runtime: add page cache and tests

This change adds a page cache structure which owns a chunk of free pages
at a given base address. It also adds code to allocate to this cache
from the page allocator. Finally, it adds tests for both.

Notably this change does not yet integrate the code into the runtime,
just into runtime tests.

Updates #35112.

Change-Id: Ibe121498d5c3be40390fab58a3816295601670df
Reviewed-on: https://go-review.googlesource.com/c/go/+/196643
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/runtime/mpallocbits.go b/src/runtime/mpallocbits.go
index b460c032bf..669a41e08f 100644
--- a/src/runtime/mpallocbits.go
+++ b/src/runtime/mpallocbits.go
@@ -16,6 +16,11 @@ func (b *pageBits) get(i uint) uint {
 	return uint((b[i/64] >> (i % 64)) & 1)
 }
 
+// block64 returns the 64-bit aligned block of bits containing the i'th bit.
+func (b *pageBits) block64(i uint) uint64 {
+	return b[i/64]
+}
+
 // set sets bit i of pageBits.
 func (b *pageBits) set(i uint) {
 	b[i/64] |= 1 << (i % 64)
@@ -339,6 +344,13 @@ func (b *pallocBits) freeAll() {
 	(*pageBits)(b).clearAll()
 }
 
+// pages64 returns a 64-bit bitmap representing a block of 64 pages aligned
+// to 64 pages. The returned block of pages is the one containing the i'th
+// page in this pallocBits. Each bit represents whether the page is in-use.
+func (b *pallocBits) pages64(i uint) uint64 {
+	return (*pageBits)(b).block64(i)
+}
+
 // findBitRange64 returns the bit index of the first set of
 // n consecutive 1 bits. If no consecutive set of 1 bits of
 // size n may be found in c, then it returns an integer >= 64.