Re: [PATCH 0/1] mm, shmem: map few pages around fault address if they are in page cache

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 28 Feb 2014 16:35:16 -0800 Ning Qu <quning@gmail.com> wrote:

> Sorry about my fault about the experiments, here is the real one.
> 
> Btw, apparently, there are still some questions about the results and
> I will sync with Kirill about his test command line.
> 
> Below is just some simple experiment numbers from this patch, let me know if
> you would like more:
> 
> Tested on Xeon machine with 64GiB of RAM, using the current default fault
> order 4.
> 
> Sequential access 8GiB file
>                         Baseline        with-patch
> 1 thread
>     minor fault         8,389,052    4,456,530
>     time, seconds    9.55            8.31

The numbers still seem wrong.  I'd expect to see almost exactly 2M minor
faults with this test.

Looky:

#include <sys/mman.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define G (1024 * 1024 * 1024)

int main(int argc, char *argv[])
{
	char *p;
	int fd;
	unsigned long idx;
	int sum = 0;

	fd = open("foo", O_RDONLY);
	if (fd < 0) {
		perror("open");
		exit(1);
	}
	p = mmap(NULL, 1 * G, PROT_READ, MAP_PRIVATE, fd, 0);
	if (p == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}

	for (idx = 0; idx < 1 * G; idx += 4096)
		sum += p[idx];
	printf("%d\n", sum);
	exit(0);
}

z:/home/akpm> /usr/bin/time ./a.out
0
0.05user 0.33system 0:00.38elapsed 99%CPU (0avgtext+0avgdata 4195856maxresident)k
0inputs+0outputs (0major+262264minor)pagefaults 0swaps

z:/home/akpm> dc
16o
262264 4 * p
1001E0

That's close!

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