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Markup fixes.

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This commit is contained in:
Ruslan Ermilov 2005-01-14 17:22:51 +00:00
parent 444acc1655
commit c7d01a0a6f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=140251
1 changed files with 22 additions and 11 deletions
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33
share/man/man9/vm_map_entry_resize_free.9
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@ -30,15 +30,13 @@
.Dt VM_MAP_ENTRY_RESIZE_FREE 9
.Sh NAME
.Nm vm_map_entry_resize_free
.Nd vm map free space algorithm
.Nd "vm map free space algorithm"
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/vm_map.h
.Ft void
.Fo vm_map_entry_resize_free
.Fa "vm_map_t map" "vm_map_entry_t entry"
.Fc
.Fn vm_map_entry_resize_free "vm_map_t map" "vm_map_entry_t entry"
.Sh DESCRIPTION
This manual page describes the
.Vt vm_map_entry
@ -58,7 +56,7 @@ and
pointers).
The search tree is organized as a Sleator and Tarjan splay tree,
also known as a
.Dq self-adjusting tree.
.Dq "self-adjusting tree" .
.Bd -literal -offset indent
struct vm_map_entry {
struct vm_map_entry *prev;
@ -75,11 +73,13 @@ struct vm_map_entry {
.Ed
.Pp
The free space algorithm adds two fields to
.Vt struct vm_map_entry :
.Vt "struct vm_map_entry" :
.Va adj_free
and
.Va max_free .
The
.Va adj_free
field
is the amount of free address space adjacent to and immediately
following (higher address) the map entry.
This field is unused in the map header.
@ -93,7 +93,9 @@ entry->adj_free = (entry->next == &map->header ?
map->max_offset : entry->next->start) - entry->end;
.Ed
.Pp
The
.Va max_free
field
is the maximum amount of contiguous free space in the entry's subtree.
Note that
.Va max_free
@ -108,14 +110,18 @@ Again,
.Va max_free
is unused in the map header.
.Pp
These fields allow for an O(log\~n) implementation of
These fields allow for an
.Fn O "log n"
implementation of
.Fn vm_map_findspace .
Using
.Va max_free ,
we can immediately test for a sufficiently large free region
in an entire subtree.
This makes it possible to find a first-fit free region of a given size
in one pass down the tree, so O(log\~n) amortized using splay trees.
in one pass down the tree, so
.Fn O "log n"
amortized using splay trees.
.Pp
When a free region changes size, we must update
.Va adj_free
@ -172,8 +178,9 @@ ret = vm_map_insert(map, object, offset, start, end, prot,
.Pp
In this case, no further action is required to maintain
consistency of the free space variables.
The
.Fn vm_map_insert
calls
function calls
.Fn vm_map_entry_link
which updates both the new entry and the previous entry.
The same would be true for
@ -225,8 +232,12 @@ on the entry itself.
.%D July 1985
.Re
.Sh HISTORY
Splay trees were added to the VM map in FreeBSD 5.0, and the
O(log\~n) tree-based free space algorithm was added in FreeBSD 5.3.
Splay trees were added to the VM map in
.Fx 5.0 ,
and the
.Fn O "log n"
tree-based free space algorithm was added in
.Fx 5.3 .
.Sh AUTHORS
The tree-based free space algorithm and this manual page were written by
.An Mark W. Krentel