page_max_wired tunnable at run time

[Eugene Grosbein]

>Number:         114654
>Category:       kern
>Synopsis:       [patch] make vm_page_max_wired tunnable at run time
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Tue Jul 17 11:50:02 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Eugene Grosbein
>Release:        FreeBSD 6.2-STABLE i386
>Organization:
Svyaz-Service JSC
>Environment:
System: FreeBSD grosbein.pp.ru 6.2-STABLE FreeBSD 6.2-STABLE #0: Tue Jul 17 19:23:09 KRAST 2007 eu at grosbein.pp.ru:/usr/obj/usr/local/src/sys/DADV i386

>Description:
	The kernel limits number of pages mlock()'ed by a process
	to one third of vm.stats.vm.v_free_count to prevent damage
	from broken processes. However, sometimes there is a need to allow
	a process to mlock() more than half of free pages pool,
	one example is /usr/ports/sysutils/memtest.
	Let's make vm_page_max_wired tunnable at run time.

>How-To-Repeat:
	I've installed second 1Gb memory module to my system and
	want to quick-check (most part of) it. I've raised kern.maxdsize
	but the kernel still does not allow memtest to mlock() so many pages.

	Yes, I know the best method is to boot the system from floppy
	of CD with special memory tester. But I'd glad to see this
	way allowed too.
>Fix:

	Running kernel with the following patch, I may increase
	sysctl vm.max_wired value upto, say, 1.5Gb
	for the system having 2Gb RAM and still run memtest from X.org's
	xterm session (top shows "1802M Free" here).

--- sys/vm/vm_pageout.c.orig	Tue Jul 17 19:18:56 2007
+++ sys/vm/vm_pageout.c	Tue Jul 17 19:33:52 2007
@@ -203,6 +203,8 @@
 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
 
 int vm_page_max_wired;		/* XXX max # of wired pages system-wide */
+SYSCTL_INT(_vm, OID_AUTO, max_wired,
+	CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
 
 #if !defined(NO_SWAPPING)
 static void vm_pageout_map_deactivate_pages(vm_map_t, long);


Eugene Grosbein
>Release-Note:
>Audit-Trail:
>Unformatted: