d/freebsd-nq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Improve the comment and man page for vm_page_alloc(). Specifically,

Browse Source 
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
This commit is contained in:
Alan Cox 2010-07-03 18:25:37 +00:00
parent ed92e5c424
commit b64400a03f
2 changed files with 35 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
share/man/man9/vm_page_alloc.9
View File

@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd February 27, 2010
.Dd July 3, 2010
.Dt VM_PAGE_ALLOC 9
.Os
.Sh NAME
@ -38,7 +38,7 @@
.In vm/vm.h
.In vm/vm_page.h
.Ft vm_page_t
.Fn vm_page_alloc "vm_object_t object" "vm_pindex_t pindex" "int page_req"
.Fn vm_page_alloc "vm_object_t object" "vm_pindex_t pindex" "int req"
.Sh DESCRIPTION
The
.Fn vm_page_alloc
@ -51,16 +51,15 @@ It is assumed that a page has not already been allocated at
The page returned is inserted into the object, unless
.Dv VM_ALLOC_NOOBJ
is specified in the
.Fa page_req ,
but is not inserted into a pmap.
The page may exists in the vm object cache, in which case it will
.Fa req .
The page may exist in the vm object cache, in which case it will
be reactivated instead, moving from the cache into the object page list.
.Pp
.Fn vm_page_alloc
will not sleep.
.Pp
Its arguments are:
.Bl -tag -width ".Fa page_req"
.Bl -tag -width ".Fa object"
.It Fa object
The VM object to allocate the page for.
The
@ -70,40 +69,48 @@ must be locked if
is not specified.
.It Fa pindex
The index into the object at which the page should be inserted.
.It Fa page_req
A flag indicating how the page should be allocated.
.It Fa req
The bitwise-inclusive OR of a class and any optional flags indicating
how the page should be allocated.
.Pp
Exactly one of the following classes must be specified:
.Bl -tag -width ".Dv VM_ALLOC_INTERRUPT"
.It Dv VM_ALLOC_NORMAL
The page should be allocated with no special treatment.
.It Dv VM_ALLOC_SYSTEM
The page can be allocated if the cache queue is empty and the free
The page can be allocated if the cache is empty and the free
page count is above the interrupt reserved water mark.
If
.Dv VM_ALLOC_INTERRUPT
is set, the page can be allocated as long as the free page count is
greater than zero.
This flag should be used only when the system really needs the page.
.It Dv VM_ALLOC_INTERRUPT
.Fn vm_page_alloc
is being called during an interrupt and therefore the cache cannot
be accessed.
The page will only be returned successfully if the free count is greater
is being called during an interrupt.
A page will be returned successfully if the free page count is greater
than zero.
.El
.Pp
The optional flags are:
.Bl -tag -width ".Dv VM_ALLOC_IFNOTCACHED"
.It Dv VM_ALLOC_ZERO
Indicate a preference for a pre-zeroed page.
There is no guarantee that the page thus returned will be zeroed, but
it will be marked by
There is no guarantee that the returned page will be zeroed, but it
will have the
.Dv PG_ZERO
flag if it is zeroed.
flag set if it is zeroed.
.It Dv VM_ALLOC_NOOBJ
Do not associate the allocated page with a vm object.
The
.Fa object
argument is ignored.
.It Dv VM_ALLOC_NOBUSY
The page returned will not be busied.
The returned page will not have the
.Dv VPO_BUSY
flag set.
.It Dv VM_ALLOC_WIRED
The returned page is wired.
The returned page will be wired.
.It Dv VM_ALLOC_IFCACHED
Allocate the page only if it is cached.
Otherwise, return
.Dv NULL .
.It Dv VM_ALLOC_IFNOTCACHED
Only allocate the page if it is not cached in the
.Fa object .

9
sys/vm/vm_page.c
View File

@ -1144,14 +1144,19 @@ vm_page_cache_transfer(vm_object_t orig_object, vm_pindex_t offidxstart,
* Allocate and return a memory cell associated
* with this VM object/offset pair.
*
* page_req classes:
* The caller must always specify an allocation class.
*
* allocation classes:
* VM_ALLOC_NORMAL normal process request
* VM_ALLOC_SYSTEM system *really* needs a page
* VM_ALLOC_INTERRUPT interrupt time request
* VM_ALLOC_ZERO zero page
*
* optional allocation flags:
* VM_ALLOC_ZERO prefer a zeroed page
* VM_ALLOC_WIRED wire the allocated page
* VM_ALLOC_NOOBJ page is not associated with a vm object
* VM_ALLOC_NOBUSY do not set the page busy
* VM_ALLOC_IFCACHED return page only if it is cached
* VM_ALLOC_IFNOTCACHED return NULL, do not reactivate if the page
* is cached
*