b64400a03f
document one of the optional flags; clarify which of the flags are optional (and which are not), and remove mention of a restriction on the reclamation of cached pages that no longer holds since version 7. MFC after: 1 week
137 lines
4.1 KiB
Groff
137 lines
4.1 KiB
Groff
.\"
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.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved.
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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
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" 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 SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 3, 2010
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.Dt VM_PAGE_ALLOC 9
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.Os
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.Sh NAME
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.Nm vm_page_alloc
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.Nd "allocate a page for a"
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.Vt vm_object
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.Sh SYNOPSIS
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.In sys/param.h
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.In vm/vm.h
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.In vm/vm_page.h
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.Ft vm_page_t
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.Fn vm_page_alloc "vm_object_t object" "vm_pindex_t pindex" "int req"
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.Sh DESCRIPTION
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The
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.Fn vm_page_alloc
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function allocates a page at
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.Fa pindex
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within
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.Fa object .
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It is assumed that a page has not already been allocated at
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.Fa pindex .
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The page returned is inserted into the object, unless
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.Dv VM_ALLOC_NOOBJ
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is specified in the
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.Fa req .
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The page may exist in the vm object cache, in which case it will
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be reactivated instead, moving from the cache into the object page list.
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.Pp
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.Fn vm_page_alloc
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will not sleep.
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.Pp
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Its arguments are:
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.Bl -tag -width ".Fa object"
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.It Fa object
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The VM object to allocate the page for.
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The
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.Fa object
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must be locked if
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.Dv VM_ALLOC_NOOBJ
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is not specified.
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.It Fa pindex
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The index into the object at which the page should be inserted.
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.It Fa req
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The bitwise-inclusive OR of a class and any optional flags indicating
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how the page should be allocated.
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.Pp
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Exactly one of the following classes must be specified:
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.Bl -tag -width ".Dv VM_ALLOC_INTERRUPT"
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.It Dv VM_ALLOC_NORMAL
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The page should be allocated with no special treatment.
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.It Dv VM_ALLOC_SYSTEM
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The page can be allocated if the cache is empty and the free
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page count is above the interrupt reserved water mark.
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This flag should be used only when the system really needs the page.
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.It Dv VM_ALLOC_INTERRUPT
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.Fn vm_page_alloc
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is being called during an interrupt.
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A page will be returned successfully if the free page count is greater
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than zero.
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.El
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.Pp
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The optional flags are:
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.Bl -tag -width ".Dv VM_ALLOC_IFNOTCACHED"
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.It Dv VM_ALLOC_ZERO
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Indicate a preference for a pre-zeroed page.
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There is no guarantee that the returned page will be zeroed, but it
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will have the
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.Dv PG_ZERO
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flag set if it is zeroed.
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.It Dv VM_ALLOC_NOOBJ
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Do not associate the allocated page with a vm object.
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The
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.Fa object
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argument is ignored.
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.It Dv VM_ALLOC_NOBUSY
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The returned page will not have the
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.Dv VPO_BUSY
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flag set.
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.It Dv VM_ALLOC_WIRED
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The returned page will be wired.
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.It Dv VM_ALLOC_IFCACHED
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Allocate the page only if it is cached.
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Otherwise, return
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.Dv NULL .
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.It Dv VM_ALLOC_IFNOTCACHED
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Only allocate the page if it is not cached in the
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.Fa object .
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If the page at the specified
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.Fa pindex
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is cached, NULL is returned instead.
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.El
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.El
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.Sh RETURN VALUES
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The
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.Vt vm_page_t
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that was allocated is returned if successful; otherwise,
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.Dv NULL
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is returned.
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.Sh NOTES
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The pager process is always upgraded to
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.Dv VM_ALLOC_SYSTEM
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unless
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.Dv VM_ALLOC_INTERRUPT
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is set.
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.Sh AUTHORS
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This manual page was written by
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.An Chad David Aq davidc@acns.ab.ca .
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