linux-ext4 - Re: [PATCH V2] mke2fs: add discard to default mke2fs.conf and disable by default

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Message-Id: <6E0552E9-CEDA-4209-BFC3-D517D821D69B@redhat.com>
Date:	Thu, 18 Apr 2013 19:09:31 -0400 (EDT)
From:	Eric Sandeen <esandeen@...hat.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH V2] mke2fs: add discard to default mke2fs.conf and disable by default

On Apr 17, 2013, at 4:19 PM, Eric Sandeen <sandeen@...hat.com> wrote:

> Discard is a very big hammer.  If it succeeds, there's no undo
> or going back; on the other hand, on some devices the giant discard
> issued at mkfs time makes them go offline.  
> 
> Although I'm reluctant to waffle back and forth on default behavior,
> I think this disabling it by default the prudent thing to do.
> 

Ok, self-nak on this one, the folks in the hallway track convinced me that it was wrong.  I'll send another to handle it properly in mke2fs.conf, though.

Thanks,
Eric

> This patch also adds the discard option into the default mke2fs.conf
> file; although it could be set, it was not in the template.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> ---
> 
> V2: handle discard disable via "-K" since it's parsed *before* we get
> the default.  The extended options are parsed later, and will override
> the mke2fs.conf default without problems.
> 
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index 023ba49..a005eca 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -277,11 +277,11 @@ Attempt to discard blocks at mkfs time (discarding blocks initially is useful
> on solid state devices and sparse / thin-provisioned storage). When the device
> advertises that discard also zeroes data (any subsequent read after the discard
> and before write returns zero), then mark all not-yet-zeroed inode tables as
> -zeroed. This significantly speeds up filesystem initialization. This is set
> -as default.
> +zeroed. This significantly speeds up filesystem initialization. This is disabled
> +by default.
> .TP
> .BI nodiscard
> -Do not attempt to discard blocks at mkfs time.
> +Do not attempt to discard blocks at mkfs time.  This is the default.
> .TP
> .BI quotatype
> Specify which quota type ('usr' or 'grp') is to be initialized. This
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index bbf477a..fa11da6 100644
> --- a/misc/mke2fs.c
> +++ b/misc/mke2fs.c
> @@ -84,7 +84,7 @@ int    cflag;
> int    verbose;
> int    quiet;
> int    super_only;
> -int    discard = 1;    /* attempt to discard device before fs creation */
> +int    discard;    /* attempt to discard device before fs creation? */
> int    direct_io;
> int    force;
> int    noaction;
> @@ -1266,6 +1266,7 @@ static void PRS(int argc, char *argv[])
>    double        reserved_ratio = -1.0;
>    int        lsector_size = 0, psector_size = 0;
>    int        show_version_only = 0;
> +    int        nodiscard = 0;
>    unsigned long long num_inodes = 0; /* unsigned long long to catch too-large input */
>    errcode_t    retval;
>    char *        oldpath = getenv("PATH");
> @@ -1444,7 +1445,7 @@ profile_error:
>                      "should not be used anymore. Use "
>                      "\'-E nodiscard\' extended option "
>                      "instead!\n"));
> -            discard = 0;
> +            nodiscard = 1;
>            break;
>        case 'j':
>            if (!journal_size)
> @@ -1985,7 +1986,8 @@ profile_error:
>    lazy_itable_init = get_bool_from_profile(fs_types,
>                         "lazy_itable_init",
>                         lazy_itable_init);
> -    discard = get_bool_from_profile(fs_types, "discard" , discard);
> +    /* nodiscard is set if -K was used, extended discard opts parsed later */
> +    discard = nodiscard ? 0 : get_bool_from_profile(fs_types, "discard" , 0);
>    journal_flags |= get_bool_from_profile(fs_types,
>                           "lazy_journal_init", 0) ?
>                           EXT2_MKJOURNAL_LAZYINIT : 0;
> diff --git a/misc/mke2fs.conf.in b/misc/mke2fs.conf.in
> index 178733f..db6decb 100644
> --- a/misc/mke2fs.conf.in
> +++ b/misc/mke2fs.conf.in
> @@ -2,6 +2,7 @@
>    base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr
>    default_mntopts = acl,user_xattr
>    enable_periodic_fsck = 0
> +    discard = 0
>    blocksize = 4096
>    inode_size = 256
>    inode_ratio = 16384
> 
> --
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