Re: [PATCH v3] gfs2_grow: Optionally allow not issuing discard requests

[Andrew Price <anprice@redhat.com>]

On 19/02/2025 16:23, Mark Syms wrote:
> mkfs.gfs2 supports a -K option which disables issuing discard requests
> for unused blocks on the LUN. gfs2_grow does not have an equivalent
> option so even if the filesystem was originally created with the -K
> option a subsequent grow operation will incur the, potentially high,
> cost of performing the discard.
> 
> Signed-off-by: Mark Syms <mark.syms@cloud.com>
> 
> ---
> v2:
>   * Fix indentation of break statement
> v3:
>   * Update man page with the new option

Applied, thanks.

Andy

> ---
>   gfs2/man/gfs2_grow.8  |  6 ++++++
>   gfs2/mkfs/main_grow.c | 11 +++++++++--
>   2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/gfs2/man/gfs2_grow.8 b/gfs2/man/gfs2_grow.8
> index f1ba5e4e..ed962dca 100644
> --- a/gfs2/man/gfs2_grow.8
> +++ b/gfs2/man/gfs2_grow.8
> @@ -38,6 +38,12 @@ Prints out a short usage message and exits.
>   \fB-q\fP
>   Be quiet.  Don't print anything.
>   .TP
> +\fB-K\fP
> +Do not attempt to discard the block device contents. Issuing discards to the
> +device allows some solid state devices and sparse or thin-provisioned storage
> +devices to optimise free space. Other devices may emulate this behaviour by
> +zeroing the device contents, which can be a slow process.
> +.TP
>   \fB-T\fP
>   Test. Do all calculations, but do not write any data to the disk and do not
>   expand the filesystem. This is used to discover what the tool would have done
> diff --git a/gfs2/mkfs/main_grow.c b/gfs2/mkfs/main_grow.c
> index e378a668..2d74c3fa 100644
> --- a/gfs2/mkfs/main_grow.c
> +++ b/gfs2/mkfs/main_grow.c
> @@ -31,6 +31,7 @@
>   static uint64_t override_device_size = 0;
>   static int test = 0;
>   static uint64_t fssize = 0, fsgrowth;
> +static int skip_discard = 0;
>   int print_level = MSG_NOTICE;
>   
>   extern int create_new_inode(struct lgfs2_sbd *sdp);
> @@ -72,6 +73,7 @@ static void usage(void)
>   		"-T", NULL, _("Do everything except update file system"),
>   		"-V", NULL, _("Display version information"),
>   		"-v", NULL, _("Increase verbosity"),
> +		"-K", NULL, _("Don't try to discard unused blocks"),
>   		NULL, NULL, NULL /* Must be kept at the end */
>   	};
>   
> @@ -92,7 +94,7 @@ static void decode_arguments(int argc, char *argv[], struct lgfs2_sbd *sdp)
>   {
>   	int opt;
>   
> -	while ((opt = getopt(argc, argv, "VD:hqTv?")) != EOF) {
> +	while ((opt = getopt(argc, argv, "VD:hqTv?K")) != EOF) {
>   		switch (opt) {
>   		case 'D':	/* This option is for testing only */
>   			override_device_size = atoi(optarg);
> @@ -116,6 +118,9 @@ static void decode_arguments(int argc, char *argv[], struct lgfs2_sbd *sdp)
>   		case 'v':
>   			increase_verbosity();
>   			break;
> +		case 'K':
> +			skip_discard = 1;
> +			break;
>   		case ':':
>   		case '?':
>   			/* Unknown flag */
> @@ -207,7 +212,9 @@ static unsigned initialize_new_portion(struct lgfs2_sbd *sdp, lgfs2_rgrps_t rgs)
>   	unsigned rgcount = 0;
>   	uint64_t rgaddr = fssize;
>   
> -	discard_blocks(sdp->device_fd, rgaddr * sdp->sd_bsize, fsgrowth * sdp->sd_bsize);
> +	if (skip_discard == 0)
> +		discard_blocks(sdp->device_fd, rgaddr * sdp->sd_bsize, fsgrowth * sdp->sd_bsize);
> +
>   	/* Build the remaining resource groups */
>   	while (1) {
>   		int err = 0;