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In general, we call pmap_remove_all() before calling vm_page_cache(). So,

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the call to pmap_remove_all() within vm_page_cache() is usually redundant.
This change eliminates that call to pmap_remove_all() and introduces a
call to pmap_remove_all() before vm_page_cache() in the one place where
it didn't already exist.

When iterating over a paging queue, if the object containing the current
page has a zero reference count, then the page can't have any managed
mappings.  So, a call to pmap_remove_all() is pointless.

Change a panic() call in vm_page_cache() to a KASSERT().

MFC after:	6 weeks
This commit is contained in:
Alan Cox 2012-11-01 16:20:02 +00:00
parent cd9e9d1bc2
commit 9fc4739d2a
2 changed files with 13 additions and 28 deletions
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6
sys/vm/vm_page.c
View File

@ -2277,9 +2277,9 @@ vm_page_cache(vm_page_t m)
if ((m->oflags & (VPO_UNMANAGED | VPO_BUSY)) || m->busy ||
m->hold_count || m->wire_count)
panic("vm_page_cache: attempting to cache busy page");
pmap_remove_all(m);
if (m->dirty != 0)
panic("vm_page_cache: page %p is dirty", m);
KASSERT(!pmap_page_is_mapped(m),
("vm_page_cache: page %p is mapped", m));
KASSERT(m->dirty == 0, ("vm_page_cache: page %p is dirty", m));
if (m->valid == 0 || object->type == OBJT_DEFAULT ||
(object->type == OBJT_SWAP &&
!vm_pager_has_page(object, m->pindex, NULL, NULL))) {

35
sys/vm/vm_pageout.c
View File

@ -594,7 +594,7 @@ vm_pageout_launder(int queue, int tries, vm_paddr_t low, vm_paddr_t high)
continue;
}
vm_page_test_dirty(m);
if (m->dirty == 0)
if (m->dirty == 0 && object->ref_count != 0)
pmap_remove_all(m);
if (m->dirty != 0) {
vm_page_unlock(m);
@ -1059,31 +1059,16 @@ vm_pageout_scan(int pass)
}
/*
* If the upper level VM system does not believe that the page
* is fully dirty, but it is mapped for write access, then we
* consult the pmap to see if the page's dirty status should
* be updated.
* If the page appears to be clean at the machine-independent
* layer, then remove all of its mappings from the pmap in
* anticipation of placing it onto the cache queue. If,
* however, any of the page's mappings allow write access,
* then the page may still be modified until the last of those
* mappings are removed.
*/
if (m->dirty != VM_PAGE_BITS_ALL &&
pmap_page_is_write_mapped(m)) {
/*
* Avoid a race condition: Unless write access is
* removed from the page, another processor could
* modify it before all access is removed by the call
* to vm_page_cache() below. If vm_page_cache() finds
* that the page has been modified when it removes all
* access, it panics because it cannot cache dirty
* pages. In principle, we could eliminate just write
* access here rather than all access. In the expected
* case, when there are no last instant modifications
* to the page, removing all access will be cheaper
* overall.
*/
if (pmap_is_modified(m))
vm_page_dirty(m);
else if (m->dirty == 0)
pmap_remove_all(m);
}
vm_page_test_dirty(m);
if (m->dirty == 0 && object->ref_count != 0)
pmap_remove_all(m);
if (m->valid == 0) {
/*