No comment on this?  Was it just that I posted it during the VM summit?

On Mon, Aug 09, 2010 at 09:30:00AM -0400, Matthew Wilcox wrote:
quoted text
> 
> This testcase shows some odd behaviour from the Linux VM.
> 
> It creates a 1TB sparse file, mmaps it, and randomly reads locations 
> in it.  Due to the file being entirely sparse, the VM allocates new pages
> and zeroes them.  Initially, it runs very fast, taking on the order of
> 2.7 to 4us per page fault.  Eventually, the VM runs out of free pages,
> and starts doing huge amounts of work trying to figure out which of
> these clean pages to throw away.  In my testing with a 6GB machine 
> and 2.9GHz CPU, one in every 15,000 page faults takes over a second, 
> and one in every 40,000 page faults take over seven seconds!
> 
> This test-case demonstrates a problem that occurs with a read-mostly 
> mmap of a file on very fast media.  I wouldn't like to see a solution
> that special-cases zeroed pages.  I think userspace has done its part
> to tell the kernel what's it's doing by calling madvise(MADV_RANDOM).
> This ought to be enough to hint to the kernel that it should be eagerly
> throwing away pages in this VMA.
> 
> 
> /*
>  * Copyright (c) 2010, Intel Corporation
>  * All rights reserved.
>  *
>  * Redistribution and use in source and binary forms, with or without
>  * modification, are permitted provided that the following conditions are met:
>  *
>  *  * Redistributions of source code must retain the above copyright notice,
>  *    this list of conditions and the following disclaimer.
>  *  * Redistributions in binary form must reproduce the above copyright notice,
>  *    this list of conditions and the following disclaimer in the documentation
>  *    and/or other materials provided with the distribution.
>  *  * Neither the name of Intel Corporation nor the names of its contributors
>  *    may be used to endorse or promote products derived from this software
>  *    without specific prior written permission.
>  *
>  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
>  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
>  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
>  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
>  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
>  * POSSIBILITY OF SUCH DAMAGE.
>  */
> 
> #include <assert.h>
> #include <errno.h>
> #include <fcntl.h>
> #include <math.h>
> #include <pthread.h>
> #include <signal.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/mman.h>
> #include <sys/stat.h>
> #include <sys/time.h>
> #include <sys/types.h>
> #include <unistd.h>
> 
> #define rdtscll(val) do { \
>      unsigned int __a,__d; \
>      asm volatile("rdtsc" : "=a" (__a), "=d" (__d)); \
>      (val) = ((unsigned long)__a) | (((unsigned long)__d)<<32); \
> } while(0)
> 
> 
> #define MAX_FILE_SIZE	((off_t)1024 * 1024 * 1024 * 1024)
> #define	MAX_FILE_IOS	16384
> #define	MAX_LATENCY	10000000		// usecs
> 
> #define NUM_IOS		1024
> #define IO_SIZE		4096
> #define BUFFER_SIZE	(1024 * 1024)
> 
> pthread_t tid;
> double 	cpu_clock;
> long long unsigned cpu_start, cpu_stop;
> 
> void *mmap_test(void *arg);
> void die ();
> 
> static const char usage_cmds[] =
> "usage: %s [options]\n"
> "cmd line options:\n"
> "    -f	file_name	Read from File named 'file_name'\n"
> "    -a	file_size	File of 'file_size' Bytes/thread\n"
> "    -b	buffer_size	Write/Read into/from buffer of 'buffer_size' Bytes/thread\n"
> "    -n	num_file_ios	Process 'num_file_ios' IOs\n"
> "    -s	io_size		IO Size = 'io_size' Bytes\n"
> "    -l max_latency     Show latency stats based on usecs of max_latency\n"
> ;
> 
> void usage(const char *program)
> {
> 	fprintf(stderr, usage_cmds, program);
> }
> 
> off_t file_size = MAX_FILE_SIZE;	// -a
> long long unsigned int buffer_size = BUFFER_SIZE;	// -b
> char *filename = "sparse-file";			// -f
> int	num_file_ios = NUM_IOS;		// -n
> int	max_latency = MAX_LATENCY;	// -l
> int	io_size = IO_SIZE;		// -s
> long long unsigned int   latency_limit;
> 
> int main(int argc, char **argv)
> {
> 	pthread_attr_t 	attr;
> 	cpu_set_t             mask;
> 	FILE *proc;
> 	char buf[256];
> 	double mhz = 0.0;
> 
> 	while (1) {
> 	    int option = getopt(argc, argv, "a:b:f:h:l:n:p:s:");
> 		if (option == -1) {
> 		    break;
> 		}
> 	    switch (option) {
> 		case 'a':
> 		    file_size = strtoul(optarg, NULL, 0);
> 		    printf("a: file_size:%ld Bytes :%ld MB\n", file_size, file_size/(1024*1024));
> 		    break;
> 		case 'b':
