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Avoid unnecessary page lookups in vm_object_madvise().

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vm_object_madvise() is frequently used to apply advice to a contiguous
set of pages in an object with no backing object. Optimize this case by
skipping non-resident subranges in constant time, and by iterating over
resident pages using the object memq, thus avoiding radix tree lookups on
each page index in the specified range.

While here, move MADV_WILLNEED handling to vm_page_advise(), and rename the
"advise" parameter to vm_object_madvise() to "advice."

Reviewed by:	alc, kib
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D9098
This commit is contained in:
Mark Johnston 2017-01-15 03:50:08 +00:00
parent 4ecb427a49
commit c2655a40a7
2 changed files with 39 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
sys/vm/vm_object.c
View File

@ -1097,7 +1097,7 @@ vm_object_sync(vm_object_t object, vm_ooffset_t offset, vm_size_t size,
*/
void
vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
int advise)
int advice)
{
vm_pindex_t tpindex;
vm_object_t backing_object, tobject;
@ -1105,11 +1105,9 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
if (object == NULL)
return;
VM_OBJECT_WLOCK(object);
/*
* Locate and adjust resident pages
*/
for (; pindex < end; pindex += 1) {
for (m = NULL; pindex < end; pindex++) {
relookup:
tobject = object;
tpindex = pindex;
@ -1118,7 +1116,7 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
* MADV_FREE only operates on OBJT_DEFAULT or OBJT_SWAP pages
* and those pages must be OBJ_ONEMAPPING.
*/
if (advise == MADV_FREE) {
if (advice == MADV_FREE) {
if ((tobject->type != OBJT_DEFAULT &&
tobject->type != OBJT_SWAP) ||
(tobject->flags & OBJ_ONEMAPPING) == 0) {
@ -1126,15 +1124,29 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
}
} else if ((tobject->flags & OBJ_UNMANAGED) != 0)
goto unlock_tobject;
m = vm_page_lookup(tobject, tpindex);
if (m == NULL) {
/*
* There may be swap even if there is no backing page
*/
if (advise == MADV_FREE && tobject->type == OBJT_SWAP)
/*
* In the common case where the object has no backing object, we
* can avoid performing lookups at each pindex. In either case,
* when applying MADV_FREE we take care to release any swap
* space used to store non-resident pages.
*/
if (object->backing_object == NULL) {
m = (m != NULL) ? TAILQ_NEXT(m, listq) :
vm_page_find_least(object, pindex);
tpindex = (m != NULL && m->pindex < end) ?
m->pindex : end;
if (advice == MADV_FREE && object->type == OBJT_SWAP &&
tpindex > pindex)
swap_pager_freespace(object, pindex,
tpindex - pindex);
if ((pindex = tpindex) == end)
break;
} else if ((m = vm_page_lookup(tobject, tpindex)) == NULL) {
if (advice == MADV_FREE && tobject->type == OBJT_SWAP)
swap_pager_freespace(tobject, tpindex, 1);
/*
* next object
* Prepare to search the next object in the chain.
*/
backing_object = tobject->backing_object;
if (backing_object == NULL)
@ -1145,11 +1157,13 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
VM_OBJECT_WUNLOCK(tobject);
tobject = backing_object;
goto shadowlookup;
} else if (m->valid != VM_PAGE_BITS_ALL)
goto unlock_tobject;
}
/*
* If the page is not in a normal state, skip it.
*/
if (m->valid != VM_PAGE_BITS_ALL)
goto unlock_tobject;
vm_page_lock(m);
if (m->hold_count != 0 || m->wire_count != 0) {
vm_page_unlock(m);
@ -1160,7 +1174,7 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
KASSERT((m->oflags & VPO_UNMANAGED) == 0,
("vm_object_madvise: page %p is not managed", m));
if (vm_page_busied(m)) {
if (advise == MADV_WILLNEED) {
if (advice == MADV_WILLNEED) {
/*
* Reference the page before unlocking and
* sleeping so that the page daemon is less
@ -1172,21 +1186,18 @@ vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
VM_OBJECT_WUNLOCK(object);
VM_OBJECT_WUNLOCK(tobject);
vm_page_busy_sleep(m, "madvpo", false);
m = NULL;
VM_OBJECT_WLOCK(object);
goto relookup;
}
if (advise == MADV_WILLNEED) {
vm_page_activate(m);
} else {
vm_page_advise(m, advise);
}
vm_page_advise(m, advice);
vm_page_unlock(m);
if (advise == MADV_FREE && tobject->type == OBJT_SWAP)
if (advice == MADV_FREE && tobject->type == OBJT_SWAP)
swap_pager_freespace(tobject, tpindex, 1);
unlock_tobject:
if (tobject != object)
VM_OBJECT_WUNLOCK(tobject);
}
}
VM_OBJECT_WUNLOCK(object);
}

7
sys/vm/vm_page.c
View File

@ -3002,7 +3002,7 @@ vm_page_try_to_free(vm_page_t m)
/*
* vm_page_advise
*
* Deactivate or do nothing, as appropriate.
* Apply the specified advice to the given page.
*
* The object and page must be locked.
*/
@ -3020,8 +3020,11 @@ vm_page_advise(vm_page_t m, int advice)
* would result in a page fault on a later access.
*/
vm_page_undirty(m);
else if (advice != MADV_DONTNEED)
else if (advice != MADV_DONTNEED) {
if (advice == MADV_WILLNEED)
vm_page_activate(m);
return;
}
/*
* Clear any references to the page. Otherwise, the page daemon will