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From: David Sterba <dsterba@suse.cz>
To: Hans van Kranenburg <hans@knorrie.org>
Cc: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 06/15] btrfs: use raid_attr table in calc_stripe_length for nparity
Date: Fri, 17 May 2019 14:54:12 +0200	[thread overview]
Message-ID: <20190517125412.GA3138@twin.jikos.cz> (raw)
In-Reply-To: <318e980a-8b63-f425-804d-4d87a9d13d34@knorrie.org>

On Fri, May 17, 2019 at 12:06:05PM +0200, Hans van Kranenburg wrote:
> > -	default:
> > +	if (nparity)
> > +		data_stripes = num_stripes - nparity;
> > +	else
> >  		data_stripes = num_stripes / ncopies;
> > -		break;
> > -	}
> 
> A few lines earlier in that file we have this:
> 
>         /*
>          * this will have to be fixed for RAID1 and RAID10 over
>          * more drives
>          */
>         data_stripes = (num_stripes - nparity) / ncopies;
> 
> 1) I changed the calculation in b50836edf9 and did it in one statement,
> I see you use and extra if here. Which one do you prefer and why?

I did the cleanup only in the function and was not aware of the above,
but the ifs did not feel right so I'm glad you pointed that out.

And actually I think there must be an ultimate formula that also
includes the sub_stripes (raid10) and devs_increment (dup), this could
clean up the rest of the special cases.

> 2) Back then I wanted to get rid of that comment, because I don't
> understand it. "this will have to be fixed" does not tell me what should
> be fixed, so I left it there. Maybe now is the time? Do you know what
> this comment/warning means and if it can be removed? I mean, even with
> raid1c3 the calculation would be correct. There's no parity and three
> copies.

Yeah the comment does not help much, it was introduced by the monster
raid56 commit but I don't think there's anything to be fixed, regarding
raid1 or raid10.

  reply	other threads:[~2019-05-17 12:53 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-17  9:43 [PATCH 00/15] RAID/volumes code cleanups David Sterba
2019-05-17  9:43 ` [PATCH 01/15] btrfs: fix minimum number of chunk errors for DUP David Sterba
2019-05-17 14:05   ` Qu Wenruo
2019-05-17  9:43 ` [PATCH 02/15] btrfs: raid56: allow the exact minimum number of devices for balance convert David Sterba
2019-05-17  9:43 ` [PATCH 03/15] btrfs: remove mapping tree structures indirection David Sterba
2019-05-17  9:43 ` [PATCH 04/15] btrfs: use raid_attr table in get_profile_num_devs David Sterba
2019-05-17  9:43 ` [PATCH 05/15] btrfs: use raid_attr in btrfs_chunk_max_errors David Sterba
2019-05-17  9:43 ` [PATCH 06/15] btrfs: use raid_attr table in calc_stripe_length for nparity David Sterba
2019-05-17 10:06   ` Hans van Kranenburg
2019-05-17 12:54     ` David Sterba [this message]
2019-05-17 13:06       ` Hans van Kranenburg
2019-05-17  9:43 ` [PATCH 07/15] btrfs: use raid_attr to get allowed profiles for balance conversion David Sterba
2019-05-17  9:43 ` [PATCH 08/15] btrfs: use raid_attr table to find profiles for integrity lowering David Sterba
2019-05-17  9:43 ` [PATCH 09/15] btrfs: use raid_attr table for btrfs_bg_type_to_factor David Sterba
2019-05-17  9:43 ` [PATCH 10/15] btrfs: factor out helper for counting data stripes David Sterba
2019-05-17  9:43 ` [PATCH 11/15] btrfs: use u8 for raid_array members David Sterba
2019-05-17  9:43 ` [PATCH 12/15] btrfs: factor out devs_max setting in __btrfs_alloc_chunk David Sterba
2019-05-17  9:43 ` [PATCH 13/15] btrfs: refactor helper for bg flags to name conversion David Sterba
2019-05-17  9:43 ` [PATCH 14/15] btrfs: constify map parameter for nr_parity_stripes and nr_data_stripes David Sterba
2019-05-17  9:43 ` [PATCH 15/15] btrfs: read number of data stripes from map only once David Sterba

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