[Ocfs2-tools-devel] [PATCH] discard unused blocks before mkfs

[Changwei Ge]

Hi Larry,
I have some quick questions:
1) It seems that your patch doesn't check if the backing disk is SSD or not, is 
that reasonable?
2) Why not just trim SSD before 'mkfs' performed by users? It's more 
straightforward.
3) Could you share some statistics telling the degree performance boosted.

Thanks,
Changwei

On 2018/2/24 12:15, Larry Chen wrote:
> From: Larry <lchen at suse.com>
> 
> When using a SSD as a block device, if unused SSD blocks could
> be discarded in advance, performance will be improved.
> 
> This patch uses ioctl interface to release unused blocks on SSD
> layer.
> 
> Signed-off-by: Larry Chen <lchen at suse.com>
> ---
>   mkfs.ocfs2/mkfs.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>   mkfs.ocfs2/mkfs.h |  9 +++++++++
>   2 files changed, 53 insertions(+)
> 
> diff --git a/mkfs.ocfs2/mkfs.c b/mkfs.ocfs2/mkfs.c
> index 354b2ee5..e9c8a9fb 100644
> --- a/mkfs.ocfs2/mkfs.c
> +++ b/mkfs.ocfs2/mkfs.c
> @@ -543,6 +543,48 @@ static void finish_normal_format(State *s)
>   	ocfs2_close(fs);
>   }
>   
> +static errcode_t _discard_blocks(State *s, uint64_t block,
> +		uint64_t count)
> +{
> +	int ret;
> +	uint64_t range[2];
> +
> +	range[0] = (uint64_t)(block) << s->blocksize_bits;
> +	range[1] = (uint64_t)(count) << s->blocksize_bits;
> +
> +	ret = ioctl(s->fd, BLKDISCARD, &range);
> +	if (ret < 0) {
> +		if (errno == EOPNOTSUPP && !s->quiet)
> +			printf("block discard not supported...skip\n");
> +		return errno;
> +	}
> +	return 0;
> +}
> +
> +static int discard_blocks(State *s)
> +{
> +	uint64_t blocks = s->volume_size_in_blocks;
> +	uint64_t count = DISCARD_STEP_MB;
> +	uint64_t cur = 0;
> +	int retval = 0;
> +
> +	count *= (1024 * 1024);
> +	count >>= s->blocksize_bits;
> +
> +	while (cur < blocks) {
> +		if (cur + count > blocks)
> +			count = blocks - cur;
> +
> +		retval = _discard_blocks(s, cur, count);
> +		if (retval)
> +			break;
> +		cur += count;
> +	}
> +
> +	return retval;
> +}
> +
> +
>   int
>   main(int argc, char **argv)
>   {
> @@ -615,6 +657,8 @@ main(int argc, char **argv)
>   		return 0;
>   	}
>   
> +	discard_blocks(s);
> +
>   	clear_both_ends(s);
>   
>   	init_record(s, &superblock_rec, SFI_OTHER, S_IFREG | 0644);
> diff --git a/mkfs.ocfs2/mkfs.h b/mkfs.ocfs2/mkfs.h
> index f9ba4dcf..ac9709f3 100644
> --- a/mkfs.ocfs2/mkfs.h
> +++ b/mkfs.ocfs2/mkfs.h
> @@ -41,6 +41,7 @@
>   #include <inttypes.h>
>   #include <ctype.h>
>   #include <assert.h>
> +#include <sys/ioctl.h>
>   
>   #include <uuid/uuid.h>
>   
> @@ -92,6 +93,14 @@
>   
>   #define MAX_EXTALLOC_RESERVE_PERCENT	5
>   
> +#define DISCARD_STEP_MB         2048
> +
> +#if defined(__linux__) && !defined(BLKDISCARD)
> +#define BLKDISCARD		_IO(0x12,119)
> +#endif
> +
> +
> +
>   enum {
>   	SFI_JOURNAL,
>   	SFI_CLUSTER,
>