Re: [PATCH v4 1/4] btrfs-progs: mkfs: Enhance minimal device size calculation to fix mkfs failure on small file

[David Sterba <dsterba@suse.cz>]

On Tue, Nov 28, 2017 at 08:40:47AM +0800, Qu Wenruo wrote:
> 
> 
> On 2017年11月28日 07:21, David Sterba wrote:
> > On Wed, Nov 01, 2017 at 09:30:40AM +0800, Qu Wenruo wrote:
> >> +u64 btrfs_min_dev_size(u32 nodesize, int mixed, u64 meta_profile,
> >> +		       u64 data_profile)
> >> +{
> >> +	u64 reserved = 0;
> >> +	u64 meta_size;
> >> +	u64 data_size;
> >> +
> >> +	if (mixed)
> >> +		return 2 * (BTRFS_MKFS_SYSTEM_GROUP_SIZE +
> >> +			    btrfs_min_global_blk_rsv_size(nodesize));
> >> +
> >> +	/*
> >> +	 * minimal size calculation is complex due to several factors:
> >> +	 * 1) Temporary chunk resue
> >> +	 *    If specified chunk profile is SINGLE, we can resue
> >> +	 *    temporary chunks, no need to alloc new chunks.
> >> +	 *
> >> +	 * 2) Different minimal chunk size for different profile
> >> +	 *    For initial sys chunk, chunk size is fixed to 4M.
> >> +	 *    For single profile, minimal chunk size is 8M for all.
> >> +	 *    For other profiles, minimal chunk and stripe size
> >> +	 *    differs from 8M to 64M.
> >> +	 *
> >> +	 * To calculate it a little easier, here we assume we don't
> >> +	 * reuse any temporary chunk, and calculate the size all
> >> +	 * by ourselves.
> >> +	 *
> >> +	 * Temporary chunks sizes are always fixed:
> >> +	 * One initial sys chunk, one SINGLE meta, and one SINGLE data.
> >> +	 * The latter two are all 8M, accroding to @calc_size of
> >> +	 * btrfs_alloc_chunk().
> >> +	 */
> >> +	reserved += BTRFS_MKFS_SYSTEM_GROUP_SIZE + SZ_8M * 2;
> >> +
> >> +	/*
> >> +	 * For real chunks, we need to refer different sizes:
> >> +	 * For SINGLE, it's still fixed to 8M (@calc_size).
> >> +	 * For other profiles, refer to max(@min_stripe_size, @calc_size).
> >> +	 *
> >> +	 * And use the stripe size to calculate its physical used space.
> >> +	 */
> >> +	if (meta_profile & BTRFS_BLOCK_GROUP_PROFILE_MASK)
> >> +		meta_size = SZ_8M + SZ_32M;
> >> +	else
> >> +		meta_size = SZ_8M + SZ_8M;
> >> +	/* Only metadata put 2 stripes into one disk */
> > 
> > 'mkfs.btrfs -d dup' also works, so I think this should be handled here
> > the same way as metadata, right?
> 
> Just a few lines under.
> > 
> >> +	if (meta_profile & BTRFS_BLOCK_GROUP_DUP)
> >> +		meta_size *= 2;
> >> +	reserved += meta_size;
> >> +
> >> +	if (data_profile & BTRFS_BLOCK_GROUP_PROFILE_MASK)
> >> +		data_size = SZ_64M;
> >> +	else
> >> +		data_size = SZ_8M;
> >> +	if (data_profile & BTRFS_BLOCK_GROUP_DUP)
> >> +		data_size *= 2;
> Here data DUP is also handled.
> 
> So the problem is about the word "Only".

Yeah, it's confusing when comment does not match the code because it's
not clear what's the actual intention.

> Do I need to re-submit the whole patchset or just a separate patch to
> update the comment?

No, I'll update it myself as it is fairly trivial change.