unix: add linux cachestat system call

The cachestat system call is an alternative to mincore that offers more
extensive page cache statistics, aiming to enhance scalability. It was added
on Linux 6.5.

Fixes golang/go#61917

Change-Id: If1b6b96f859dd6bf09f1a0c048abfa743a42c540
GitHub-Last-Rev: d18fbb9
GitHub-Pull-Request: #176
Reviewed-on: https://go-review.googlesource.com/c/sys/+/533242
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

unix/linux/types.go

@@ -461,6 +461,20 @@ struct my_can_bittiming_const {
 
 struct riscv_hwprobe {};
 #endif
+
+// copied from /usr/include/uapi/linux/mman.h
+struct cachestat_range {
+	__u64 off;
+	__u64 len;
+};
+
+struct cachestat {
+	__u64 nr_cache;
+	__u64 nr_dirty;
+	__u64 nr_writeback;
+	__u64 nr_evicted;
+	__u64 nr_recently_evicted;
+};
 */
 import "C"
 
@@ -5813,3 +5827,6 @@ const (
 type SchedAttr C.struct_sched_attr
 
 const SizeofSchedAttr = C.sizeof_struct_sched_attr
+
+type Cachestat_t C.struct_cachestat
+type CachestatRange C.struct_cachestat_range

unix/syscall_linux.go

@@ -2482,3 +2482,5 @@ func SchedGetAttr(pid int, flags uint) (*SchedAttr, error) {
 	}
 	return attr, nil
 }
+
+//sys	Cachestat(fd uint, crange *CachestatRange, cstat *Cachestat_t, flags uint) (err error)