From owner-freebsd-hackers  Tue Dec  5 12:35: 1 2000
From owner-freebsd-hackers@FreeBSD.ORG  Tue Dec  5 12:34:57 2000
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Date: Tue, 5 Dec 2000 12:34:56 -0800
From: Alfred Perlstein <bright@wintelcom.net>
To: peter@freebsd.org
Cc: dillon@freebsd.org, hackers@freebsd.org
Subject: phys backed shm patch.
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Ok, I spent quite some time trying to figure out why postgresql
would "hang" when using the 'kern.ipc.shm_use_phys' sysctl.

It finally came down to some spinlocks that were being corrupted
in a very tiny shared memory segment.

It seems like the phys_pager doesn't correctly allocate when
given a non PAGE_SIZE'd 'size' so then I think odd stuff happens
to the memory in the pages:

Index: phys_pager.c
===================================================================
RCS file: /home/ncvs/src/sys/vm/phys_pager.c,v
retrieving revision 1.3.2.1
diff -u -u -r1.3.2.1 phys_pager.c
--- phys_pager.c	2000/08/04 22:31:11	1.3.2.1
+++ phys_pager.c	2000/12/05 20:13:25
@@ -83,7 +83,7 @@
 		 * Allocate object and associate it with the pager.
 		 */
 		object = vm_object_allocate(OBJT_PHYS,
-			OFF_TO_IDX(foff + size));
+			OFF_TO_IDX(foff + PAGE_MASK + size));
 		object->handle = handle;
 		TAILQ_INSERT_TAIL(&phys_pager_object_list, object,
 		    pager_object_list);


I basically grabbed this from the swap_pager.c code and it seems
to work.

I'd like to commit it to both current and stable asap (afaik no
one uses kern.ipc.shm_use_phys anyhow, we missed the boat on
Oracle)

-- 
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
"I have the heart of a child; I keep it in a jar on my desk."


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