> 		    buffer_size = strtoul(optarg, NULL, 0);
> 		    printf("b: buffer_size:%lld Bytes\n", buffer_size);
> 		    break;
> 		case 'f':
> 	    	    filename = optarg;
> 		    printf("f: filename:%s\n", filename);
> 		    break;
> 		case 'h':
> 		    printf("h: options\n");
> 		    goto help;
> 		case 'l':
> 		    max_latency = strtoul(optarg, NULL, 0);
> 		    printf("l: latency stats based on max latency:%d\n", max_latency);
> 		    break;
> 		case 'n':
> 		    num_file_ios = strtoul(optarg, NULL, 0);
> 		    printf("n: num_file_ios:%d\n", num_file_ios);
> 		    if (num_file_ios > MAX_FILE_IOS) {
> 			printf("-n %d Entered > MAX_FILE_IOS:%d\n", num_file_ios, MAX_FILE_IOS);
> 			exit(1);
> 		    }
> 		    break;
> 		case 's':
> 		    io_size = strtoul(optarg, NULL, 0);
> 		    printf("s: io_size:%d Bytes\n", io_size);
> 		    break;
> 		default:
> 		help:
> 		    usage(argv[0]);
> 		    printf("default:\n");
> 		    exit(1);
> 	    }
> 	}
> 
> 	proc = fopen("/proc/cpuinfo", "r");
> 	if (!proc)
> 		return 0.0;
> 
> 	while (fgets(buf, sizeof buf, proc)) {
> 		double cpu;
> 
> 		if (sscanf(buf, "cpu MHz : %lf", &cpu) != 1)
> 			continue;
> 		if (mhz == 0.0) {
> 			mhz = cpu;
> 			continue;
> 		}
> 		if (mhz != cpu) {
> 			fprintf(stderr,
> 				"Conflicting CPU frequency values: %lf != %lf\n",
> 				mhz, cpu);
> 			return 0.0;
> 		}
> 	}
> 	fclose(proc);
> 	printf("CPU Clock Freq from /proc/cpuinfo:%.4f\n", mhz);
> //
> // Measure CPU Core Frequnecy over 5 second period
> //
> 	printf("Measuring CPU Frequency......:");
> 	rdtscll(cpu_start);
> 	usleep(5000000);
> 	rdtscll(cpu_stop);
> 	cpu_clock = (double)((double)(cpu_stop-cpu_start))/(double)5.0;
> 	printf("%.3f\n", cpu_clock);
> 	latency_limit = (long long unsigned int) (cpu_clock*max_latency/1000000);
> 	printf("latency_limit:%llu cycles or %d usecs\n", latency_limit, max_latency);
> 
> 	pthread_attr_init (&attr);
> 	pthread_attr_setscope (&attr, PTHREAD_SCOPE_SYSTEM);
> 	pthread_attr_setstacksize (&attr, (size_t) (1024*1024));
> 
> 	if (pthread_create(&tid, &attr, mmap_test, (void *)(long) 0) != 0) {
> 		die("Thread create failed!");
> 	}
> 
> 	CPU_ZERO(&mask);
> 	CPU_SET(0, &mask);
> 	if (pthread_setaffinity_np(tid, sizeof(mask), &mask) ) {
> 	 	printf("WARNING: could not set CPU Affinity, exit...\n");
> 	 	exit(1);
> 	}
> 
>         pthread_join(tid, NULL);
>         sleep(1);
> 
> 	return 0;
> }
> 
> 
> void die(char *string)
> {
> 	fprintf(stderr, "\nmmap_test: %s\n", string);
> 	exit(1);
> }
> 
> void *mmapfile(char *fname, off_t size, int *filed)
> {
> 	int fd;
> 	void *file_addr;
> 	struct stat statbuf;
> 
> 	fd = open(fname, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
> 	*filed = fd;
> 	if (fd < 0) {
>     		fprintf(stderr, "unable to open %s to get an FD:%s\n", fname, strerror(errno));
> 		exit(1);
> 	}
> 
> 	fstat(fd, &statbuf);
> 	if (statbuf.st_size < size)
> 		ftruncate(fd, size);
> 
> 	file_addr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> 	if (file_addr == MAP_FAILED) {
>     		fprintf(stderr, "datafile mmap failed: %s\n", strerror(errno));
> 		exit(1);
> 	}
> 
> 	madvise(file_addr, size, MADV_RANDOM);
> 	return file_addr;
> }
> 
> void create_offsets(off_t *offset_buf, int threadnum)
> {
> 	int i, curr_time;
> 
> 	curr_time = time(NULL);
>         srandom(curr_time / (threadnum + 1));
> 
> 	for (i = 0; i < num_file_ios; i++) {
> 		double random1 = ((double)(rand()%(RAND_MAX)) / RAND_MAX);
> 		offset_buf[i] = file_size * random1;
> 		offset_buf[i] = offset_buf[i] / io_size * io_size;
> 	}
> }
> 
> void *mmap_test(void *arg)
> {
> 	int threadnum = (long) arg;
> 	int fd;
> 	char *file_ptr, *file_addr;
> 	char *buf_ptr, *buf_addr = NULL;
> 	int i, j, ios;
> 	off_t offset_buf[MAX_FILE_IOS];
> 	unsigned long long latency_start, latency_stop;
> 
> 	posix_memalign((void *)&buf_addr, 4096, buffer_size);
> 
> 	file_addr = mmapfile(filename, file_size, &fd);
> 
> 	ios = buffer_size/io_size;
> 
> 	create_offsets(offset_buf, threadnum);
> 
> 	for (j = 0; j < num_file_ios; j++) {
> 		buf_ptr = buf_addr;
> 		file_ptr = file_addr + offset_buf[j];
>  
> 		for (i = 0; i < ios; i++) {
> 			rdtscll(latency_start);
> 			*buf_ptr = *(char *)file_ptr;
> 			rdtscll(latency_stop);
> 			printf("%lld\n", latency_stop - latency_start);
> 			buf_ptr += io_size;
> 			file_ptr += io_size;
> 		}
> 	}
> 
> 	close(fd);
> 	munmap(file_addr, file_size);
> 	free(buf_addr);
> 
> 	pthread_exit(NULL);
> 	return 0;
> }
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