Re: [PATCH 1/2] mkfs: default log size for small filesystems too large

[Eric Sandeen <sandeen@sandeen.net>]

On 2/27/14, 3:45 AM, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Recent changes to the log size scaling have resulted in using the
> default size multiplier for the log size even on small filesystems.
> Commit 88cd79b ("xfs: Add xfs_log_rlimit.c") changed the calculation
> of the maximum transaction size that the kernel would issues and
> that significantly increased the minimum size of the default log.
> As such the size of the log on small filesystems was typically
> larger than the prefious default, even though the previous default
> was still larger than the minimum needed.
> 
> Rework the default log size calculation such that it will use the
> original log size default if it is larger than the minimum log size
> required, and only use a larger log if the configuration of the
> filesystem requires it.
> 
> This is especially obvious in xfs/216, where the default log size is
> 10MB all the way up to 16GB filesystems. The current mkfs selects a
> log size of 50MB for the same size filesystems and this is
> unnecessarily large.
> 
> Return the scaling of the log size for small filesystems to
> something similar to what xfs/216 expects.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Looks good.

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

> ---
>  mkfs/xfs_mkfs.c | 48 ++++++++++++++++++++++++++++--------------------
>  1 file changed, 28 insertions(+), 20 deletions(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index d82128c..f7cf394 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -2366,32 +2366,40 @@ _("size %s specified for log subvolume is too large, maximum is %lld blocks\n"),
>  	} else if (!loginternal && !xi.logdev) {
>  		logblocks = 0;
>  	} else if (loginternal && !logsize) {
> -		/*
> -		 * With a 2GB max log size, default to maximum size
> -		 * at 4TB. This keeps the same ratio from the older
> -		 * max log size of 128M at 256GB fs size. IOWs,
> -		 * the ratio of fs size to log size is 2048:1.
> -		 */
> -		logblocks = (dblocks << blocklog) / 2048;
> -		logblocks = logblocks >> blocklog;
> -		logblocks = MAX(min_logblocks, logblocks);
>  
> -		/*
> -		 * If the default log size doesn't fit in the AG size, use the
> -		 * minimum log size instead. This ensures small filesystems
> -		 * don't use excessive amounts of space for the log.
> -		 */
> -		if (min_logblocks * XFS_DFL_LOG_FACTOR >= agsize) {
> +		if (dblocks < GIGABYTES(1, blocklog)) {
> +			/* tiny filesystems get minimum sized logs. */
>  			logblocks = min_logblocks;
> +		} else if (dblocks < GIGABYTES(16, blocklog)) {
> +
> +			/*
> +			 * For small filesystems, we want to use the
> +			 * XFS_MIN_LOG_BYTES for filesystems smaller than 16G if
> +			 * at all possible, ramping up to 128MB at 256GB.
> +			 */
> +			logblocks = MIN(XFS_MIN_LOG_BYTES >> blocklog,
> +					min_logblocks * XFS_DFL_LOG_FACTOR);
>  		} else {
> -			logblocks = MAX(logblocks,
> -				MAX(XFS_DFL_LOG_SIZE,
> -					min_logblocks * XFS_DFL_LOG_FACTOR));
> +			/*
> +			 * With a 2GB max log size, default to maximum size
> +			 * at 4TB. This keeps the same ratio from the older
> +			 * max log size of 128M at 256GB fs size. IOWs,
> +			 * the ratio of fs size to log size is 2048:1.
> +			 */
> +			logblocks = (dblocks << blocklog) / 2048;
> +			logblocks = logblocks >> blocklog;
> +			logblocks = MAX(min_logblocks, logblocks);
>  		}
> +
> +		/* make sure the log fits wholly within an AG */
> +		if (logblocks >= agsize)
> +			logblocks = min_logblocks;
> +
> +		/* and now clamp the size to the maximum supported size */
>  		logblocks = MIN(logblocks, XFS_MAX_LOG_BLOCKS);
> -		if ((logblocks << blocklog) > XFS_MAX_LOG_BYTES) {
> +		if ((logblocks << blocklog) > XFS_MAX_LOG_BYTES)
>  			logblocks = XFS_MAX_LOG_BYTES >> blocklog;
> -		}
> +
>  	}
>  	validate_log_size(logblocks, blocklog, min_logblocks);
>  
> 

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