X bench for fallocate on tmpfs

tmpfs/.gitignore

+a.out

tmpfs/1.txt

+host: deco
+os: Linux deco 4.13.0-1-amd64 #1 SMP Debian 4.13.13-1 (2017-11-16) x86_64 GNU/Linux
+BenchmarkTmpfsFallocate/xpage=4K        786432  0.448 µs/op     # t_total: 0.352s
+BenchmarkTmpfsFallocate/xpage=32K       98304   2.653 µs/op     # t_total: 0.261s
+BenchmarkTmpfsFallocate/xpage=256K      12288   20.263 µs/op    # t_total: 0.249s
+BenchmarkTmpfsFallocate/xpage=2048K     1536    161.343 µs/op   # t_total: 0.248s

tmpfs/t_fallocate.c

+// This program benchmarks fallocate on tmpfs
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <sys/user.h>
+#include <sys/mman.h>
+
+// microtime returns current time as double
+double microtime() {
+	int err;
+	struct timeval tv;
+
+	err = gettimeofday(&tv, NULL);
+	if (err == -1) {
+		perror("gettimeofday");
+		abort();
+	}
+
+	return tv.tv_sec + 1E-6 * tv.tv_usec;
+}
+
+int bench_tmpfs_fallocate(size_t xpagesize) {
+	int fd, err, i;
+	double Tstart, Tend;
+
+	fd = open("/dev/shm/y.dat", O_RDWR | O_CREAT | O_TRUNC, 0666);
+	if (fd == -1) {
+		perror("open");
+		abort();
+	}
+
+	size_t filesize = (3*1024*1024*1024ULL); // whole file size
+	//size_t xpagesize = 1 * PAGE_SIZE;
+	//size_t xpagesize = 512 * PAGE_SIZE;
+	size_t niter = filesize / xpagesize;
+
+	err = ftruncate(fd, filesize);
+	if (err == -1) {
+		perror("ftruncate");
+		abort();
+	}
+
+	Tstart = microtime();
+	for (i=0; i<niter; i++) {
+		err = fallocate(fd, /*mode*/0, i*xpagesize, xpagesize);
+		if (err == -1) {
+			perror("fallocate");
+			abort();
+		}
+	}
+	Tend = microtime();
+
+	printf("BenchmarkTmpfsFallocate/xpage=%ldK\t%ld\t%.3lf µs/op\t# t_total: %.3lfs\n",
+			xpagesize / 1024, niter, (Tend - Tstart) * 1E6 / niter, (Tend - Tstart));
+
+	err = close(fd);
+	if (err == -1) {
+		perror("close");
+		abort();
+	}
+
+	return 0;
+}
+
+
+int main() {
+	bench_tmpfs_fallocate(1*PAGE_SIZE);
+	bench_tmpfs_fallocate(8*PAGE_SIZE);
+	bench_tmpfs_fallocate(64*PAGE_SIZE);
+	bench_tmpfs_fallocate(512*PAGE_SIZE);
+}