Re: [fstests PATCH] generic: add test for DAX MAP_SYNC support

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Oct 20, 2017 at 8:29 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> Add a test that exercises DAX's new MAP_SYNC flag.
>
> This test creates a file and writes to it via an mmap(), but never syncs
> via fsync/msync.  This process is tracked via dm-log-writes, then replayed.
>
> If MAP_SYNC is working the dm-log-writes replay will show the test file
> with the same size that we wrote via the mmap() because each allocating
> page fault included an implicit metadata sync.  If MAP_SYNC isn't working
> (which you can test by fiddling with the parameters to mmap()) the file
> will be smaller or missing entirely.
>
> Note that dm-log-writes doesn't track the data that we write via the
> mmap(), so we can't do any data integrity checking.  We can only verify
> that the metadata writes for the page faults happened.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

Looks good. some nit picking...

> ---
>
> For this test to run successfully you'll need both Jan's MAP_SYNC series:
>
> https://www.spinics.net/lists/linux-xfs/msg11852.html
>
> and my series adding DAX support to dm-log-writes:
>
> https://lists.01.org/pipermail/linux-nvdimm/2017-October/012972.html
>
> ---
>  .gitignore            |  1 +
>  common/dmlogwrites    |  1 -
>  src/Makefile          |  3 +-
>  src/t_map_sync.c      | 74 +++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/466     | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/466.out |  3 ++
>  tests/generic/group   |  1 +
>  7 files changed, 158 insertions(+), 2 deletions(-)
>  create mode 100644 src/t_map_sync.c
>  create mode 100755 tests/generic/466
>  create mode 100644 tests/generic/466.out
>
> diff --git a/.gitignore b/.gitignore
> index 2014c08..9fc0695 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -119,6 +119,7 @@
>  /src/t_getcwd
>  /src/t_holes
>  /src/t_immutable
> +/src/t_map_sync
>  /src/t_mmap_cow_race
>  /src/t_mmap_dio
>  /src/t_mmap_fallocate
> diff --git a/common/dmlogwrites b/common/dmlogwrites
> index 247c744..5b57df9 100644
> --- a/common/dmlogwrites
> +++ b/common/dmlogwrites
> @@ -23,7 +23,6 @@ _require_log_writes()
>         [ -z "$LOGWRITES_DEV" -o ! -b "$LOGWRITES_DEV" ] && \
>                 _notrun "This test requires a valid \$LOGWRITES_DEV"
>
> -       _exclude_scratch_mount_option dax
>         _require_dm_target log-writes
>         _require_test_program "log-writes/replay-log"
>  }
> diff --git a/src/Makefile b/src/Makefile
> index 3eb25b1..af7e7e9 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -13,7 +13,8 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
>         multi_open_unlink dmiperf unwritten_sync genhashnames t_holes \
>         t_mmap_writev t_truncate_cmtime dirhash_collide t_rename_overwrite \
>         holetest t_truncate_self t_mmap_dio af_unix t_mmap_stale_pmd \
> -       t_mmap_cow_race t_mmap_fallocate fsync-err t_mmap_write_ro
> +       t_mmap_cow_race t_mmap_fallocate fsync-err t_mmap_write_ro \
> +       t_map_sync
>
>  LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
>         preallo_rw_pattern_writer ftrunc trunc fs_perms testx looptest \
> diff --git a/src/t_map_sync.c b/src/t_map_sync.c
> new file mode 100644
> index 0000000..8190f3c
> --- /dev/null
> +++ b/src/t_map_sync.c
> @@ -0,0 +1,74 @@
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mman.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +#define MiB(a) ((a)*1024*1024)
> +
> +/*
> + * These two defines were added to the kernel via commits entitled
> + * "mm: Define MAP_SYNC and VM_SYNC flags" and
> + * "mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap
> + * flags", respectively.

#ifndef?

> + */
> +#define MAP_SYNC 0x80000
> +#define MAP_SHARED_VALIDATE 0x3
> +
> +void err_exit(char *op)
> +{
> +       fprintf(stderr, "%s: %s\n", op, strerror(errno));
> +       exit(1);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +       int page_size = getpagesize();
> +       int len = MiB(1);
> +       int i, fd, err;
> +       char *data;
> +
> +       if (argc < 2) {
> +               printf("Usage: %s <file>\n", basename(argv[0]));
> +               exit(0);
> +       }
> +
> +       fd = open(argv[1], O_RDWR|O_CREAT, S_IRUSR|S_IWUSR);
> +       if (fd < 0)
> +               err_exit("fd");
> +
> +       ftruncate(fd, 0);

O_TRUNC?

