Redo the page table page allocation on MIPS, as suggested by

alc@.

The UMA zone based allocation is replaced by a scheme that creates
a new free page list for the KSEG0 region, and a new function
in sys/vm that allocates pages from a specific free page list.

This also fixes a race condition introduced by the UMA based page table
page allocation code. Dropping the page queue and pmap locks before
the call to uma_zfree, and re-acquiring them afterwards  will introduce
a race condtion(noted by alc@).

The changes are :
- Revert the earlier changes in MIPS pmap.c that added UMA zone for
page table pages.
- Add a new freelist VM_FREELIST_HIGHMEM to MIPS vmparam.h for memory that
is not directly mapped (in 32bit kernel). Normal page allocations will first
try the HIGHMEM freelist and then the default(direct mapped) freelist.
- Add a new function 'vm_page_t vm_page_alloc_freelist(int flind, int
order, int req)' to vm/vm_page.c to allocate a page from a specified
freelist. The MIPS page table pages will be allocated using this function
from the freelist containing direct mapped pages.
- Move the page initialization code from vm_phys_alloc_contig() to a
new function vm_page_alloc_init(), and use this function to initialize
pages in vm_page_alloc_freelist() too.
- Split the  function vm_phys_alloc_pages(int pool, int order) to create
vm_phys_alloc_freelist_pages(int flind, int pool, int order), and use
this function from both vm_page_alloc_freelist() and vm_phys_alloc_pages().

Reviewed by:	alc

1 files changed, 89 insertions, 0 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 348ab99..44b801e 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1355,6 +1355,95 @@ vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int req)
 }
 
 /*
+ * Initialize a page that has been freshly dequeued from a freelist.
+ * The caller has to drop the vnode returned, if it is not NULL.
+ *
+ * To be called with vm_page_queue_free_mtx held.
+ */
+struct vnode *
+vm_page_alloc_init(vm_page_t m)
+{
+	struct vnode *drop;
+	vm_object_t m_object;
+
+	KASSERT(m->queue == PQ_NONE,
+	    ("vm_page_alloc_init: page %p has unexpected queue %d",
+	    m, m->queue));
+	KASSERT(m->wire_count == 0,
+	    ("vm_page_alloc_init: page %p is wired", m));
+	KASSERT(m->hold_count == 0,
+	    ("vm_page_alloc_init: page %p is held", m));
+	KASSERT(m->busy == 0,
+	    ("vm_page_alloc_init: page %p is busy", m));
+	KASSERT(m->dirty == 0,
+	    ("vm_page_alloc_init: page %p is dirty", m));
+	KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
+	    ("vm_page_alloc_init: page %p has unexpected memattr %d",
+	    m, pmap_page_get_memattr(m)));
+	mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
+	drop = NULL;
+	if ((m->flags & PG_CACHED) != 0) {
+		m->valid = 0;
+		m_object = m->object;
+		vm_page_cache_remove(m);
+		if (m_object->type == OBJT_VNODE &&
+		    m_object->cache == NULL)
+			drop = m_object->handle;
+	} else {
+		KASSERT(VM_PAGE_IS_FREE(m),
+		    ("vm_page_alloc_init: page %p is not free", m));
+		KASSERT(m->valid == 0,
+		    ("vm_page_alloc_init: free page %p is valid", m));
+		cnt.v_free_count--;
+	}
+	if (m->flags & PG_ZERO)
+		vm_page_zero_count--;
+	/* Don't clear the PG_ZERO flag; we'll need it later. */
+	m->flags = PG_UNMANAGED | (m->flags & PG_ZERO);
+	m->oflags = 0;
+	/* Unmanaged pages don't use "act_count". */
+	return (drop);
+}
+
+/*
+ * 	vm_page_alloc_freelist:
+ * 
+ *	Allocate a page from the specified freelist with specified order.
+ *	Only the ALLOC_CLASS values in req are honored, other request flags
+ *	are ignored.
+ */
+vm_page_t
+vm_page_alloc_freelist(int flind, int order, int req)
+{
+	struct vnode *drop;
+	vm_page_t m;
+	int page_req;
+
+	m = NULL;
+	page_req = req & VM_ALLOC_CLASS_MASK;
+	mtx_lock(&vm_page_queue_free_mtx);
+	/*
+	 * Do not allocate reserved pages unless the req has asked for it.
+	 */
+	if (cnt.v_free_count + cnt.v_cache_count > cnt.v_free_reserved ||
+	    (page_req == VM_ALLOC_SYSTEM && 
+	    cnt.v_free_count + cnt.v_cache_count > cnt.v_interrupt_free_min) ||
+	    (page_req == VM_ALLOC_INTERRUPT &&
+	    cnt.v_free_count + cnt.v_cache_count > 0)) {
+		m = vm_phys_alloc_freelist_pages(flind, VM_FREEPOOL_DIRECT, order);
+	}
+	if (m == NULL) {
+		mtx_unlock(&vm_page_queue_free_mtx);
+		return (NULL);
+	}
+	drop = vm_page_alloc_init(m);
+	mtx_unlock(&vm_page_queue_free_mtx);
+	if (drop)
+		vdrop(drop);
+	return (m);
+}
+
+/*
  *	vm_wait:	(also see VM_WAIT macro)
  *
  *	Block until free pages are available for allocation