Make amaps use less kernel memory (2nd try)

The original diff would crash at least i386 and powerpc, as spotted by
guenther@ The reason was an incorrect use of sizeof in amap_lookups().

Confirmation that powerpc works by mpi@ and mglocker@

"throw it in" deraadt@

Original commit message:

This is achieved by grouping amap slots into chunks that are allocated
on-demand by pool(9). Endless "fltamapcopy" loops because of kmem
shortage should be solved now. The kmem savings are also important to later
enable vmm(4) to use larged shared memory mappings for guest VM RAM.

This adapts libkvm also because the amap structure layout has changed.

Testing and fix of libkvm glitch in initial diff by tb@
Feedback and "time to get this in" kettenis@

1 files changed, 53 insertions, 11 deletions

diff --git a/lib/libkvm/kvm_proc.c b/lib/libkvm/kvm_proc.c
index bf9230c6116..0a027bb4b4e 100644
--- a/lib/libkvm/kvm_proc.c
+++ b/lib/libkvm/kvm_proc.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kvm_proc.c,v 1.55 2016/05/22 22:52:01 guenther Exp $	*/
+/*	$OpenBSD: kvm_proc.c,v 1.56 2016/05/26 13:37:26 stefan Exp $	*/
 /*	$NetBSD: kvm_proc.c,v 1.30 1999/03/24 05:50:50 mrg Exp $	*/
 /*-
  * Copyright (c) 1998 The NetBSD Foundation, Inc.
@@ -108,6 +108,56 @@ static int	proc_verify(kvm_t *, const struct kinfo_proc *);
 static void	ps_str_a(struct ps_strings *, u_long *, int *);
 static void	ps_str_e(struct ps_strings *, u_long *, int *);
 
+static struct vm_anon *
+_kvm_findanon(kvm_t *kd, struct vm_amap *amapp, int slot)
+{
+	u_long addr;
+	int bucket;
+	struct vm_amap amap;
+	struct vm_amap_chunk chunk, *chunkp;
+	struct vm_anon *anonp;
+
+	addr = (u_long)amapp;
+	if (KREAD(kd, addr, &amap))
+		return (NULL);
+
+	/* sanity-check slot number */
+	if (slot > amap.am_nslot)
+		return (NULL);
+
+	if (UVM_AMAP_SMALL(&amap))
+		chunkp = &amapp->am_small;
+	else {
+		bucket = UVM_AMAP_BUCKET(&amap, slot);
+		addr = (u_long)(amap.am_buckets + bucket);
+		if (KREAD(kd, addr, &chunkp))
+			return (NULL);
+
+		while (chunkp != NULL) {
+			addr = (u_long)chunkp;
+			if (KREAD(kd, addr, &chunk))
+				return (NULL);
+
+			if (UVM_AMAP_BUCKET(&amap, chunk.ac_baseslot) !=
+			    bucket)
+				return (NULL);
+			if (slot >= chunk.ac_baseslot &&
+			    slot < chunk.ac_baseslot + chunk.ac_nslot)
+				break;
+
+			chunkp = TAILQ_NEXT(&chunk, ac_list);
+		}
+		if (chunkp == NULL)
+			return (NULL);
+	}
+
+	addr = (u_long)&chunkp->ac_anon[UVM_AMAP_SLOTIDX(slot)];
+	if (KREAD(kd, addr, &anonp))
+		return (NULL);
+
+	return (anonp);
+}
+
 static char *
 _kvm_ureadm(kvm_t *kd, const struct kinfo_proc *p, u_long va, u_long *cnt)
 {
@@ -115,7 +165,6 @@ _kvm_ureadm(kvm_t *kd, const struct kinfo_proc *p, u_long va, u_long *cnt)
 	struct vmspace vm;
 	struct vm_anon *anonp, anon;
 	struct vm_map_entry vme;
-	struct vm_amap amap;
 	struct vm_page pg;
 
 	if (kd->swapspc == 0) {
@@ -153,18 +202,11 @@ _kvm_ureadm(kvm_t *kd, const struct kinfo_proc *p, u_long va, u_long *cnt)
 	if (vme.aref.ar_amap == NULL)
 		return (NULL);
 
-	addr = (u_long)vme.aref.ar_amap;
-	if (KREAD(kd, addr, &amap))
-		return (NULL);
-
 	offset = va - vme.start;
 	slot = offset / kd->nbpg + vme.aref.ar_pageoff;
-	/* sanity-check slot number */
-	if (slot > amap.am_nslot)
-		return (NULL);
 
-	addr = (u_long)amap.am_anon + (offset / kd->nbpg) * sizeof(anonp);
-	if (KREAD(kd, addr, &anonp))
+	anonp = _kvm_findanon(kd, vme.aref.ar_amap, slot);
+	if (anonp == NULL)
 		return (NULL);
 
 	addr = (u_long)anonp;