Alan Cox de6c3db01f Simplify the reference counting of page table pages. Specifically, use ... the page table page's wired count rather than its hold count to contain the reference count. My rationale for this change is based on several factors: 1. The machine-independent and pmap layers used the same hold count field in subtly different ways. The machine-independent layer uses the hold count to implement a form of ephemeral wiring that is used by pipes, physio, etc. In other words, subsystems where we wish to temporarily block a page from being swapped out while it is mapped into the kernel's address space. Such pages are never removed from the page queues. Instead, the page daemon recognizes a non-zero hold count to mean "hands off this page." In contrast, page table pages are never in the page queues; they are wired from birth to death. The hold count was being used as a kind of reference count, specifically, the number of valid page table entries within the page. Not surprisingly, these two different uses imply different synchronization rules: in the machine- independent layer access to the hold count requires the page queues lock; whereas in the pmap layer the pmap lock is required. Thus, continued use by the pmap layer of vm_page_unhold(), which asserts that the page queues lock is held, made no sense. 2. _pmap_unwire_pte_hold() was too forgiving in its handling of the wired count. An unexpected wired count on a page table page was ignored and the underlying page leaked. 3. In a word, microoptimization. Using the wired count exclusively, rather than a combination of the wired and hold counts, makes the code slightly smaller and faster. Reviewed by: tegge@		2004-09-19 21:20:01 +00:00
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alpha	Simplify the reference counting of page table pages. Specifically, use	2004-09-19 21:20:01 +00:00
compile	Don't need the .keep_me files. Obrien and I committed past each other.	2001-07-01 23:35:44 +00:00
conf	Add nge. (I've used one for about a week in an XP1000.)	2004-09-11 07:26:50 +00:00
include	The previous commit, roughly one and a half years ago removed the	2004-09-10 05:00:27 +00:00
isa	Add new a function isa_dma_init() which returns an errno when it fails	2004-09-15 12:09:50 +00:00
linux	Give setrunqueue() and sched_add() more of a clue as to	2004-09-01 02:11:28 +00:00
mcbus	Catch up with __RMAN_RESOURCE_VISIBLE enough to get GENERIC to build	2004-07-01 15:07:27 +00:00
osf1	Regenerate after fcntl() wrappers were marked MP safe.	2004-08-24 20:24:34 +00:00
pci	In alpha_pci_alloc_resource(), when allocating a memory resource,	2004-08-29 19:07:14 +00:00
tlsb	Allocate tty at attach time instead of open time.	2004-09-17 11:04:57 +00:00
Makefile	Add a dopey makefile to do the tags dance, which is probably not perfect	2000-12-31 23:26:34 +00:00