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Although we perform path compression to reduce the height of the trie and

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the number of interior nodes, we always create a level zero interior node at
the root of every non-empty trie, even when that node is not strictly
necessary, i.e., it has only one child.  This change is the first step in
eliminating those unnecessary level zero interior nodes.  Specifically, it
updates all of the lookup functions so that they do not require a level zero
interior node at the root.

Reviewed by:	attilio, jeff (an earlier version)
Sponsored by:	EMC / Isilon Storage Division
This commit is contained in:
Alan Cox 2013-04-12 20:21:28 +00:00
parent d184218c18
commit 6f9c0b15bb
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=249427
1 changed files with 33 additions and 20 deletions
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49
sys/vm/vm_radix.c
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@ -270,10 +270,6 @@ vm_radix_addlev(vm_pindex_t *idx, boolean_t *levels, uint16_t ilev)
for (; levels[ilev] == FALSE ||
vm_radix_slot(*idx, ilev) == (VM_RADIX_COUNT - 1); ilev--)
if (ilev == 0)
break;
KASSERT(ilev > 0 || levels[0],
("%s: levels back-scanning problem", __func__));
if (ilev == 0 && vm_radix_slot(*idx, ilev) == (VM_RADIX_COUNT - 1))
return (1);
wrapidx = *idx;
*idx = vm_radix_trimkey(*idx, ilev);
@ -295,10 +291,6 @@ vm_radix_declev(vm_pindex_t *idx, boolean_t *levels, uint16_t ilev)
for (; levels[ilev] == FALSE ||
vm_radix_slot(*idx, ilev) == 0; ilev--)
if (ilev == 0)
break;
KASSERT(ilev > 0 || levels[0],
("%s: levels back-scanning problem", __func__));
if (ilev == 0 && vm_radix_slot(*idx, ilev) == 0)
return (1);
wrapidx = *idx;
*idx = vm_radix_trimkey(*idx, ilev);
@ -474,17 +466,16 @@ vm_radix_lookup(struct vm_radix *rtree, vm_pindex_t index)
rnode = vm_radix_getroot(rtree);
while (rnode != NULL) {
if (vm_radix_keybarr(rnode, index))
return (NULL);
slot = vm_radix_slot(index, rnode->rn_clev);
rnode = rnode->rn_child[slot];
if (vm_radix_isleaf(rnode)) {
m = vm_radix_topage(rnode);
if (m->pindex == index)
return (m);
else
return (NULL);
}
break;
} else if (vm_radix_keybarr(rnode, index))
break;
slot = vm_radix_slot(index, rnode->rn_clev);
rnode = rnode->rn_child[slot];
}
return (NULL);
}
@ -505,12 +496,21 @@ vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index)
int loops = 0;
#endif
rnode = vm_radix_getroot(rtree);
if (rnode == NULL)
return (NULL);
else if (vm_radix_isleaf(rnode)) {
m = vm_radix_topage(rnode);
if (m->pindex >= index)
return (m);
else
return (NULL);
}
restart:
KASSERT(++loops < 1000, ("%s: too many loops", __func__));
for (difflev = 0; difflev < (VM_RADIX_LIMIT + 1); difflev++)
maplevels[difflev] = FALSE;
rnode = vm_radix_getroot(rtree);
while (rnode != NULL) {
for (;;) {
maplevels[rnode->rn_clev] = TRUE;
/*
@ -532,6 +532,7 @@ vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index)
} else
index = vm_radix_trimkey(rnode->rn_owner,
difflev);
rnode = vm_radix_getroot(rtree);
goto restart;
}
slot = vm_radix_slot(index, rnode->rn_clev);
@ -572,6 +573,7 @@ vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index)
if (rnode->rn_clev == 0 || vm_radix_addlev(&index, maplevels,
rnode->rn_clev - 1) > 0)
break;
rnode = vm_radix_getroot(rtree);
goto restart;
descend:
rnode = child;
@ -595,12 +597,21 @@ vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index)
int loops = 0;
#endif
rnode = vm_radix_getroot(rtree);
if (rnode == NULL)
return (NULL);
else if (vm_radix_isleaf(rnode)) {
m = vm_radix_topage(rnode);
if (m->pindex <= index)
return (m);
else
return (NULL);
}
restart:
KASSERT(++loops < 1000, ("%s: too many loops", __func__));
for (difflev = 0; difflev < (VM_RADIX_LIMIT + 1); difflev++)
maplevels[difflev] = FALSE;
rnode = vm_radix_getroot(rtree);
while (rnode != NULL) {
for (;;) {
maplevels[rnode->rn_clev] = TRUE;
/*
@ -622,6 +633,7 @@ vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index)
} else if (vm_radix_declev(&index, maplevels,
difflev) > 0)
break;
rnode = vm_radix_getroot(rtree);
goto restart;
}
slot = vm_radix_slot(index, rnode->rn_clev);
@ -663,6 +675,7 @@ vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index)
if (rnode->rn_clev == 0 || vm_radix_declev(&index, maplevels,
rnode->rn_clev - 1) > 0)
break;
rnode = vm_radix_getroot(rtree);
goto restart;
descend:
rnode = child;