riscv: optimize MADV_WILLNEED on existing superpages

Specifically, avoid pointless calls to pmap_enter_quick_locked() when
madvise(MADV_WILLNEED) is applied to an existing superpage mapping.

1d5ebad06c20 made the change for amd64 and arm64.

Reviewed by:	markj, alc
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D36563

1 files changed, 31 insertions, 20 deletions

diff --git a/sys/riscv/riscv/pmap.c b/sys/riscv/riscv/pmap.c
index aa9eb5255c82..69f2a9ab1522 100644
--- a/sys/riscv/riscv/pmap.c
+++ b/sys/riscv/riscv/pmap.c
@@ -3120,13 +3120,12 @@ out:
 }
 
 /*
- * Tries to create a read- and/or execute-only 2MB page mapping.  Returns true
- * if successful.  Returns false if (1) a page table page cannot be allocated
- * without sleeping, (2) a mapping already exists at the specified virtual
- * address, or (3) a PV entry cannot be allocated without reclaiming another
- * PV entry.
+ * Tries to create a read- and/or execute-only 2MB page mapping.  Returns
+ * KERN_SUCCESS if the mapping was created.  Otherwise, returns an error
+ * value.  See pmap_enter_l2() for the possible error values when "no sleep",
+ * "no replace", and "no reclaim" are specified.
  */
-static bool
+static int
 pmap_enter_2mpage(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
     struct rwlock **lockp)
 {
@@ -3144,18 +3143,20 @@ pmap_enter_2mpage(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
 	if (va < VM_MAXUSER_ADDRESS)
 		new_l2 |= PTE_U;
 	return (pmap_enter_l2(pmap, va, new_l2, PMAP_ENTER_NOSLEEP |
-	    PMAP_ENTER_NOREPLACE | PMAP_ENTER_NORECLAIM, NULL, lockp) ==
-	    KERN_SUCCESS);
+	    PMAP_ENTER_NOREPLACE | PMAP_ENTER_NORECLAIM, NULL, lockp));
 }
 
 /*
  * Tries to create the specified 2MB page mapping.  Returns KERN_SUCCESS if
- * the mapping was created, and either KERN_FAILURE or KERN_RESOURCE_SHORTAGE
- * otherwise.  Returns KERN_FAILURE if PMAP_ENTER_NOREPLACE was specified and
- * a mapping already exists at the specified virtual address.  Returns
- * KERN_RESOURCE_SHORTAGE if PMAP_ENTER_NOSLEEP was specified and a page table
- * page allocation failed.  Returns KERN_RESOURCE_SHORTAGE if
- * PMAP_ENTER_NORECLAIM was specified and a PV entry allocation failed.
+ * the mapping was created, and one of KERN_FAILURE, KERN_NO_SPACE, or
+ * KERN_RESOURCE_SHORTAGE otherwise.  Returns KERN_FAILURE if
+ * PMAP_ENTER_NOREPLACE was specified and a 4KB page mapping already exists
+ * within the 2MB virtual address range starting at the specified virtual
+ * address.  Returns KERN_NO_SPACE if PMAP_ENTER_NOREPLACE was specified and a
+ * 2MB page mapping already exists at the specified virtual address.  Returns
+ * KERN_RESOURCE_SHORTAGE if either (1) PMAP_ENTER_NOSLEEP was specified and a
+ * page table page allocation failed or (2) PMAP_ENTER_NORECLAIM was specified
+ * and a PV entry allocation failed.
  *
  * The parameter "m" is only used when creating a managed, writeable mapping.
  */
@@ -3183,11 +3184,19 @@ pmap_enter_l2(pmap_t pmap, vm_offset_t va, pd_entry_t new_l2, u_int flags,
 		KASSERT(l2pg->ref_count > 1,
 		    ("pmap_enter_l2: l2pg's ref count is too low"));
 		if ((flags & PMAP_ENTER_NOREPLACE) != 0) {
-			l2pg->ref_count--;
-			CTR2(KTR_PMAP,
-			    "pmap_enter_l2: failed to replace existing mapping"
-			    " for va %#lx in pmap %p", va, pmap);
-			return (KERN_FAILURE);
+			if ((oldl2 & PTE_RWX) != 0) {
+				l2pg->ref_count--;
+				CTR2(KTR_PMAP,
+				    "pmap_enter_l2: no space for va %#lx"
+				    " in pmap %p", va, pmap);
+				return (KERN_NO_SPACE);
+			} else {
+				l2pg->ref_count--;
+				CTR2(KTR_PMAP, "pmap_enter_l2:"
+				    " failed to replace existing mapping"
+				    " for va %#lx in pmap %p", va, pmap);
+				return (KERN_FAILURE);
+			}
 		}
 		SLIST_INIT(&free);
 		if ((oldl2 & PTE_RWX) != 0)
@@ -3280,6 +3289,7 @@ pmap_enter_object(pmap_t pmap, vm_offset_t start, vm_offset_t end,
 	vm_offset_t va;
 	vm_page_t m, mpte;
 	vm_pindex_t diff, psize;
+	int rv;
 
 	VM_OBJECT_ASSERT_LOCKED(m_start->object);
 
@@ -3293,7 +3303,8 @@ pmap_enter_object(pmap_t pmap, vm_offset_t start, vm_offset_t end,
 		va = start + ptoa(diff);
 		if ((va & L2_OFFSET) == 0 && va + L2_SIZE <= end &&
 		    m->psind == 1 && pmap_ps_enabled(pmap) &&
-		    pmap_enter_2mpage(pmap, va, m, prot, &lock))
+		    ((rv = pmap_enter_2mpage(pmap, va, m, prot, &lock)) ==
+		    KERN_SUCCESS || rv == KERN_NO_SPACE))
 			m = &m[L2_SIZE / PAGE_SIZE - 1];
 		else
 			mpte = pmap_enter_quick_locked(pmap, va, m, prot, mpte,