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(re)Introduce locking for amaps & anons.

A rwlock is attached to every amap and is shared with all its anon.  The
same lock will be used by multiple amaps if they have anons in common.

This should be enough to get the upper part of the fault handler out of the
KERNEL_LOCK() which seems to bring up to 20% improvements in builds.

This is based/copied/adapted from the most recent work done in NetBSD which
is an evolution of the precendent simple_lock scheme.

Tested by many, thanks!

ok kettenis@, mvs@

/*	$OpenBSD: uvm_anon.h,v 1.22 2021/01/19 13:21:36 mpi Exp $	*/
/*	$NetBSD: uvm_anon.h,v 1.13 2000/12/27 09:17:04 chs Exp $	*/

/*
 * Copyright (c) 1997 Charles D. Cranor and Washington University.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef _UVM_UVM_ANON_H_
#define _UVM_UVM_ANON_H_

/*
 * anonymous memory management
 *
 * anonymous virtual memory is short term virtual memory that goes away
 * when the processes referencing it go away.    an anonymous page of
 * virtual memory is described by the following data structure:
 */

struct vm_anon {
	struct rwlock *an_lock;

	struct vm_page *an_page;	/* if in RAM */
	int an_ref;			/* reference count */

	/*
	 * Drum swap slot # (if != 0) [if we hold an_page, PG_BUSY]
	 */
	int an_swslot;
};

/*
 * for active vm_anon's the data can be in one of the following state:
 * [1] in a vm_page with no backing store allocated yet, [2] in a vm_page
 * with backing store allocated, or [3] paged out to backing store
 * (no vm_page).
 *
 * for pageout in case [2]: if the page has been modified then we must
 * flush it out to backing store, otherwise we can just dump the
 * vm_page.
 */

/*
 * anons are grouped together in anonymous memory maps, or amaps.
 * amaps are defined in uvm_amap.h.
 */

/*
 * processes reference anonymous virtual memory maps with an anonymous 
 * reference structure:
 * Note that the offset field indicates which part of the amap we are
 * referencing.
 * Locked by vm_map lock.
 */

struct vm_aref {
	int ar_pageoff;			/* page offset into amap we start */
	struct vm_amap *ar_amap;	/* pointer to amap */
};

#ifdef _KERNEL
struct vm_anon	*uvm_analloc(void);
void		 uvm_anfree_list(struct vm_anon *, struct pglist *);
void		 uvm_anon_release(struct vm_anon *);
void		 uvm_anwait(void);
void		 uvm_anon_init(void);
void		 uvm_anon_dropswap(struct vm_anon *);
boolean_t	 uvm_anon_pagein(struct vm_amap *, struct vm_anon *);

#define		uvm_anfree(an)	uvm_anfree_list((an), NULL)

#endif /* _KERNEL */

#endif /* _UVM_UVM_ANON_H_ */