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Improve management of pages moving from the inactive to active queue. Additionally,

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add some much needed comments.
This commit is contained in:
dyson 1997-10-06 02:48:16 +00:00
parent 34e8b1944e
commit 9b2d1fdb85
1 changed files with 94 additions and 21 deletions
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115
sys/vm/vm_pageout.c
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@ -65,7 +65,7 @@
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*
* $Id: vm_pageout.c,v 1.97 1997/07/27 04:49:19 dyson Exp $
* $Id: vm_pageout.c,v 1.98 1997/09/01 03:17:26 bde Exp $
*/
/*
@ -447,7 +447,7 @@ vm_pageout_object_deactivate_pages(map, object, desired, map_remove_only)
rcount = object->resident_page_count;
p = TAILQ_FIRST(&object->memq);
while (p && (rcount-- > 0)) {
int refcount;
int actcount;
if (vm_map_pmap(map)->pm_stats.resident_count <= desired)
return;
next = TAILQ_NEXT(p, listq);
@ -461,17 +461,17 @@ vm_pageout_object_deactivate_pages(map, object, desired, map_remove_only)
continue;
}
refcount = pmap_ts_referenced(VM_PAGE_TO_PHYS(p));
if (refcount) {
actcount = pmap_ts_referenced(VM_PAGE_TO_PHYS(p));
if (actcount) {
p->flags |= PG_REFERENCED;
} else if (p->flags & PG_REFERENCED) {
refcount = 1;
actcount = 1;
}
if ((p->queue != PQ_ACTIVE) &&
(p->flags & PG_REFERENCED)) {
vm_page_activate(p);
p->act_count += refcount;
p->act_count += actcount;
p->flags &= ~PG_REFERENCED;
} else if (p->queue == PQ_ACTIVE) {
if ((p->flags & PG_REFERENCED) == 0) {
@ -586,6 +586,7 @@ vm_pageout_scan()
vm_offset_t size, bigsize;
vm_object_t object;
int force_wakeup = 0;
int actcount;
int vnodes_skipped = 0;
int s;
@ -636,41 +637,87 @@ vm_pageout_scan()
continue;
}
/*
* If the object is not being used, we ignore previous references.
*/
if (m->object->ref_count == 0) {
m->flags &= ~PG_REFERENCED;
pmap_clear_reference(VM_PAGE_TO_PHYS(m));
/*
* Otherwise, if the page has been referenced while in the inactive
* queue, we bump the "activation count" upwards, making it less
* likely that the page will be added back to the inactive queue
* prematurely again. Here we check the page tables (or emulated
* bits, if any), given the upper level VM system not knowing anything
* about existing references.
*/
} else if (((m->flags & PG_REFERENCED) == 0) &&
pmap_ts_referenced(VM_PAGE_TO_PHYS(m))) {
(actcount = pmap_ts_referenced(VM_PAGE_TO_PHYS(m)))) {
vm_page_activate(m);
m->act_count += (actcount + ACT_ADVANCE);
continue;
}
/*
* If the upper level VM system knows about any page references,
* we activate the page. We also set the "activation count" higher
* than normal so that we will less likely place pages back onto the
* inactive queue again.
*/
if ((m->flags & PG_REFERENCED) != 0) {
m->flags &= ~PG_REFERENCED;
#if 0
pmap_clear_reference(VM_PAGE_TO_PHYS(m));
#else
actcount = pmap_ts_referenced(VM_PAGE_TO_PHYS(m));
#endif
vm_page_activate(m);
m->act_count += (actcount + ACT_ADVANCE + 1);
continue;
}
/*
* If the upper level VM system doesn't know anything about the
* page being dirty, we have to check for it again. As far as the
* VM code knows, any partially dirty pages are fully dirty.
*/
if (m->dirty == 0) {
vm_page_test_dirty(m);
} else if (m->dirty != 0) {
m->dirty = VM_PAGE_BITS_ALL;
}
/*
* Invalid pages can be easily freed
*/
if (m->valid == 0) {
vm_page_protect(m, VM_PROT_NONE);
vm_page_free(m);
cnt.v_dfree++;
++pages_freed;
/*
* Clean pages can be placed onto the cache queue.