> +       ftruncate(fd, len);
> +
> +       data = mmap(NULL, len, PROT_READ|PROT_WRITE,
> +                       MAP_SHARED_VALIDATE|MAP_SYNC, fd, 0);
> +       if (data == MAP_FAILED)
> +               err_exit("mmap");
> +
> +       /*
> +        * We intentionally don't sync 'fd' manually.  If MAP_SYNC is working
> +        * these allocating page faults will cause the filesystem to sync its
> +        * metadata so that when we replay the dm-log-writes log the test file
> +        * will be 1 MiB in size.
> +        *
> +        * dm-log-writes doesn't track the data that we write via the mmap(),
> +        * so we can't check that, we can only verify that the metadata writes
> +        * happened.
> +        */
> +       for (i = 0; i < len; i+=page_size)
> +               data[i] = 0xff;
> +

Ideally, you would write the mark now (see mark_log() in fsx.c)
Otherwise, what you are testing is not that page faults allocate disk blocks,
but rather that page fault + munmap + close + process exit
allocate disk blocks.
I realize munmap/close are not supposed to sync dirty pages, but better
eliminate this noise from the test.


> +       err = munmap(data, len);
> +       if (err < 0)
> +               err_exit("munmap");
> +
> +       err = close(fd);
> +       if (err < 0)
> +               err_exit("close");
> +
> +       return 0;
> +}
> diff --git a/tests/generic/466 b/tests/generic/466
> new file mode 100755
> index 0000000..f39e6dc
> --- /dev/null
> +++ b/tests/generic/466
> @@ -0,0 +1,77 @@
> +#! /bin/bash
> +# FS QA Test No. 466
> +#
> +# Use md_log_writes to verify that MAP_SYNC actually syncs metadata during
> +# page faults.
> +#
> +#-----------------------------------------------------------------------
> +# Copyright (c) 2017 Intel Corporation.  All Rights Reserved.
> +#
> +# This program is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU General Public License as
> +# published by the Free Software Foundation.
> +#
> +# This program is distributed in the hope that it would be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program; if not, write the Free Software Foundation,
> +# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> +#-----------------------------------------------------------------------
> +#
> +
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +
> +here=`pwd`
> +status=1       # failure is the default!
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +_cleanup()
> +{
> +       _log_writes_cleanup
> +}
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +. ./common/dmlogwrites
> +
> +# remove previous $seqres.full before test
> +rm -f $seqres.full
> +
> +# real QA test starts here
> +_supported_fs generic
> +_supported_os Linux
> +_require_log_writes
> +_require_scratch_dax
> +_require_test_program "t_map_sync"
> +
> +_log_writes_init
> +_log_writes_mkfs >> $seqres.full 2>&1
> +_log_writes_mount -o dax
> +
> +src/t_map_sync $SCRATCH_MNT/test
> +
> +# Unmount the scratch dir and tear down the log writes target
> +_log_writes_mark last

Feel free to use the lousy name I chose for the pre_unmount mark ;-)
but if you follow my suggestion to move the mark into t_map_sync
better call it pre_munmap or something.

> +_log_writes_unmount
> +_log_writes_remove
> +_check_scratch_fs
> +
> +# check pre umount
> +_log_writes_replay_log last
> +_scratch_mount
> +
> +# We should see $SCRATCH_MNT/test as 1MiB in size

nit: 1MiB in disk usage. it's 1MiB in size to begin with

> +du -sh $SCRATCH_MNT/test | _filter_scratch | _filter_spaces
> +
> +_scratch_unmount
> +_check_scratch_fs
> +
> +echo "Silence is golden"
> +status=0
> +exit
> diff --git a/tests/generic/466.out b/tests/generic/466.out
> new file mode 100644
> index 0000000..4c54d7a
> --- /dev/null
> +++ b/tests/generic/466.out
> @@ -0,0 +1,3 @@
> +QA output created by 466
> +1.0M SCRATCH_MNT/test
> +Silence is golden
> diff --git a/tests/generic/group b/tests/generic/group
> index fbe0a7f..65328c6 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -468,3 +468,4 @@
>  463 auto quick clone dangerous
>  464 auto rw
>  465 auto rw quick aio
> +466 auto quick dax
> --
> 2.9.5
>
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