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c99d0c5801
refcount(9) was recently extended to support waiting on a refcount to drop to zero, as this was needed for a lockless VM object paging-in-progress counter. However, this adds overhead to all uses of refcount(9) and doesn't really match traditional refcounting semantics: once a counter has dropped to zero, the protected object may be freed at any point and it is not safe to dereference the counter. This change removes that extension and instead adds a new set of KPIs, blockcount_*, for use by VM object PIP and busy. Reviewed by: jeff, kib, mjg Tested by: pho Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D23723
52 lines
2 KiB
C
52 lines
2 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 2020 The FreeBSD Foundation
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*
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* This software was developed by Mark Johnston under sponsorship from
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* the FreeBSD Foundation.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef __SYS__BLOCKCOUNT_H__
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#define __SYS__BLOCKCOUNT_H__
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#include <machine/atomic.h>
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typedef struct _blockcount {
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unsigned int __count;
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} blockcount_t;
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#define _BLOCKCOUNT_WAITERS_FLAG (1U << 31)
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#define _BLOCKCOUNT_COUNT(c) ((c) & ~_BLOCKCOUNT_WAITERS_FLAG)
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#define _BLOCKCOUNT_WAITERS(c) (((c) & _BLOCKCOUNT_WAITERS_FLAG) != 0)
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static inline unsigned int
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blockcount_read(blockcount_t *count)
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{
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return (_BLOCKCOUNT_COUNT(atomic_load_int(&count->__count)));
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}
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#endif /* !__SYS__BLOCKCOUNT_H__ */
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