[CRIU] How should pre-dump work?

[Mike Rapoprt]

On July 18, 2017 3:59:40 PM GMT+03:00, Michael Holzheu <holzheu at linux.vnet.ibm.com> wrote:
>According to https://criu.org/Iterative_migration I tested the
>CRIU pre-dump feature.
>
>I did the following steps:
>
>1) Compile test program that fills 512MB memory
>-----------------------------------------------
>
>~# cat predump_test.c 
>#include <stdio.h>
>#include <string.h>
>#include <unistd.h>
>
>/* Define 512 MB buffer */
>char buf[(1 << 20) * 512];
>
>int main(void)
>{
>        /* Fill buffer */
>        memset(buf, 1, sizeof(buf));
>        /* Loop */
>        while (1) {
>                fprintf(stderr, ".");
>                sleep(5);
>        }
>        return 0;
>}
>
>~# gcc -o predump_test predump_test.c
>~# ./predump_test
>
>~# mkdir A B C
>
>2) Do 1st pre-dump
>------------------
>
># criu pre-dump -t $(pgrep predump_test) --shell-job --images-dir A/
>
>root at r3545010~# du -h A/*
>4.0K    A/irmap-cache
>8.0K    A/pagemap-27013.img
>513M    A/pages-1.img
>4.0K    A/stats-dump
>
>We get the expected 513 MB "pages-1.img" file.
>
>3) Do 2nd pre-dump
>------------------
>
>~# criu pre-dump -t $(pgrep predump_test) --shell-job --images-dir B/
>--prev-images-dir ../A
>
>~# du -h B/*
>4.0K    B/irmap-cache
>4.0K    B/pagemap-27013.img
>24K     B/pages-1.img
>0       B/parent
>4.0K    B/stats-dump
>
>As expected the "pages-1.img" file is small.
>
>4) Do final dump
>----------------
>
>~# criu dump -t $(pgrep predump_test) --shell-job --images-dir C/
>--prev-images-dir ../B

I think you also should add --track-mem option

>~# du -h C/*
>8.0K    C/cgroup.img
>4.0K    C/core-27013.img
>4.0K    C/fdinfo-2.img
>4.0K    C/files.img
>4.0K    C/fs-27013.img
>4.0K    C/ids-27013.img
>4.0K    C/inventory.img
>4.0K    C/mm-27013.img
>8.0K    C/pagemap-27013.img
>513M    C/pages-1.img
>0       C/parent
>4.0K    C/pstree.img
>4.0K    C/stats-dump
>4.0K    C/tty-info.img
>4.0K    C/tty.img
>
>We get again a 513 MB "pages-1.img" file - why?
>
>I get the same results on s390 and on x86.
>
>System information
>------------------
>CRIU git version: 1f734612779d076d597dadbbf4ef9256c89d1241 (criu-dev)
>CRIU version    : Version: 3.2
>Distro version  : VERSION="16.04.1 LTS (Xenial Xerus)"
>Kernel version  : Linux r3545010 4.8.0-34-generic #36~16.04.1-Ubuntu
>SMP Wed Dec 21 19:00:07 UTC 2016 s390x s390x
>
>Best Regards,
>Michael
>
>_______________________________________________
>CRIU mailing list
>CRIU at openvz.org
>https://lists.openvz.org/mailman/listinfo/criu

-- 
Sincerely yours,
Mike.