*/
} else if (m->dirty == 0) {
vm_page_cache(m);
++pages_freed;
/*
* Dirty pages need to be paged out. Note that we clean
* only a limited number of pages per pagedaemon pass.
*/
} else if (maxlaunder > 0) {
int written;
struct vnode *vp = NULL;
object = m->object;
/*
* We don't bother paging objects that are "dead". Those
* objects are in a "rundown" state.
*/
if (object->flags & OBJ_DEAD) {
s = splvm();
TAILQ_REMOVE(&vm_page_queue_inactive, m, pageq);
@ -753,7 +800,6 @@ vm_pageout_scan()
* sure that we will move a minimal amount of pages from active to
* inactive.
*/
page_shortage = (cnt.v_inactive_target + cnt.v_cache_min) -
(cnt.v_free_count + cnt.v_inactive_count + cnt.v_cache_count);
if (page_shortage <= 0) {
@ -763,6 +809,13 @@ vm_pageout_scan()
page_shortage = 1;
}
}
/*
* If the "inactive" loop finds that there is a shortage over and
* above the page statistics variables, then we need to accomodate
* that. This avoids potential deadlocks due to pages being temporarily
* busy for I/O or other types of temporary wiring.
*/
if (addl_page_shortage) {
if (page_shortage < 0)
page_shortage = 0;
@ -772,8 +825,11 @@ vm_pageout_scan()
pcount = cnt.v_active_count;
m = TAILQ_FIRST(&vm_page_queue_active);
while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
int refcount;
/*
* This is a consistancy check, and should likely be a panic
* or warning.
*/
if (m->queue != PQ_ACTIVE) {
break;
}
@ -799,22 +855,32 @@ vm_pageout_scan()
*/
cnt.v_pdpages++;
refcount = 0;
/*
* Check to see "how much" the page has been used.
*/
actcount = 0;
if (m->object->ref_count != 0) {
if (m->flags & PG_REFERENCED) {
refcount += 1;
actcount += 1;
}
refcount += pmap_ts_referenced(VM_PAGE_TO_PHYS(m));
if (refcount) {
m->act_count += ACT_ADVANCE + refcount;
actcount += pmap_ts_referenced(VM_PAGE_TO_PHYS(m));
if (actcount) {
m->act_count += ACT_ADVANCE + actcount;
if (m->act_count > ACT_MAX)
m->act_count = ACT_MAX;
}
}
/*
* Since we have "tested" this bit, we need to clear it now.
*/
m->flags &= ~PG_REFERENCED;
if (refcount && (m->object->ref_count != 0)) {
/*
* Only if an object is currently being used, do we use the
* page activation count stats.
*/
if (actcount && (m->object->ref_count != 0)) {
s = splvm();
TAILQ_REMOVE(&vm_page_queue_active, m, pageq);
TAILQ_INSERT_TAIL(&vm_page_queue_active, m, pageq);
@ -954,7 +1020,7 @@ vm_pageout_page_stats()
m = TAILQ_FIRST(&vm_page_queue_active);
while ((m != NULL) && (pcount-- > 0)) {
int refcount;
int actcount;
if (m->queue != PQ_ACTIVE) {
break;
@ -975,15 +1041,15 @@ vm_pageout_page_stats()
continue;
}
refcount = 0;
actcount = 0;
if (m->flags & PG_REFERENCED) {
m->flags &= ~PG_REFERENCED;
refcount += 1;
actcount += 1;
}
refcount += pmap_ts_referenced(VM_PAGE_TO_PHYS(m));
if (refcount) {
m->act_count += ACT_ADVANCE + refcount;
actcount += pmap_ts_referenced(VM_PAGE_TO_PHYS(m));
if (actcount) {
m->act_count += ACT_ADVANCE + actcount;
if (m->act_count > ACT_MAX)
m->act_count = ACT_MAX;
s = splvm();
@ -992,6 +1058,13 @@ vm_pageout_page_stats()
splx(s);
} else {
if (m->act_count == 0) {
/*
* We turn off page access, so that we have more accurate
* RSS stats. We don't do this in the normal page deactivation
* when the system is loaded VM wise, because the cost of
* the large number of page protect operations would be higher
* than the value of doing the operation.
*/
vm_page_protect(m, VM_PROT_NONE);
vm_page_deactivate(m);
} else {